eh DPSS EO e ia bsheaeae HS a Vike: a) = ch . fs aN. ae nats oe exh =~ Suh ctani waters 0b Cokatel 4 Set a — ANE eb AN Ald women ONAN TE ope g cat em oman ee see renton mee men ot set tee A AN Bale: Goyer mrt A ex tm ineranen mE BE SATS H -° Tooled So uw oa tenn oy ~ 50 60.09 0.8 O17 9-089 8 Te wees ae Sepp ea lean auSagegOa CUTS LE C205 SIE PARP Vt PCL TE EE es RARE ARS ONE GN AOA GUT At ORR RAT CARTE NATURAL HISTORY. SURVEY, ve initia rT Vy ‘ va Tel mF, ; . Mh any i 7 U et | ; ‘et a ; fe : i 1 Nfl By ee 7 a BULLETIN OF THE ILLINOIS STATE LABORATORY NATURAL HISTORY Urpans® [rirnois, U. S:A. VOLUME VIII 1908-1910 CONTRIBUTIONS TO THE NATURAL HISTORY SURVEY OF ILLINOIS MADE UNDER THE DIRECTION OF STEPHEN A. FORBES 1910 ILLtiInoIs PRINTING COMPANY DANVILLE, ILLINOIS CONTENTS. ARTICLE I. PLANKTON STUDIES. V. THE PLANKTON OF THE ILLINOIS RIVER, 1894-1899. PART II—CONSTITUENT ORGANISMS AND THEIR SEASONAL DISTRIBUTION. BY pace Cape OH ORDE a(S PIV AWNE) Se VER MOO Sy cai oe a see «cre 2-360 Li ETROLS ENCUTIO) Mies ss. ooo tenbagerp bgt es Meroe Ale Susi hei cnet es Sa DO at ee eee ae 1-17 Distribution of Collections-by Months)(@able) 72% 0.2... snes... a NUGUHOGS Here ee Aces tara Tn om haa are Cie migecu tote cascens # she eue Se mien Foe 5 P\coliefavonyel eye lennnvesaleses 4 cio cmie-a-citc! Oo.560 io cate tance OR ONO ce Cr en RI Sat ae 7 Wetimatiomsrm earch ee eit teins sve est ge ete ee as Oe RNa Piven ice ae 7 sie Conpositonion eae Planitonan wear arty ae eared ns hose 10 Comparison of Fresh-water and Marine Plankton.................. 12 OrcanismsrouumMenelamicbOnnanrt are ntis ae mate evecie a5 o aeavars aiteseel alga S 13 Constituent Groups of the Annual Plankton of the Illinois River(Table) 16 Discussion of the Statistical Data of the Species composing the Plankton OlacieslilinosMixiver tim) Le OAR 1 BO ON we trate ye niees Shanes 18-290 (CHAOS PREY AOE) 3 Seta carer crctto ches SAGA Become cos Re eo ere rua ire ry eer ers ae 18 —62 aAGUCTIACE Ce at eee Taree ioe Me ene, Me eee og Gada yaan huge te cotta cH 18 SI CIZO ONC CCS om ema nD eel ee pe ol sree eu tie, asl ueeoe UM toc eee mena etl 19 DiSCUSSTONPOIES PECIESS waar ert ho aes ene rea iis a cone ea 20 (Cloikarmoy ola (eSeag, Se! « 4p denne Sea eae eee OL we MERCER Ee Oks egrieek Chine Nn eae etree 22 DiSetSSION LOIS PECIES: Bree Het tue ee ee Ae eee RiGee rh eee 24 [Blea sill ea irertee (XSVESy s 5) ae Bees cake ecstetlenc cee Bo Rep Cale Se Ran ATS ee 34 Bactors controllmesDiatomebroduGhonen- 4s vere. saci: 35 —43 Diagram showing the seasonal distribution of diatoms, total plankton, nitrates, and thermograph and hydrograph of Illi- MOISURcnvietrabpblavaria tO GSO See ser are ere nares cies ain sie 37 ID ASHES oral“? SAGES ooo at Fane nile. oka ater oick a eka earl Gacmcan he retiree 43 (CG aly OMEN ZEN eI as ann oreo ely Crate Va) OREN OBR PSNR u ae Tee gars OR ed eee 59 IDSC RUS SToy ol OIE STOVXOWES., Aion ') dios Sun ul nld clupo mi bicle © Bin oleae S peal mone 60 [PA vais Olean ely ayekl g-cciidl ds idl ctc* coho. oicuty Oho Ble cecith ROKA cmc Tuer eC MeN eee Re IEE 62 IPARONOWOE), so lego cba mae a eit pkcud ChB Recs Suche netic eyo le keee CRCRCRE Me ar ont nen en ea raat 62 IAS EISIO PING aege cabertrer Meter eee ese er auiet Peele seinvcue Eiatsi sy Give isa: ose Be iastageane thal 63 Location and Amplitude of Pulses of Chlorophyll-bearing Organ- ismmcmnet Mem LMMIO1SeeiVeta Challe) ai aaa aee sc sis ae eis eres 64 IDISGUSSIONMO LS PECIES Ah rien 1h tetera ate teeta fcc h ib suet e Pepin 68 RUZ ODOC Ae ce pyar einen irapeyen ete cal Revaetics cick ots once eka Shei eoetaulae 92 DISCUSS ONMOlS DCCIESH Ey chim irere es Mean oise Sic) Sache 95 GOZO AR epee ER Be Se ee lee Nant gee encores co Sue Bear sie ante tes 113 IDISCHSSIGONTOMS PECleSt: ries -Reume hata ele fetes ais p cho sevettas one eee 113 S| OLORNOPAOE 2 A ulate Mente) et ofa eens Sucui we || Abie ep clas ie eats ia IC a cA 114 Ciliatameen eee Te he ney here eee oi ok td ce eaene owe 115 PAGE SOT Eh oho oe UR ee Ser i ere mans clair bic Dia Diego oo fs aleonl Discussion of Species: 2... 6. cee et cee ae oe ee ilsyil POTEET E e eeceo ected tiles cco geste lode nee sie Ale dads Mi cottMe ieee Ben aoe 132 @celenteratas.. ccc bu koh ele sad ne Mele ole ie See vere OF) ane icine ee 132 Platyhelminthes. 2.0.2.0. ee ee ete ea 133 ING RAS UIE RCS gine O eo ci One TCO eens temioto Pioimtarane tym o p,0 316" Ee cnc. 6 fio Ree atta kc oo eu Sek kn tk dene oibinie SARE heen otek GESHOG aay oe ns baie TAS AIG hog atte eo) cH aioe a it en 135 INGITETCIINLS # ee nk hich bid iste sed wealls the Rian dm Dyn el Dee he een 135 Niematielminthesac sai ccc cucu os cle my othe tuete mula SeeononCh oie hra tciene nee 135 IN Pray oY |: pe eee eae eemMenecem eG Diosbin ea seat! 0-0 0 oo 135 Acanthocephala... 3... 6. cee ee ee ee tee 136 PNG aGa HEU: an Re ete eee ee Oe eee AR oie Seetone ef dita cpto! Ooo. 0 oo 4 136 Oligoehzeta... oy. oe os = eee se Gree ae os ole) ela 136 IN(ayCohiGle oh 6 Aisin 6 ccolrevaus o On aiceAre Behe the Orene POE tise 1SyA FB OLOSOMMA TICS hs oy sah St cacao oe ret alleg seer iene RON neat een 137 [PAGY bier ne ae ap ae eh A De IRN eC ine r AMAL ROA SONOS nig’ ae so 138 RT ZO bas aes ocho eo cee haan ue ule cea Rene a ach 139 Discussion: of Species)... 4 «cite a wane vaca eee 140 Bdellowdaen2s 5 co ac Se ne oe ee Oe ee itn oe 141 WiscussionyOr Species: ..2 4 nO IRGISES OLED ZAGhiOnUs mttATiS Peele ee eee ee ee 179 Pt SeS OLB TAGIOMUS HOLLIS - eines Meio oe eee ne eee 181 Brachionus pala. Average number per collection............ 182 Rilsesotebvaciionus pala and vaniebics.m. 14 ene 184 Brachionus pala, type form. Sexual cycle.................. 188 Seasonal distribution of B. pala and its var. amphiceros....... 189 Seasonal wlimuitsiores. pala Wate dO7cdSanes eae eee 191 Rulsesiot Brachionusirecolaris:-...052)- sneer Brachionus urceolarts and varieties and B. variabilis. Average AUD eTEp el COLECHION art tat maiee ao e 0. eee eee 196 ulsesoteeOlLyantniauplaty Picra a en ne te eeee ee 204 POISESHOISW iG Clas Pecltinatan 2 0h oink) nie ee eee 211 RiulsesioteSyucheia: Sivlata. 2... Gee oe ee eee 213 PAGE IPISCSVOU PAT CTU Ce LOMOUSCLO mn = cers ayes] 21s. forest i cae rst ter 218 Seinbty OG a ee rear Mae TN ore Ae aa ents eg ears baat, pdt 219 Seasonal fluctuations of Pedalton mirum (Table)............... 220 ‘CoP TROY VENER eae incre ilies nce eRe ON Ep Ran eS eri trie <7 Cig” ate aa See a 22 IB SHRM ONAAO SIF (Cee alba a tes car ee Rens Gin ere ONss Raters Glenn PC ae ee ere yee een 22 ATG EO MOC Giana restarse: Ceara aie a ote aba einai okey iahias eter eeis sss epe 222 Paci Oee haere neta een wean «See cee are emt Sede emewes Teo te, y(t, 40 t 223 Cladocera and Hydrographic Fluctuations (Table).............223 Bsr Scion Om GDeGies eis tee eens etek ek te Biol irs eh DLO Tabular statistical data :— Bosmina and hydrographic fluctuations. 3228 Seasonal distribution of Chydorus. Average saan perm.*. .235 Effect of temperature on numbers of Chydorus...............238 A typical pulse of Daphnia cucullata. . SUhotmrarciauRae 4207 Diaphanosoma population, with data a temperature one river ENE lee 8s Sy 6) 8 Fire, okey Serer oes mtn Gc teem Reread cee a ee ee 248 Mormarandulnydrographie Changeset aise kigee eke et. ey: 254 COS RICO. FOSS oticna ere epee arornta 6 St dan, Bip oa acm alee eR onciaee eo ici Aeron ene”), eis OA OR SECIS ate. Hie re Mee en te ohne a sual orien Pt sein ch ins 258 CHOY SYEY OLOVG A corsa Bt eee phy eRe REINA CSO Eh cee eae ee pte a ee ar 258 Copepoda and: Hiydrocraphic Changes (Mable)i-s..-.22.--.-... 260 MISEUSSIONSOLS PC CIES arate ssiare suc tco nea ooceRie Seke eee Sey ete gle 261 Cyclops viridis and Hydrographic Changes (Table)............ 274,275 hum Per vob Ce yclopidc ((Cheple)s obows. he eke dah Maa eevee s 3% 278 J Ga] 01 Ny OOO ig aie, oomio yo Hu oka cata he ce Oe moe ete oe a aca ca te: ca eran 283 JNSeYEL TOMES LAT NS cesar eee Sloe: GPE Blane ohne eve MLN aS SEEN cea eee ne 283 GENET eos Bin Pe aM Re A eR cee ee ee Oa ar 283 BE A Clie el Cl Ae ge em nee Ne ee OTe garretts vie Be chin ise t tog oes te 284 | SIGSA OVO SIE“. BRAS cacae oh ork Regence od Ene HERR id 1a ge Ae ec NRC na eee eee ae 284 HS LET Ciel ieee eee ree tna Me Be RRO ee enh yi Me Ke 285 J al raaUTONASE Rag ey aah cht uo Chee tees OPENS ston! See Be eee Gr SOS Re ete Ev ee ne 285 [DNVOIGTATS Sra eee Bee Alec ctttece Maye, ch Oo fen 6 Secee aun ann Rann se a ee 285 iL USES Soa ae iar, Si PaiGt Jao arden ces Silene a 287 ESTED OXOVG ITA ate, clea Byrn ede RSI Bho aA. OLS Acie) ae eka peek cae 287 amare nes rcta Chal a aca apes oh er ce aac cen ca oN Seer eh tie Alek co 12, oy elageiid Me, a 287 [BAVA Ge F nnchele tee aeee aie, 3 ech enGeeh giinlee rh OF Bote RG OAR RCNP eae ee ee 288 IDISCUSSIONE OlnS DP CCLESE sgn eee ene ete ENE cole ok Stakaher dingy aL OS Periodicity in Multiplication of Organisms of Plankton............... 291-311 Comparison of Plankton Pulses and Lunar Cycle (Table)............296—299 GascousiGontents ofveond= Water (lable) - 442 4a9. 002 «esd 2 2 abel 306 Relation of Pulses of Chlorophyll-bearing Organisms to Lunar Cycle (lvoe) eremesr saree eee Oe Noe ee se ee aM ade 2. bos cs woe 308 General Considerations on, seasonal Changes... 227.000... 5.22... 2uh. 312 Pe ee MCE SE CMEC IY E DEE SEND ie facade och cies win Sees A e's ees ew, sae Oe Organisms per Cubic Meter in Illinois River in 1898 (Table)...........314-340 185i OY WV ayea RaW aN oak ok, Wahaus, AUG a Gre ae REPRESEN ae a Cr aeceee ech ey Ree eee sen 341-354 Dsl pina OUMOLe aes rm mie ee Hat eee ae eat eRe a eS AIS ee tale a Leite O vieralte oOOO vi PAGE Diagrams of Seasonal Distribution.......-..---+ +++ stent teers es 356-360 Wrrata and Addenda... 6... ee co ee le eee ie dis oe erty og eyes 361 ARTICLE II. NEW GENERA AND SPECIES OF ILLINOIS THY- SANOPTERA. BY J. DOUGLAS HOOD. AUGUST 22, 1908. (9 Text FIGURES)... (0.50. - 28 ee es es nae ea 361-379 INTRODUCTORY occ oes ce cisis oor cus el ehd Oe piles We pian rr 361 Descriptions of Genera and Species: Suborder Terebrantita. Family Thripide. Genus Heterothrips. . 1.0.6. 5 oo ee be pe es oo ie 361 [SING TTT Ee Se I OI COLO. G-8 2 aos 362 Genus Sericothrips. SH PUlChEllUs. <0 cose be Se es ee le ee ce 363 Suborder Tubilifera. Family Phleothripide. Genus Zygothrips. Zo, WONRICEPS «ac ve a os a ee ae ele oe Nghe 364 Gems LASSOLTEpS. 200. once Sees Oe se ee 365 TEL MAMSCOTINU Ac atonch eels Soscive. eM Oe Chetca gt Re ees ae 365 Genus Trichothrips. De AWLETIC ONS a Ae ate Ne aoe ORO Siete oreo nee 366 Di ANGUSTIGEDS ole cis oie) see aie toy 8 Ree er SOF De LOMPUUDUS (5 sre ils see ae a ke ge eee ceonaee eee pena 368 TE MOUINEC Ss wine cite tebe kel che te tarehalet tere GiGi Gontneen eat acs) ot tet a a 369 GRENMIS ULCCETOLITEDS 8 ucts ake ahs Ss ahelohe deus Cee 370 PN ANTENNGLUS Bi men Rey, Herne aL nA ENA eR ene ee ee 370 GeEMUS I VCOMEPS gio here ec bee onus raisin Bay cnet io der chee eee Swi INANGONLIGUSH ooo me eae 2 eto Le entra tonne dab Ae ee ee 372 Genas Aor pse nace se ee bis se oh owe ears ae AO 372 PI MCRACEPUGIUS. teleport. oc. Ub ae Soha helo eae tt eer SS) GenuseAcanthothrepsa (Key ton Species... 4.4)- 2 eee 374 PALO ZUTLALUS eek eres hots Dc aha sale avon sa Lake ore Cece ee ee 374 GENUS I AOTNTAD Sa Se eo cie 5 ols eicsusnoce ses Me stil eons) ohio slosh 375 ERMOGCUIAEUS RASS fer Mop Aa ccc Ginnie So ned tose Sag ee REC AC oe 375 Genus Cryptothrips. GRCARVONGIAWS oc machare fst slead eietece. ote SA oe eee 376 Genus [dolothrips. LE Chay NOS eR ero Or Are ieee aCRS neces Mire ete Pn ears 4:20 26 0 Sd Systematic Mist ion Species. 200 00... . <4 Su os Bon eke a 379 ARTICLE III. ON THE GENERAL AND INTERIOR DISTRIBU- TION OF ILLINOIS FISHES. BY STEPHEN A. FORBES: (LOZ MEABS) AS HA BRBRUAR Ys A909 es folk ete patos che a ones BO eae 381-437 EN DRODU CROR Veta mies cases ciel hed MenilA cnckt at elnda gay soe Colaba at eee 381 GeneralDistributioneae a 1otiotysos sted cca kas oe ee ee eee 383 Vil PAGE INTERIOR DISTRIBUTION. Table of Interior Distribution—by River Systems. Species and Num- HemomCollections 427 Generales uananmanyeercts tae cse sree atv nee eee oes ecoiet seach even eo 432 ILAKSIE OLE: WIENGES SI. Sa eoletee, Gane eee crete eas aceite ey eas ot erie SEA gr Remar ea AL erat 436 ARTICLE IV. THE ECOLOGY OF THE SKOKIE MARSH AREA, WITH SPECIAL REFERENCE TO THE MOLLUSCA. BY FRANK COLLINS BAKER. (20 Prates; 4 TExT FIGURES, INCLU- ID IN GaVEAE Per EB OUR vent Olle rasmus fae a omliueie, kt cg eee lew otek Ee ieweliane oy 441-499 HENS ODULC RUOIN ers Py ern ae eae pid ant wie Tete ce stp ena fave ree See cn Oys eye 441 WMerhrodmoiStidiyenetrs tea vert isie Picea inten Malas menrora craceuaerhi 441 N@ levy lISralteXeV aE TS Ye) ep Goo 5 a ha Seve o ore owe Mephoroe eee eas ASLO ets Pome wee 442 BconomerConsiderabionSs eye es cera sibs ieee hee ave bom tichet eae damone\eat 442 General sWoporrap lye waco eerie ee ere ene scuba tale) sy clisvavies sun = 443 Aemelener Si Ole) Mans nak mc crt, cys sa leud cutie ve ustoc a ae tatudin oeoce is Fabs 446 B. The Intermediate Ridge or Sand Spit.. ... 446 C. The East Branch of the North Branch oe ie Cea Teaver ee 447 1D); “Ware! CalerannpGroal Berle Rhee Gab a nogiinogadoddu os cube ae ae wa tic 447 DeEeiHeNorcheSraneh won tueiGhicaro Riven ict aes) oe ae 448 SCASOMAlM COMA TI SONG a pays Nee okies he, cok as ere Rene, Salil te Hye eocks 449 Detailed Discussion and Comparison of Stations:..2-.-...:.........- 449 Neem Komen Vatshe Startoncy leamcdnt ley memes 7. ae c a...) ai eta 449 Peep bnesliternneciate Ridge, stations PLE to XOX 3... FAS2 vill PAGE C. The East Branch of the Chicago River. Stations XXI to XXIX.472 D. Glenwood Beach Ridge. Stations XXX to XXXIV........... 479 E. North Branch of the Chicago River. Stations XXXV and De Sr A Eee Oke So oO MRR Ma aaa 484 Suma y seen ands ek radenela +, etal poem) oe ares et AE ae ar eo 484 Table of Terrestial Species. oc). 6. wi eb ee ee 487 Table of Phiviatile Species. cc a.52 ee ai, i i 488 MPARONOMAY sci nc tae cid eee ples Spiel ele die the 5.005 lm, aes oe ay eee sine 489 Systematic Catalogue of the Mollusca............:-:--2) 2: -meeee 491 Bibliography ee ee ee Se 95 fish (Forbes, 80) such as the Catostomide and some of the Silu- rid@ and minnows. I have found them in great abundance in the intestine of the adult gizzard-shad (Dorosoma), and in the contents of the digestive tract of the German carp (Cyprinus carpio). In the pages which follow, the seasonal distribution, or occur- rence in the plankton, of thirty-one Riuwzopoda is discussed, and the presence in the plankton of the Illinois of twenty-eight other rhizopodan forms which have been recognized by other writers as of specific rank is noted. This by no means exhausts the rhizopo- dan fauna of the environment which was the field of this investiga- tion. A continued study of the plankton itself would doubtless greatly extend the list of adventitious forms from ‘the shore and bottom, and a more careful analysis of the variants, especially in the Dijjlugia globulosa-lobostoma group, would still further increase the richness of the fauna from the systematic point of view. Hem- pel (99) lists sixteen species from this locality, and Penard (’02), in discussion, remarks: ‘Une pareille pauvreté dans une région riche en organismes de toute nature, est une impossibilitié maté- rielle.”’ However, neither Hempel’s paper nor the present one pretends to give a full account of all the Riizopoda of the region. He dealt largely with plankten collections, and the present paper deals with them exclusively. There is but little in plankton literature which gives with any fulness the seasonal distribution of the Riizopoda,or indicates that they are of any considerable importance in the economy of the plankton. The importance which they acquired in the plankton of the Illinois is no doubt in part due to the nature of the environ- “ment with which we are dealing. The somewhat sporadic and meteoric character of their appearances in our waters leads to the inference that full seasonal analyses of the plankton of other bodies of water at brief intervals may reveal a greater prevalence of the Riuzopoda in the plankton than has hitherto been detected. DISCUSSION OF SPECIES OF RHIZOPODA. Ameba limax Duj.—This was frequently abundant in the water- bloom of midsummer, but was not identified in the plankton collections. Ameba proteus Résel.—Average number, 342. The individuals here assigned to A. proteus include those taken in our plank- 96 ton which belong to the type of A. radiosa Ehrbg., a type which presents no distinctions sufficiently well-defined to separate it spe- cifically from the first-named form. It seems probable that A. radiosa includes small individuals of A. proteus which are not, at the time of observation, creeping upon a substratum; that is, they are limnetic, floating free with filamentous pseudopodia character- istic of that condition. Verworn (97) has shown that A. proteus takes the radiosa form in weakly alkaline solutions. Pond water rich in algze may have an alkaline reaction (Knauthe, ’98) in bright ~ sunlight. Larger individuals, distinctly referable to the A. proteus type when taken in the plankton, possess at times the slender pseu- — dopodia of the A. radiosa type as well as the blunter ones charac- teristic of the A. proteus form. I see no valid reason for separating ~ the two as distinct species. Most of the Ameba recorded from the plankton collections belong to the A. proteus type, the smaller ones — belonging to the radiosa type probably escaping through the meshes of the silk net. ; This species was found in 30 of the 180 collections examined, — being observed in all months of the year except May, November, — and December. The conditions attending its occurrence suggest that it is not, habitually at least, an active planktont at all seasons of its occurrence, but rather a tycholimnetic member, an invader from the littoral or bottom fauna, or a temporary accession during ~ the warmer months. In the first place, both the number of occur- ~ rences and the numbers of individuals found are small, and the seasonal distribution, plotted from the data of the collections of the five years, is exceedingly irregular. Furthermore, 17 of the 30% occurrences happened on rising floods, when the fauna of the bot- tom and shore of both the river and its tributaries is most mingled with the plankton. Further evidence of the agency of floods in introducing Ameba into the plankton is brought to light by a com-~ parison of its occurrences in 1897 and 1898. As shown by Plates — XI. and XII., Part I., the hydrograph of 1897 is much less irregular ~ than that of 1898, the latter year exhibiting repeated fluctuations in level due to floods. As a result we find Ameba occurring rela-~ tively (to the number of collections) almost twice as often in 1898 © as it did in 1897. It may also be significant that Ame@ba was not — found in November and December, months of unusual stability in ~ river levels. There is, however, a suggestion in the data of distri-~ Se 97 bution (see Table I.) that Amwba may become an active member of the plankton during the warmer seasons, like other Rhizopoda, as a result, perhaps, of the formation of gas or oil vacuoles in its proto- plasm. Of the 30 occurrences, 21 fall between April 19 and Octo- ber 17, with water temperatures of 58° and 56°, respectively. Of these 21 occurrences in warm waters but 8 accompany flood inva- sions, while all of the 9 occurrences during the colder months are in connection with such disturbances. Finally, the maximum num- ber per cubic meter (6,400) was found July 21 in clear waters, free from the debris of flood invasion. In conclusion, it seems probable that Ame@ba in warmer seasons of the year (above 56°) may adopt a limnetic habit. There is, however, the possibility’ that local and minor disturbances of the water due to current, waves, etc., are the occasion of its presence in the plankton in the absence of flood conditions. Jennings (’00a) reports both A. proteus and A. radiosa in the open water of Lake Erie. The range of temperature of river water in which Ameba was found was from 32° to 89°—the full extremes observed by us in the river at Havana. The temperature at the maximum occur- rence, July 21, 1897, was 82°. It is perhaps significant that 14 of the 30- occurrences of Ameba were between June 21 and Sep- tember 6, the period of maximum heat, the river averaging almost 80°—apparently the optimum temperature for the occur- rence of Ameba in the plankton in this locality. The relative numbers of individuals found in the various collections of the five years are too irregular to suggest any conclusions as to a seasonal cycle. Ameba verrucosa Ehrbg.—Average number, 19. This species was found but three times in the plankton, once each in May, August, and September, occurring but singly, and in each case in flood waters. It isapparently a tycholimnetic member of the plank- ton. The temperature limits of its recorded occurrence in the plankton were 58° and 82° respectively. Arcella. This genus is represented in the plankton by four species and two varieties which, like most of the Rhizopoda, are exceedingly variable, grading in some instances into each other by occasional ae 98 individuals which present intermediate characters. The majority of the individuals were taken in a living condition, though many empty shells were found. The conditions of the examination of the plankton and the opacity of many of the shells made it impossible to distinguish the dead shells in all cases. The records include many dead shells. Arcella costata Ehrbg.—Average number, 48. For the purposes of this paper I have included here all those individuals which possess an angular or ribbed shell. Leidy (’79) refers such forms to A. — vulgaris. Individuals of this type are rare, occurring infrequently and in small numbers. It was recorded but 18 times in the 180 collections, and the largest number per cubic meter was only 1,187. As in the other species of the genus, the warmer months are favored, fourteen occurrences falling in June-September 1n water at 70° or above. The other four records are one each in April, October, November, and December. The seasonal range of this form in the plankton thus falls in the main within the period of the maximum abundance of A. vulgarts, of which species it may be but a variant. Arcella discoides Ehrbg.—Average number, 972. This prevalent = species is not in all instances easily separated from A. vulgaris. Indeed, even Leidy (79) states that it graduates into A. vulgaris, and that he views it as the variety of this species in ‘“‘which the shell presents a greater proportionate reduction in height compared with the breadth.” In the enumeration of our plankton catches, the larger, flatter, and unornamented individuals have been referred to this species. Both the brownish and the hyaline forms should probably, for reasons hereafter given, be included here, and they are so grouped in the present discussion. Thus considered, A. discoides is the most abundant member of the river plankton be- longing to this genus, including two thirds of all the individuals observed. This species occurred in almost two thirds of the collections, hav-— ing been recorded in 115 of the 180, and more frequently and in larger numbers in the latter half of the five years than it was in the earlier period. This is in part explained by the unusual fluctua- tions of the river levels in 1898, during the maximum summer occurrence of the species. Like the other species of the genus, A. discoides has a period of maximum occurrence in the latter part of summer, as is shown in Table I. Of the 115 occurrences, 55 were in Of June—September, in water at or above 70°, while in the remaining eight months there were but 60 occurrences. This contrast is heightened by the ratio of occurrences to the total number of collec- tions, which in the period from June to September inclusive is 55 to 68 and in the remainder of the year only 60 to 112. The num- ber per cubic meter is also higher during this warm period, averag- ing for a single occurrence 1,376 to 1,028 for one in the remainder of the year. The average for the colder months falls to 850 if the large accessions attending the floods of February and November are omitted in the totals. The same causes efficient in determining the summer maximum in other Riizopoda of the plankton are doubtless operative here, and as in A. vulgaris the impetus of the summer in- crease is carried over into the autumn, causing a slight increase in numbers as compared with the numbers at corresponding temper- atures in the spring months. It seems probable that high temper- atures favor its occurrence in the plankton, not, however, directly, but because of greater abundance of food under those conditions, greater metabolism, and the storage of the products as oil or gas vacuoles which tend to lower the specific gravity and thus to bring the animal into the plankton. The adventitious occurrence of A. discoides in the plankton is shown by the fact that 45 of the 115 occurrences are with rising flood waters. The greater part of them lie in the colder months; in fact, nine tenths of the occurrences between October and May are correlated with flood movements. For reasons above given, how- ever, A. discoides may be regarded as temporarily adopting a lim- netic habit during warm months as a result of its physiological condition; at least many individuais of the species exhibit this habit during the warmer months. The data do not indicate that the open water is at any time the center of distribution of the species. There are no indications of recurrent pulses in the species and, as might be expected in case of adventitious planktonts, but little evidence of a characteristic seasonal distribution. There is some evidence that the summer is the period of most active multiplica- tion, and that an exceedingly transparent and hyaline form other- Wise resembling A. discoides is the young of this species. In 1898 separate records were kept of the two types with the result that they were about equally abundant—24,159 and 26,387 for the brown and hyaline types respectively. (8) 100 With but few exceptions the seasonal distribution exhibited by : the hyaline form was very similar in time and numbers to that of the Y brown form. Both occurred more frequently and in larger numbers in the warmer months, and irregularly and in small numbers in the colder waters. Both entered in larger numbers with flood waters. The differences though slight are suggestive. The hyaline form was © less frequent than the brown both in occurrences and numbers dur- — ing cold weather, and summer floods sometimes brought a rela-— tively larger number of the hyaline type. These are conditions} that might be expected if the latter is only the young (that is, the daughter organism occupying the new shell after fission of the oc-_ clusive, the data here presented seem to favor the view that they hyaline form is only a stage in the life history of the individual Arcella discotdes. The species A. artocrea Leidy and A. polypora Penard occur also : in our waters, but were included with A. discoides in the enumera- tion. Typical representatives of these species are not, however, present in any numbers Arcella mitrata Leidy was found but once—on Aug. 1, 1895, in. small numbers, at 78.5°. Arcella stellata Perty.—Under this designation are included only those individuals which have well-defined prolongations on the margin of the shell. Only a single occurrence in small numbers (48 per cubic meter) was recorded for the typical A. stellata — July © 29; 1895, at-a temperature of 75.5°. Arcella vulgaris Ehrbg.—Average number, 1,098. This species is somewhat more abundant than A. discoides, but occurred in fewer collections. It is a somewhat common planktont, whose seasonal distribution exhibits some irregularities attributable in part, as in cupant of the old) of Arcella discoides. In warmer months food is ~ more abundant and, presumably, fission more frequent. For this reason the young individuals abound at that time. Owing to the © difference in. the specific gravity of the two, the hyaline type is® more readily transported by flood waters. Though not con-§ —— a ————— ———o— rrr ES SS OEE Eee eee the case of other members of the genus, to flood conditions. It was | found in 61 of the 180 collections examined, and in approximately — one third of those made in each year, excepting in 1894, when it~ was not recorded, and in 1898, in which year it was found in about — 101 half the collections, the river levels for this latter year being subject to more than the usual disturbance. Arcella vulgaris is found throughout the whole year, with a marked predominance of occurrences during the warmer months, June to September inclusive, for during this period, in which a total of 68 collections were made, this species was found in the plankton 34 times. If the month of October be included, the ratio is 44 oc- currences in 83 collections, while in the remaining 97 collections, from November to June, only 17 occurrences were recorded. Of the 10 occurrences in October, 7 were in water at or above 55°. The season of frequency in the plankton thus ranges from June through October. In both frequency of occurrence and in numbers of individuals (see Table I.) there is an apparent maximum in August, preceded by an increase in June and July and followed by a decline in September and October. Arcella vulgaris thus seems to be a late summer planktont. The continuance into October may in part be due to the temperature conditions above cited, and perhaps also to constant seining of the river bv fishermen in the low-water stages at that time, causing repeated disturbances of the bottom and shores, where Arcella habitually lives. This maximum frequency of Arcella during the warmer months in the plankton is, however, probably due to the formation of gas or oil vacuoles in the plasma under the conditions of higher temperatures. Their flotation is thus facilitated, and they become, in a way, semi-active but temporary planktonts. That floods are also in part responsible for the presence of Arcella in the plankton is evident from the fact that 32 of the 61 occurrences come with rapidly rising waters, or shortly after rapid rises, during the interval of rapid decline. The larger numbers of individuals also appear in flood-waters, occurrences of more than 1000 per cubic meter happening 10 times with floods to only 4 in more stable conditions. The maximum occurrence, 25,272 per cubic meter, came with the flood of February, 1898, indicating the presence of this species in large numbers, even under winter conditions, in some local environment tributary to the flood plankton. The average number per cubic meter in the 61 collections con- taining Arcella was 1,260; and the maximum, 25,272,as above noted. This species occurred in only 10 collections in stable conditions of the river, when the temperature of the water was below 55°. The 102 average number of individuals in these cases was, however, only 230 per cubic meter as against 1,443 when the temperature was above 55°, or, if below, when floods prevailed. The seasonal and numerical distribution of occurrences and individuals alike point to the agency of floods and higher temperatures in the introduction of Arcella into the plankton from its usual habitat, the bottom and the shore. This species occurred in water ranging in temperature from 32° to 89°. Being a bottom form, the plankton data do not afford a satisfactory basis for determining its true seasonal distribution and optimum temperature. The maximum number found, 25,272, was in water at 32°; but this was an isolated occurrence in a flood, and serves only to illustrate the irregularity of distribution in the plankton of tycholimnetic organisms. Centropyxts aculeata Stein.—Average number, 570. This species has appeared in collections in every month of the year, but its sequence is frequently interrupted and its numbers are quite irregu- lar. Practically without exception all the larger occurrences attend rising flood waters. It is evidently adventitious at all seasons of the year. Centropyxts aculeata var. ecormis (Ehrbg.) Leidy.—Average number, 604. In former years this species was less frequent than the preceding species. Its appearances in the plankton tend to coincide with those of C. aculeata (Table I.), and are doubtless due to the same causes. Thus in the February flood of 1898 there is a pulse of 12,636 of C. aculeata and one of 9,477 of var. ecorms. C. levigata Penard seems to be identical with this variety. The data concerning both C. aculeata and its variety ecormis are too irregular to throw any light on the seasonal cycle of these adventi- tious planktonts. Cochliopodium bilimbosum (Auerbach) Leidy.—Average number, 1,384. This species was found in the plankton during 1898 in irregular numbers in 27 of the 52 collections. The distribution of the occurrences afforls indubitable proof of their close dependence upon flood waters. In 15 of the 27 cases Cochliopodium appeared with a rising river, and in all but 6 cases, in periods of considerable movement in river levels (cf. Table I. with Pl. XII., Pt. I.), such as the rising flood of January and February and the repeated minor eee Se eee eee ee ee ee, ae Se ee ee a ee Oe a a Oe ee 103 fluctuations of August and the following months. The year 1898 was one of unusual irregularity in the hydrograph (Pt. I., Pl. XII.), especially at the lower stages of the river, at which times this rhizopod appeared most frequently. Its maximum occurrence, 20,898 per cubic meter on Jan. 25, accompanied a rise of 0.6 of a foot in 24 hours. At other times the numbers range from 100 to 8,000 per cubic meter, their irregularity affording additional ground for regarding this species as an adventitious planktont. Cochliopodium was present in water ranging from 32.1° to 89°, the maximum number observed being found in water almost at the freezing point, when the river was full of running ice. That this is the optimum temperature for this organism is not, however, to be inferred, since, as has been shown above, this species is adventi- tious in the plankton. Plankton collections do not afford adequate data for determining the seasonal cycle of the organisms habitually living upon the bottom. This species was not found, though careful search was made for it, in the winter collections of 1899. Its absence from the records of years previous to 1898 may in part be due to a failure to observe it in the silt-polluted collections in which it is most apt to occur. Cyphoderia margaritacea Ehrbg.—Average number, 198. This Species has occurred in every month but February. In 1898, the majority of the occurrences and three fourths of the numbers ap- peared between May 1 and October 1 at temperatures above 60°. It was never abundant at any time, though there is this indication of its increased numbers during the warmer season. It is not an im- portant element in our plankton. Apstein (’96) found it somewhat irregularly in the plankton of German lakes. In our waters it exhibits no marked dependency upon floods for its presence in the plankton, though it is probably capable of assuming the limnetic habit in the warmer season. Cyphoderia trochus Penard appeared occasionally with the pre- ceding form, from which it is distinguished by its conical horn on the fundus and by its larger scales. Difflugia. This genus is the most abundant one of the Riizopoda in the meokton of the Illinois River, and is a factor of quantitative 104 importance initseconomy. It includes a number of forms notorious for their variability and for the difficulty with which specific dis- tinctions can be applied. I shall discuss the species as they were enumerated, and shall correlate my work with Penard’s (’02) recent elaborate analysis of the species so far as I can with the aid of my notes in the absence of the collections. Opinion as to the validity of the species is expressly withheld excepting in those instances in which it is formally stated. Diffiugia acuminata Ehrbg.—Average number, 315. This spe- cies has occurred in every month of the year and in 83 out of 180 collections. In 1898, two thirds of the occurrences and three fourths of the individuals were taken between May 1 and October 30, at temperatures above 70°. In this year there are six recurrent pulses from June to November, but all but one of these are found on rapidly rising flood waters, and they bear no constant relation to the pulses © of diatoms previously noted, with which in some instances they — are intercalated, though this is not regular or constant. Similar ~ tendencies to appear with floods and in greater numbers and more frequently in summer can be detected in records of other years. It” was more than twice as nee in 1896—a year of interrupted hydrograph (Pt. I., Pl. X.)—as in 1898. This is one of the larger) and heavier rhizopods, i its occurrence in the plankton is doubt-— less adventitious, due to floods and currents, and its greater numbers ~ and frequency in the summer may result from its greater abundance ~ at that season in its natural habitat, the shore and bottom, and ~ perhaps, also, from its lighter specific gravity during the warmer season. An illustration of this appears on the rising flood of June, 1897, when the maximum number recorded (10,000 per m.*) oe- curred. E. The shell of this species is exceedingly variable in size, constitu-_ ent particles, and proportions. A number of forms separated by Penard (02) and others as distinct species were grouped under D. acuminata in the enumeration. The greater number of these belong to the type designated by this name by Penard (’02). D. acuminata var. inflata Penard and the somewhat similar D.elegans Penard are not uncommon. JD. acuminata var. umbilicata Penard, D. elegans ' var. teres Penard, D. curvicaulis Penard, D. lanceolata Penard, and D. scalpellum Penard occur also, but are rare. lll oa eee 105 Difflugia bicuspidata Rhumbler.—Average number, 76. A sep- arate record was kept of this bicuspid type in the later years of our collections. Penard (’02) regards it as a synonym of his D. elegans, though it would seem to be as worthy of specific distinction as many other variants to which he accords this rank. It varies greatly in the relative development of the accessory “horn,”’ which is sometimes but a mere elevation near the base of the main horn. Individuals with equal and symmetrical horns represent the other extreme. Ina few cases tricuspid individuals have been seen, evidencing a tendency to vary towards the type found in D. varians Penard and D. fragosa Hempel. This form was about one fourth as abundant as D. acuminata, and eight of the ten occurrences fall between May and October, usu- ally with D. acuminata and presumably for the same reasons. Difflugia constricta Ehrbg.—Average number, 46. This species occurs irregularly at all seasons of the year without marked prefer- ence for the warmer months, and often, but not always, with flood waters. It occurs throughout the whole range of temperatures, and the largest number (2,778 per m.*) appeared during the decline of the spring flood. Data are too infrequent to establish any seasonal routine. This species varies greatly, and is connected by an unbroken series of variants with the genus Centropyxis. Penard (’02) also notes the existence of this connection, and states that after careful search he was unable to find any constant distinction which would suffice for its separation. In my enumeration only the elongated and smooth individuals were referred to this species. The spinose forms were referred to Centropyxis aculeata, and those similar in form to the spinose type; but those free from spines, to C. aculeata var. ecornts. Diffiugia corona Wallich.—Average number, 36. -In 1896, when the hydrograph was much disturbed, the average number was more than twice as great. This superb species was found in every month of the year except December, but never in large numbers. Its large size (200-300 »), and its heavy shell militate against its pres- ence in the plankton, and its occurrences are irregular and its num- bers few. There is no marked preference for warmer months, and four fifths of its occurrences are in rising flood waters. It is plainly 106 an adventitious planktont. The data are too irregular to trace its seasonal distribution. As a species it is as well defined as any in the genus. It is not in our waters connected by intermediate forms with other species. Its assignment to D. lobostoma by Schewiakoff (’93) 1s not in my opinion justifiable unless we regard all forms of Dzffiugia as belonging to one species. Difflugia fragosa Hempel.—Average number, 25; in 1896 over 100. This species occurred in every month of the year but Febru- ary, though three fifths of the records and the majority of the in- dividuals were found between May and October at temperatures above 60°. The data are too irregular to trace the seasonal history of the organism, but they suffice to suggest the agency of floods at all times and of high temperatures during the summer, as factors in the occurrence of the species in the plankton. The shell of this form is relatively to that of other species rather heavy, and this fact combined with the irregularity of its occurrence seems to justify the conclusion that it is largely adventitious at all seasons of the Wear The species exhibits a great deal of variation in the development of the central spine—Hempel (’99, Fig. 1)—and in the number and arrangement of spines in the accessory circlet. The mammillate form of the central spine figured by Hempel is not usually present. Individuals in which the central spine is but feebly developed seem to connect this species with D. varians, recently described by Penard (’02). Otherwise, and in our waters, the species is well delimited. Difflugia globulosa Duj.—Average number, 7,194; in 1897, 47,329, the larger number in this year being in part due to a remark- able pulse of 1,240,000 early in September. This is the most abundant of all the rhizopods in our plankton, occurring most frequently and in largest numbers. It is found in every month of the year, and in1898 appeared in every collection except four in De- cember. With a few exceptions in the autumn of 1898 (Table L.), no large development (exceeding 10,000 per m.%) has taken place earlier than May or later than September—that is, at temperatures below 60°. The occurrences are most continuous and the numbers of individuals are largest during the warmer period between the months named. ‘The largest pulse, that of 1,240,000 on September 107 7, 1897, was at 80°. A pulse of 48,000 on November 22 at 40° gives evidence of considerable range in adaptation to temperatures. In Table I. the seasonal distribution of D. globulosa is given in full. It differs from that of previous years mainly in the fact that the summer pulses do not here have the amplitude reached in other years; for example, in 1896 (252,000) and 1897 (1,240,000). It is characterized by considerable irregularity caused by somewhat abrupt pulses at irregular intervals. A comparison of these occur- rences with the hydrographic conditions (Pt. I., Pl. XII.) indicates that in the colder months increase in numbers in the plankton at- tends flood waters only, as, for example, in January, February, late October, and November. In the summer, pulses may also come with floods. For example, that of 252,000 on May 25, 1896, ap- peared on the upward slope of the June rise of the year, and that of 80,000 on June 28, 1897, came with the belated June rise of that year. On the other hand, some of the minor fluctuations appear on declining floods, and the maximum one of our records, that of Sept. 7, 1897, came in the midst of the most prolonged period of mame low water (Pt. I., Pl: XI.) found in the six years of our operations. From these facts it is evident that floods are efficient in increasing the number of D. globulosa in the plankton, and that the amplitude of the pulses to which they contribute is much greater in the warmer months (above 60°) than in the colder ones—as a result, perhaps, of the greater numbers present in their normal habitat, the shores and bottom, and also as a result of their readier flotation at this season. In so far as their presence is due to floods they are adventitious. On the other hand, it is very probable that they become temporarily eulimnetic in habit during the summer months. The evidence for this lies in their greater numbers in a period which is predominantly one of greater stability. Thus in 1898, in the 22 collections between May 1 and October 1, the average number present is 9,731, while in the remaining seven months of colder weather the number is only 5,200. Additional evidence arises from the fact that pulses of unusual magnitude have occurred quite independently of any factor such as flood or other disturbance which might cause their adventitious introduction into the plankton. Thus on Sept. 7, 1897, there is a symmetrical pulse whose rise and decline occupy four weeks, as shown in the following table. The total change in river levels in this period of four weeks (Pt. I., Pl. 108 Date Number perma | Gurbidity, | Silt siver above HN GMCS Ibm ego 8,0 oa oc | 4,800 SOM, .15 1.8 INCNTESG Silla A chan mae weet | 112,000 5 Oe) .19 1.8 Seaieuieee Tk Abaca ust | 1,240,000 15 AS 1.8 SeouemMoge We ns ca on soe | 106 ,000 2 Os) 1.04 2.0 syejoueesanloyeye Wily aw gcinn ooo ¢ 800 | F555) | trace 2.0 XI.) was only a fall of .1 and a rise of .2 of a foot—changes due to wind and the operation of the locks in the dams at either end of the pool. The estimated percentage of silt is near the minimum—from a trace to 5 per cent.—and the turbidity was no greater than is customary (Pt. I., Table III.) in our waters during periods of abun- dant plankton such as this (Pt. I., Pl. XI.). Beyond the presence of these rhizopods there was nothing in the plankton to suggest that the bottom had been stirred up any more than usual. No environmental factor is apparent to which we can attribute this wave of Dzfflugia in the plankton. It is due, I believe, to their own physiological condition. This was a time of prolonged low water and great sewage contamination, and of remarkable development of water-bloom, chlorophyll-bearing flagellates, unicellular alge, and some diatoms,—all elements in the food of Dzfflugza. In the open water Difflugza could find abundant sustenance and thus maintain itself there. It is not strange, then, that we find it in these warm waters, richly charged with its food, assuming for the time a eulim- — netic habit, perhaps as a result of rapid growth and lighter shells, and ~ of increased metabolism—with reserve products which lighten the specific gravity and so facilitate flotation. This species is found throughout the whole range of temperatures. There are indications that its optimum lies above 60°, and perhaps — near the maximum, 80°. This may, however, be the result of the effect of temperature upon the food supply of the organism. Inany ~ case the plankton data can not suffice to follow the complete seasonal cycle of an organism which is either an adventitious or but a tem- porary constituent. 109 The question of specific limits and variation in this organism is one of exceeding difficulty, and I see no satisfactory solution for it until some one attacks the problem by a study of the variation by modern quantitative methods, and endeavors by breeding under control to establish the limits of variation within the normal range of seasonal changes of the environment. When this is done, some. more satisfactory criterion for species in this group of planktonts will be feasible than the present condition affords, in which slight differences from previous descriptions are held to be valid for specific distinctions. Thus, in recent years, species of plankton Difflugia have been described by Heuscher (85) (D. urceolata var. helvetica) from Swiss lakes; by Zacharias (97) (D. hydrostatica) from Lake Plén; by Garbini (98) (D. cyclotellina) from Italian lakes; by Levander (’00) (D. lobostoma var. limnetica) from Finnish waters; and by Min- kiewitsch (’98) (D. planktonica) from Russian waters. All of these forms occur in the Illinois River, and there are others equally worthy of specific designation in our plankton as yet undescribed. They occur most abundantly at the times of the pulses, especially of those in stable conditions. In my opinion they are all mere limnetic varieties of D. globulosa or D. lobostoma, the form of the shell and its constituent particles being modified by the habit of life in which these individuals of the seasonal cycle are found. They occur at times of abundant food, rapid multiplication, and limnetic environ- ment. Their shells are accordingly lighter, more chitinous and transparent, and the foreign particles adherent to them partake of the nature of those of the silt in suspension. This, however, is merely an opinion based upon an examination of the statistics of occurrences, and upon the work of plankton enumeration in which all individuals must be assigned tu some species. This is at least a different point of view from that of the systematist, who may, per- haps, lay more stress upon divergences from described types and less upon links connecting such variants. For the sake of genuine progress in the science it would seem to the writer extremely desir- able that more attention be given to the question of variation and less to the description of new species under criteria now in vogue. It may be desirable, indeed necessary, to distinguish such forms in the plankton. It would be both safe and conservative to designate them as forms, or, at the most, as varieties. 110 The location‘of the pulses of D. globulosa bears no constant rela- tion to those of other organisms, owing, in part, at least, to the irregularities of the floods upon which some of them seem to depend. - The great pulse of Sept. 7, 1897, is intercalated between two pulses of diatoms and other. chlorophyll-bearing organisms, and some others bear a similar relation to their food supply, while some co- incide with an increase in these synthetic organisms (cf. Table I. andaeh in)s ; Difflugia globulosa and the following species were reported by Smith (’94) in the plankton of Lake St. Clair; by Jennings (’00a) in that of Lake Erie; and were common in the plankton of Lake Michigan (Kofoid 95). Difflugia of the forms included here under D. globulosa and D. lobostoma have been reported by many authors from various European lakes and rivers, but in no reported instance do they reach the numbers or importance in the plankton that they do in the Illinois. Full records of their seasonal distribution may, however, bring such importance to light. Difflugia lobostoma Leidy.—Average number, 1,158. In the total of all collections it is about one fifth as abundant as D. globu- losa. Like that species it occurs throughout the whole year in almost every collection (Table I.), and the fluctuations in its occur- rence follow very closely those just described for D. globulosa in the direction of their movement. The amplitude of the pulses is less, as a rule, and their culminations and limits are coincident, or at least approximate. Thus, on Sept. 7, 1897, D. lobostoma attains only 24,000, and the pulse of D. globulosa on June 28 (80,000) is attended by one of 96,000 in D. lobostoma in the next collection, on July 14. There are in this species also the same influx into the plankton with floods, and increase in numbers at temperatures above 60°. There are 954 per collection per cubic meter below this temperature to 1,436 during the warmer months in 1898. There are also pulses during the warmer months, in stable conditions, coincident with those of D. globulosa. Similar causes presumably contribute to these results in both species. Difflugia lobostoma is also exceedingly variable in proportions, in the texture of the shell and the degree of incision, and in the num- ber of lobes about the mouth. Two, three, and even four have been noted, and they vary greatly in depth, in regularity, in perfection of their development, and in the structural border which sometimes fall forms their margin. Chitinous, brownish, or more or less trans- parent shells are abundant when pulses occur. Forms which connect this species with D. globulosa have been observed. In-’ cluded with ). lobostoma are forms which have since been described by Penard (02) as D. gramen, D. gramen var. achlora, and D. lithoplites, though I have not found in the Illinois plankton any of the last-named with the peculiar tipped horns found by Penard upon many individuals of his species. Difflugia pristis Penard (?).—A small Difflugia was found occa- sionally in the filter-paper collections in the colder months,. but only from November to March. It was often dark, or even blackish, resembling in this respect Penard’s D. pristis. Individuals not thus darkened approach more nearly D. fallax Penard and D. pulex Penard. Difflugia pyriformis Perty.—Average number, 368. This species occurred in every month except January, but generally in small numbers and irregularly. The largest number taken—12,000, on May 25, 1896—came with the flood at that time (Pt. I., Pl. X.), and all the large occurrences of 1898 came with rapidly rising water (cf. Table I. and Pt. I., Pl. XII.). There are no indications of pulses during stable conditions, and we must conclude that the species is purely adventitious in our plankton. It is one of the largest species with a heavy shell, and its flotation is impeded thereby. This species is exceedingly variable. The following varieties or variants, given specific rank by some writers, have been noted, and are included with D. pyriformis in the enumeration: D. pyriformts var. nodosa Leidy, D. pyriformts var. claviformts Penard, D. pyriformis var. venusta Penard, and D. pyriformis var. lacustris Penard. A more slender and smoothly contoured form than the last is not uncommon. D. capreolata Penard and D. bacillifera Penard were also found, but are rare. Diffiugia rubescens Penard was taken but once—on May 25, 1896. Difflugia tuberculosa Hempel was also found but once in the planktons enumerated, though Hempel (’99) reports it as appearing occasionally from August to November in 1895. D1ffiugia urceolata Carter was taken only in April and May, 1896, in small numbers at temperatures of 66°-80°. {12 Dinameba mirabilis Leidy was found in the plankton but once—Apr. 12, 1898, in small numbers, at 52°. Euglypha alveolata Duj. was found in small numbers in the plankton, but only on Nov. 1, 1898, and March 14, 1899, at tempera- tures of 45° and 36°. Euglypha ciliata Ehrbg. appeared in the filter-paper collections in 1897, in July, August, and November, in small numbers at tem- peratures ranging from 80° to 48°. This is said by Penard (’02) to be predominantly a sphagnum species, but’ widely distributed elsewhere in small numbers. Euglypha levis Perty.—This minute rhizopod was found in the filter-paper collection of Oct. 4, 1898, at 72°. Nebela collaris Leidy was found only once—on June 25, 1898, at SO. a Pontigulasia incisa Rhumbler.—This curious rhizopod occurred in the plankton in July and August, 1895, and again in August and September, 1897, at temperatures of 75°- 85°. Both occurrences were in stable conditions, and the temporary adoption of the lim- netic habit is suggested by their appearance at these times. Two other records in 1897—on March 22 and November 9, at 44° and 50°— extend the seasonal range of the species. These occurrences attended rising water and were apparently adventitious. Trinema enchelys (Ehrbg.) Leidy.—Average number, 158. This little cosmopolite rhizopod of the sphagnum fauna was found but eight times in the plankton. The individuals observed were all dark-_ ened by the granular food vacuoles to such a degree that structural details were obscured. It was noted only in the somewhat turbu-— lent years of 1898 and 1899, though on account of its small size and the obscurity of its structure it may have been overlooked in previ- © ous collections. The few occurrences are insufficient to establish any seasonal routine. They were at both extremes of the tempera- ture range and in all seasons but spring, with a predominance in late” summer and fall. The species is evidently adventitious in the plankton, as shown by irregular distribution and small numbers, and by the fact that its occurrences coincide in all instances but one with rising water. - a ta Besar cores rts HELIOZOA. The Heliozoa of the plankton of the Illinois are few both in number of species and of individuals. They apparently play but a small part in the economy of the plankton. The average number for 1898 was but 4,883. Their occurrences are confined in the main to midsummer and early autumn. But four species were identified, though several others remain undetermined for lack of sufficient material, especially of the living forms. Apstein (’96) reports Helitozoa in considerable numbers in German lakes; with maxima in July-August. It is probable that these delicate forms are fre- quently crushed in manipulation or hidden in silt in our collections. DISCUSSION OF SPECIES OF HELIOZOA. Actinophrys sol Ehrbg.—Average number, 62. This species occurred irregularly from April to the early part of November at temperatures above 46°. It was recorded most frequently in the latter part of the summer, the largest number (28,000) appearing Sept. 7, 1897, at 80°. Actinospherium etchhornu (Ehrbg.) Stein.—Recordeda few times, from July to October, at maximum temperatures (75°-80°), but always in small numbers. Endophrys rotatoriorum Przesm.—This heliozoan (?) has been recently described by Przesmycki (’01) as parasitic, during a part of its existence, in Philodina and Hydatina. A parasite resembling this parasitic stage of Endophrys was observed by me in a bdelloid rotifer (Kotijer tardus) on several occasions, but it was never abun- dant, nor was its connection with any free-swiniming condition noted. The heliozoan affinities of this organism seem very ques- tionable. Nuclearia delicatula Cienk.—Average number, 4,760. This species in 1898 appeared first on June 21, attained a pulse of 78,400 on August 9 at 82° and another abrupt one of 65,600 on September 27 at 73°, and made its last appearance October 25 at 48°. Occur- rences in previous years are confined to midsummer. Its optimum conditions of temperature obviously lie near the summer maximum, and its lower limits near 50°. Its appearance in the plankton is not traceable to flood conditions, and it is apparently eulimnetic in our waters. 114 Hempel (99) reports Raphidiophrys pallida Ehrbg.and R. elegans Hertwig and Less. in the plankton of Quiver Lake adjoining the river, and I have found an undetermined species of Acanthocystis and a small heliozoan resembling Nuclearia in the river plankton. SPOROZOA. Triactinomyxon sp.—In the plankton collections of each year there have been found free limnetic spores which unquestionably belong to that highly aberrant and peculiar group of organisms described by Stolé (’99) as Actinomyxidia and regarded by him as Mesozoa, but later referred by Mrazek (’00) Caullery and Mesnil- (04), and Leger (’04) to the-Myxosporidia. The organisms de- scribed by Stolé were parasitic in fresh-water oligochetes, and it is not improbable that the limnetic spores taken in our plankton collections are derived from parasites in some of the numerous aquatic oligocheetes, or other invertebrates, found along the bottom and shores of the stream. The species here referred to Triactinomyxon differs in some details from T. 1gnotum Stolé. It was found in the course of the six years at least once in every month of the year, but most regularly © in May—September, and rarely and in small numbers in the colder months. Its transparency and long, slender, radiating, tripod-like arms give it a typically limnetic habit. Aenean. yxidia, gen. et sp. indet.—Clusters of eight, or less) cylindrical spores radiating from a common center and bearing a marked resemblance in structural features to those of Triactinomyx- on, but lacking any anchor-like projections, were found sparingly in the plankton in June—September. The distinctively limnetic habit of these spore stages in the life- history of these parasites is unique among the See and has not, to my knowledge, been before noted. | Many of the rotifers of the summer plankton, especially Brach- onus and an occasional Asplanchna, have been heavily parasitized internally by small sac-like bodies, often pear-shaped, with the smaller end attached to the lorica, or of spherical or flattened form. They occur in such numbers at times as to be a menace to the rotifer population. They are usually most abundant in any given species at the time of, or subsequent to, its maximum occurrence. It £15 - was not unusual to find as high as ten or fifteen per cent. of the individuals parasitized, and a number of empty loricee bearing addi- tional testimony to their destructive agency. Bertram (92) describes these structures as “parasitische Schlauche”’ in the body cavity of rotifers, and Przesmycki ('01) works out their life history, and describes the organisms as Dime- rium hyalinum, but does not designate their systematic position or affinities. There are, however, marked suggestions of sporozoan affinities in the organism found in the rotifers of the Hlinois plankton, which seems to be identical with that described by Przesmycki (’01). Obviously it is difficult to take a census of such internal para- sites. A record was kept, however, of the number of parasitized individuals in each species of rotifer, and references will be made to these results in the discussion of the hosts. Dimerium appeared in both summer and winter rotifers, and its seasonal distribution naturally depends upon the number of available hosts. It was in consequence most abundant during the midsummer and autumn months. CHE WATEA: Average number, 15,812,346, including filter-paper collections. If these be excluded and the silk catches only averaged, the number will fall to less than a tenth of this sum. The ciliates are found in the plankton of the Illinois throughout the whole year, and as a whole they do not exhibit any common seasonal predominance. The analysis of the distribution of the individual species which follows, exhibits two diverse tendencies which affect the distribution of the totals. These are the vernal and autumnal pulses of the Tintinnide, represented by Codonella cratera and Tintinnidium fluviatile, and the autumnal-winter occurrence of a large number of species during the height of the sewage contamination and bacterial development. The dominant species in this ciliate wave are Carchesium lachmanmt, Epistylis, Amphileptus, Lionotus, Plagiopyla nasuta, Glaucoma seintillans, Stentor niger, and S. ceruleus. Some species, as Halteria grandinella, have a wider seasonal distribution, and others, as Vorticella, Trichodina, Zoéthamnium, Pyxicola afjinis, and many others, are adventitious in the plankton. Still others, as Rhabdo- styla, Cothurmopsis vaga, Opercularia, and similar peritrichan parasites, are passive members of the plankton. The actively (9) 116 limnetic ciliates are very few. As such we may include Codonella cratera, Tintinnidium fluviatile, and possibly Stentor niger. Car- chesium lachmanni and Epistylis enter the plankton only in the form of detached and often moribund zodids, and thus are not typical planktonts, though of quantitative importance in our plank- ton in the colder months. A large number of species not here reported occur in our collections made elsewhere than in the river channel, especially in places where the decay of large quan- tities of organic matter is in progress. This is not a condition normally found in the open water of lakes, though it may occur along their shores, where vegetation is found, or in regions of sewage contamination. In the waters of the Illinois, on the other hand, the current, combined with sewage and industrial wastes and the organic detritus from the richest of fertile prairies, provides a suitable environment, even in the open water, for the support of a ciliate fauna of a magnitude somewhat unusual in fresh-water plankton. This fauna is present also in the back- waters, but is less abundant there than in the river itself. These Species occur in greatest numbers of individuals in our plankton dur- ing the winter months at minimum temperatures, rising in November as the temperature falls below 50°, and declining again as it rises to this point in April. As shown by the bacteriological investigations of Jordan (00) and Burrill (02 and ’04), the bacterial pulse attend- ing the decay of the sewage and wastes at Peoria does not reach Havana during the warmer months (see table on p. 231, Pt. L.), but when temperatures pass below 50° in November the increase in bacteria is marked. The decay is less rapid at low temperatures, and the process is still going on when the water in the channel passes Havana during the prevalence of low temperatures, and the ciliates that thrive in such an environment abound in the plankton at that time. The temperature limits of these ciliates of the period of bacterial development thus seem to lie between 50° and 32°. An examination of the plankton in the river at several points between Peoria and Havana at intervals throughout a year, will reveal how far the component species of this ciliate fauna are governed in their seasonal distribution in the plankton at Havana, respectively, by conditions of temperature and by the state of sewage contamination. The work of Roux (’01) upon the Ciliata about Geneva would seem to DL a ee 1 wi indicate that many species of the fauna of stagnant water are more abundant in that region during the winter months. Owing to the difference in food conditions attendant upon the increase of sewage and bacteria during the colder months in the Illinois River, it is impossible to determine from the data at hand the relative efficiency of the two elements of temperature and food in regulating the seasonal occurrences of our ciliates. Here, as elsewhere, the disastrous effect of sudden floods can be traced. The number of ciliates (Table I.) drops as floods rise, and recovers as the waters fall again. For this reason the winter occur- rences of the total ciliates are subject to considerable disturbances in the winter floods of the several years. The combination of the two methods of collection and of the two groups of ciliates, typical and adventitious, causes further irregularities (Table I.) in the sea- sonal distribution of totals. In the Illinois River, for reasons given above, the Ciliata occupy a place in the economy of the plankton of more than the usual im- portance. They feed principally upon bacteria, decaying organic matter, and the smaller alge, and are themselves eaten by the rotifers. J have found no evidence that they are utilized by the Entomostraca. They thus become active agents in the reduction of sewage and in the destruction of the bacteria of decay, in the purification of sewage-laden waters, and in the transfer of the matter in sewage to higher forms of animal life. The ciliates found in the Illinois include all the important species reported in the plankton of fresh water, and the list is somewhat larger than hitherto recorded in quantitative plankton collections in river or lake waters. These organisms escape readily through the silk net by reason of their small size, and in some instances the larger species, by reason of their mobility and flexibility, escape through the silk where less motile organisms of equal size are re- tained. By experiment I have found that well-shrunken silk bolting-cloth whose meshes average about 30-45 » will not retain Paramecium whose diameter is 40-70. It may be that supple- mentary methods of collection which will correct the error of leakage will show that the Ciliata are of wider occurrence in the plankton than has hitherto been found to be the case. 118 DISCUSSION OF SPECIES OF CILIATA. Amphileptus spp.—Average number, 630. Amphileptus is a well- defined winter planktont in the river at Havana, and it affords a striking instance of the interdependency of organisms in the plank- ton. It feeds upon the heads of Carchesium lachmanmt, engulfing the head in situ and encysting during digestion. Such heads, joined to the colony or free in the plankton, have been found in our waters. Its seasonal distribution at Havana is almost identical (Table I.) with that of Carchestum, upon which it feeds. Thus in 1897-98 Car chesium was continuously present in the plankton from October 26 to May 10, with a pulse,on December 7 of 283,800, and one on February 8 of 197,600. Amphileptus appears October 26; continues, with interruptions, to May 17; and has pulses December 7 and January 25, the latter reaching 13,545. In 1898-99 both appear early in October and have coincident pulses on November 22 and January 24. In 1895-96 the interdependence is even more striking, Carchesium reaching a greater development in this winter, with a pulse of 964,600 on November 27, and Amphileptus reaching 14,469 on this date and 14,835 a week later. Both species decline during the flood which follows, and rise during March to culminations, on the 24th, of 104,535 and 3,636, respectively. In 1898, Ampluleptus disappears on April 12 at 52°, save for an isolated occurrence May 17 at 64°. It does not reappear until October 18 at 52°. In 1897, it reappeared October 26 at 59°, and in 1895-96 its limits were 45° and 48°, with the exception of one occurrence, April 17, at 66°. Carchestum occurs irregularly and sparingly during summer months, and Amphuileptus was not taken in the plankton during that period. Its occurrence in the plank- ton is limited in the main to temperatures below 50°, but this limitation may be due primarily to the reduced numbers, at higher temperatures, of the organism upon which it feeds. It appears during the period of greatest sewage-contamination and bacterial development in the river at Havana. Roux (’01) finds Amphilep- tus most abundant in stagnant waters about Geneva in the winter months. Aspidtsca costata (Duj.) Stein.—Found in the plankton but once —Jan. 11, 1898, at 32°. Bursaria truncatella O. F. Mull.—Average number, 23. This large ciliate was found in the plankton at irregular intervals and in 119 small numbers. It was found six times in March; twice in January and April; and once in February, July, and November. Its ap- pearance in the plankton is thus predominantly in winter months and at temperatures below 45°, though it occurs in the extremes of temperature conditions. Carchestum lachmannt S. Kent.—Average number, 26,546. This is normally an attached species, and its appearance in the plankton is due to the detachment of the heads. Small fragments of colonies are also found, but the greater number are isolated heads. The detachment seems to be a physiological process of the organism and not merely the result of accidents. It is thus a detached and an adventitious planktont. Many of the heads taken in the plankton are in a moribund condition. For example, in a pulse of March, 1896, the following proportions were recorded. Total Date Carchestum | Per cent. | Per cent. perm.3 | normal | moribund 1896 | | aE ESS 60,420 | 55 45 ke iscsi sad alone Glee be aye, 104535 48 52 SD). 3.5. Shep 5, Bt pee 47,571 | 53 47 La pa GS pee 16,688 |, 39 61 Enumerations were based on the total number of heads, both normal and moribund. The colonies are sessile, and adhere in vast numbers to any substratum furnishing a suitable place for attach- ment—submerged vegetation, brush, sticks, and fishermen’s nets. ‘The latter sometimes become so clogged with Carchesium and floating mats of Crenothrix and Beggiatoa as to break down in the current of the river. How far the number of free heads in the plankton is an index of the development of the species in the stream can not be determined from the data at hand. This species has been taken in the plankton in every month of the year, but its occurrences between the early part of May and 120 October 1—that is, above 60°— are irregular and the numbers few (Table I.). It is thus predominantly a cold-water planktont. Winter collections in 1894-95 and 1896-97 were too few to trace its seasonal movements. In 1896-97 it appeared November 5, rose to a maximum of 964,600 on November 27, and declined in the December—January flood (Pt. I., Pl. IX.) almost to extinction, but recovered during its decline to a minor pulse of 16,160 on January 30. It again fell off in numbers during the floods of February (Pt. I., Pl. X.), but rose during the decline of March to a maximus of 104,535 on March 17. Numbers become smaller and occurrences irregular after May 1. In 1897, Carchesium increased rapidly in late October to a small pulse of 13,200 on November 2, with a decline in the following fort- night, and a pulse culminating December 7 at 283,800, with subse- quent decline. The fluctuations during 1898 may be followed in Table I. The numbers increase during the slowly rising flood of January to a maximum of 197,600 on February 8 at 32°, and decline again during the more rapid rise (Pt. I., Pl. XII.) of the next thre weeks. Stable conditions in early March bring about a pulse of 89,600 on March 15, and numbers decline again to 2,400 as the flood passes its maximum in the early part of April. As the levels fall another pulse of 99,200 appears April 26, from which a descent to minimum numbers—which prevail during the summer—takes place within a fortnight. The floods, especially sudden ones, seem thus to interfere with the appearance of Carchestum in the plankton, while gradual rises, as that of November, 1898, are not so detri- mental. The table of bacterial occurrences (Jordan, ’00) in the Illinois at Havana and Pekin given on p. 231, Part I., indicates that the bac terial development consequent upon the sewage and industriah wastes of Peoria extends down the river to Havana during the colder months of the year. The occurrence of Carchestum in the: plankton is thus coincident with that of greatest sewage pollution) and bacterial development at Havana. Carchestum is much more abundant in the channel of the river, where sewage pollution is greatest, than it is in the adjacent backwaters. It seems probable that the bacteria either directly or indirectly contribute towards its’ development, constituting, it may be, an important element inits food.! Flood waters, which dilute the sewage (cf. hydrograph and chlorine; | 121 in Pl. XLV. of Part I.) might for this reason tend to interfere with the development of Carchesium, and thus cut off the source from which the plankton individuals arise. I am not able, however, to trace any close correlation between the fluctuations of the chem- ical matters indicative of sewage and sewage decay and those of Carchesium. In the stable hydrographic conditions of 1897 we find a symmetrical pulse of considerable dimensions rising from 2,200 on November 9 to 283,800 on December 7, and declining to 26,500 on January 11, 1898. Stable low water with an ice blockade (Pt. I., Pl. XI. and XII.) characterize this season. No explanation for the fluctuation is suggested in the physical environment. The chemical condition of the water, was, however, greatly disturbed fee Pl XUIV.). The fivefold increase in free ammonia is indic- ative of approaching stagnation under the ice, and the threefold increase in chlorine marks the sewage concentration. Approaching stagnation might have caused the decline of Carchesiwm, or it may be a specific reproductive cycle of the organism which combines with the external factors of the environment to produce such a wave of occurrence. ; Chilodon cucullulus Ehrbg.—Average number, 102. This species was found in the plankton in January and February during the bac- terial increase. It was also found in July. It escapes through the silk net, and does not ordinarily appear in plankton collections, though abundant wherever decay is active. Codonella cratera (Leidy).—Average number, 101,024 or 452,500*. This is the most abundant of the ciliates in our plankton, consti- tuting about one third of their total number. It appears in every month of the year, and in 1898 it was recorded in every collection but one, that of December 13 (Table I.). It is sub- ject to great fluctuations in numbers, its maximum occurrences tend- ing to appear in April, May, or June, and again in September or October. Minimum numbers prevail during the winter, when many of the shells are empty, and the midsummer interval is subject to pulses of varying amplitude. Spring pulses were detected as follows: im 1895, on April 29 (16,324) at 64°; in 1896, on April 24 (562,152) at 72°;in 1897, on April27 (470,000) at 60°; and in 1898,0on May 3(736,000) at 60°. These vernal pulses coincide with or approximate closely to the dates of the spring volumetric pulses. This somewhat remark- able approximation of dates near the end of April may be the result, 122 in part at least, of the dates of collection; but after allowance is made for this, the species still exhibits a seasonal cycle of remarkable regu- larity. The autumnal pulse is of less amplitude, and of less regu- larity in location as to time and temperature. In 1894 it appears September 4 (14,000) at 78°; in 1895, on September 12 (5,840) at 81°: in 1896, on August 29 (58,800) at 74° or October 14 (63,200) at 57°; in 1897, on October 5 (204,400) at 71°; and in 1898siem September 27 (92,800) at 73°. The midsummer pulses are, as a rule (Table I.), of less amplitude than the vernal or autumnal ones. In 1896 and 1898 exceptions to this statement appear in two large developments which follow in each case upon the decline of the June rise. In 1896 (Pt. 1., PEae this pulse (152,400) came June, 11, and in 1898 (Pt. 1., Pl. XTi came (1,499,200) June 7 at 78° and exceeded in amplitude the re- corded vernal pulse. In both cases the pulse was recorded as occur- ring at an interval of a week after the crest of the June rise had passed. The character and sequence of these pulses is well shown in Table I. The occurrence of Codonella in abundance in the purer backwaters and in the plankton of our Great Lakes (Kofoid, ’95) indicates that it is not dependent upon the sewage bacteria directly for food for its development in our waters. The appearance of the greatest pulses during a period of considerable sewage dilution still further indicates its independence of sewage bacteria. A comparison of the fluctua- tions of the totals of the chlorophyll-bearing organisms with those of Codonella affords some evidence of a correlation between the two. Of 39 pulses which can be traced in our records in the chlorophyll- bearing organisms, 21 precede and 13 coincide with those of Codo- nella, while in the remaining 5 instances the multiplication of Codo- nella precedes that of the phytoplankton as a whole. Thus in the main the pulses of Codonella follow, or coincide with, those of the phytoplankton. The evidence of this sequence may be followed in Table I. by a comparison of the records of Codonella with those of the total phytoplankton. The sequence indicates that the food of Codo- nella may be found in the phytoplankton, and that these recurrent periods of growth have some connection with the conditions of nu-’ trition. The seasonal cycle of Codonella is closely followed by the other member of the family found in our plankton—Tzntinnidium fluvratile. es Codonella occurs throughout the whole range of temperatures. The winter minimum and the decline during the maximum temperatures of summer, combined with the presence of vernal and autumnal, or late summer, pulses, indicate that the optimum conditions for this organism lie neither in winter nor in summer. The spring pulse was at temperatures of 60°-72°, and the autumnal one at a wider range of 57°-78°. Permanent increase in numbers does not begin (Table I.) until March 15 at 46°,and the permanent falling off is found on November 15 at 41°. The optimum temperatures in our waters thus lie near 60°-70°, and conditions favoring growth are limited to a range of 10°-15° upon either side of the optimum. This species readily escapes through the silk net on account of its small size and its motility, and such collections give at the best in- complete evidence of its seasonal distribution. The amplitude of its fluctuations is thus reduced, and owing to the irregularity of the error arising from leakage, the reduction 1s not proportionally distrib- uted throughout the year. Tests made of the loss of Codonella by leakage through the silk indicated that but one was retained to twenty-fourfoundin the filtrate. Codonella was counted in both the silk and filter-paper collections, with the result that in 1897 the totals for the year (omitting one date on which the filter collection contained an unusually large number of Codonella) showed one Codonella in the silk to twenty-five in the filter collection. In 1898, however, the ratio was one to four and a half. The error in the filter collection is large, but data seem to justify the conclusion that only a small proportion of the Codonella is retained within the silk net. The proportion for the whole period of collection by the two methods (August 3,’97, to March 28,’99) is one to seven, if one date on which aberrantly large numbers appear in the filter collections be omitted. This species is a typical planktont, and is apparently the same as C. lacustris Entz, by which name it is designated by European writers. Leidy’s name, however, has priority according to the accepted rules of nomenclature. It is an exceedingly variable organism, at least in the form, proportions, and size of the shell, in the degree of its con- striction, and in the foreign particles which fill its matrix. The rings or bands which ornament the orifice vary in their number, width, and relative proportions, and in the perfection of their development. The intergradation which these variants exhibit is sufficient to my mind to make their elevation to specific rank unjustifiable. 124 Codonella is an important element in the food of many of the lim- netic rotifers, especially Asplanchna. Codonella is a common constituent in the plankton of our own Great Lakes (Smith, 94; Kofoid, ’95; Jennings, 00a), and has been reported from most European waters. Apstein (96) finds in German lakes major pulses in spring ahd autumn and minor ones in midsummer. Lauterborn (’94) reports Codonella in the plankton of the Rhine, and Schorler (00) in that of the Elbe, but neither follows its seasonal history. Coleps lirtus Ehrbg.—Average number, 13. This species occurred in the plankton collections irregularly and in small numbers, princi- pally in autumn months during the height of the bacterial deve ment. It escapes through the silk Aan Colpoda cucullus Ehrbg*.—Average number, 9,615. This species appears in the plankton wine aly during the colder months of bacterial predominance, from November to April, and occasionally during the summer. Cothurmopsts vaga (Schrk.) Blochmann was found in both 1898 and 1899 on Canthocamptus. Didinium nasutum (O. F. Mill.) Stein*.—Average number, 12,692. This species also is found in the plankton during winter months, especially in November and December during the bacterial increase. It was also found in midsummer. Epistylis spp.—Average number, 2,020. The free heads or frag- ments of colonies of one, or possibly of several, unidentified species of Epistylis, or it may be of Opercularia also, were associated with Car- chesium lachmanni in the plankton during the colder months, but in much smaller numbers (1 to 13 in 1898). Identification in most cases was impracticable, though in some instances FE. flavicans Ehrbg. was determined, and it seems probable that most of the winter forms at least belong to this species. Hempel (99) reports E. plicatilis on snails, and various other aquatic animals have been found infested — with colonies of undetermined species of Epistylis. : The distribution of Epistylzs in the plankton (Table I.) is in its” limits somewhat like that of Carchesium. It is more abundant and ; more continuously present during the period from November to June © (at temperatures below 60°) oa in the intervening warmer months. — It is found throughout the whole range of temperatures. Its pulsed f coincide with those of Carchesiwm when they occur, but they are not © : 4 125 always found in Epistylis when they appear in Carchesium. This degree of similarity in the seasonal cycle of the two genera is indica- tive of their correlation with the same environmental factors, the principal one of which is the increase in bacteria attending the colder months. Euplotes charon (O. F. Mill.) Ehrbg. was taken but once in the plankton—August 23, 1898. Euplotes patella Ehrbg*.—Average number, 2,888. It was found in small numbers and at irregular intervals from April to December throughout the full range of temperatures. It was most frequently taken in the summer. Glaucoma scintillans Ehrbg.*—Average number, 39,615. This species was taken in the plankton from the middle of October till the middle of April. It was present in larger numbers and more contin- uously in December and February. It is thus a member of the plankton during the time of bacterial increase. Halterria grandinella O. F. Mull.*—Average number, 255,769. The seasonal distribution of this species in the plankton does not show the limitation to the winter months noted so frequently in other . ciliates. It was found in every month of the year but May, in largest ~ numbers in July and August, and most continuously in December and January. The data are too few and irregular to determine any pre- dominance as to season or temperature. Holophrya simplex Schew. was found in-small numbers in the filter collections of December, February, and March in the winter of 1896-97 at temperatures from 32° to 44°. Leucophrydium putrinum Roux.—Average number, 525. This species was recorded July—September, 1898, during the low-water period, at temperatures from 89° to 63°. It was described by Roux (99) from stagnant water, but in our plankton no conditions of stag- nation attend its presence, though sewage contamination is great and decaying organic matter abundant. Lionotus spp.—Average number, 94. With Amphileptus in the winter plankton there occur a number of other, smaller, gymnostome ciliates which in best-preserved specimens resemble Lionotus. A few occurring in March and April, 1898, were found to be L. fasctola Ehrbg., and it is probable that most of the individuals belong to this species, though exact identification is difficult with plankton mate- rial. The seasonal distribution of Lionotus coincides very closely 126 with that of Amphileptus. The species appear in November or De- cember and continue through March in temperatures below 50°, but the numbers retained by the silk net are too small to trace their sea- sonal routine. Their seasonal distribution in the plankton coincides with the period of greatest access of sewage and bacterial increase in the river at Havana. Roux (01) finds this genus well represented in the fauna of swamps, and most abundant in October and March. Loxodes rostrum Ehrbg. was identified but once—March 22, 1897, at 44°. Nassula rubens Perty occurred July 30, 1897, at 84°. Opercularia articulata Goldf.—This species is parasitic upon aquatic Coleoptera. In the plankton of June 28, 1897, eleven colonies or fragments of a colony were found, the largest with 115 zooids. Opercularia nutans (Ehrbg.).—Average number of zodids, 60. In the plankton this species was found attached to Alona affimis in January, 1898, and to Cyclops in April and August. Opercularia not specifically determined were found free in the plankton in June and July; in November, attached to Canthocamptus ; in January, attached to Brachionus—and even to the eggs of this species. An unidentified form was also found upon Cyclops. Ophryoglena atra Lieberk.—Five irregular occurrences of this Species in small numbers were recorded in 1899 from January to the middle of March. Paramecium spp.—Average number, 41. Paramecium was found 18 times in the plankton. Two of these instances were in May and August at temperatures of 64° and 79°, and the remainder were between November 20 and March 30 at temperatures below 48°. Most of the occurrences are in midwinter at minimum temperatures under the ice. P. aurelia (O. F. Mull.) has been found in the river waters (Hempel, ’99), but not all taken in the plankton belong to this species. Specific determinations are not easily made with accuracy in preserved plankton material. In our plankton, Paramecium is present principally during the period of greatest contamination by sewage. : Plagiopyla nasuta Stein*.—Average number, 1,181,000 during the winter of 1898-99 from November 29 to March 28. This species was not recognized in the plankton of previous winters. It reaches a pulse of 11,520,000 on January 3, 1899, at 32.2° under the ice. Se ae Levander (94) finds it in numbers under the ice in Finnish waters. On account of its motility and small size it readily escapes through the silk net. Pleuronema chrysalis (Ehrbg.) Stein—Average number, 9. Re- corded only in January, 1898, at minimum temperatures. Prorodon farctus Clap. and Lach.—-Only a few scattered occur- rences—from the last of September to the first of March at tempera- tures from 73° to minimum. An unidentified species of Prorodon was also found irregularly from November to April. Pyxicola affims S. Kent.—Average number, 58. This species is usually attached to aquatic plants, especially to Lemna. It has been found in the summer plankton from June to August during maximum temperatures, especially in 1896, when recurrent floods brought much Lemna from the backwaters into the river. It was found October 18 at 52°, attached to Melostra varians. Rhabdostyla spp.—Average number, 110. Peritrichan ciliates re- ferred to this genus have been noted on Cyclops, Canthocamptus, Oligocheta, and even in considerable numbers upon the body, append- ages, and eggs of Polyarthra platyptera. They have appeared thus passively in the plankton during winter months from December to March, especially in 1899. Stentor ceruleus Ehrbg.—Average number, 882. This species presents a characteristic seasonal distribution in our plankton. Its numbers are never very large, and its full cycle can not always be traced in the records. It isa planktont of the colder season in our waters. But three records—one July 28, 1896, at 82°, one August 3 of the same year at 80°, and a third, August 15, 1894, at 84°—lie outside of the period between September 1 and May 1. In 1898 (Table I.) the autumn cycle begins September 6 at 79°, but in both 1895 and 1897 the species does not appear until late in November or in December at 34° or below. In years prior to 1898 the numbers were small and irregular, but on January 21, 1898, the maximum number of 28,800 was reached at 34°, under the ice, during the slowly rising flood of that month (Pt. I., Pl. XII.). It accompanied an increase in Stentor niger, and there are indications elsewhere that the two species may fluctuate together. The high (Pt. I., Pl. XLV.) chlorine (38.), nitrites (.175), and free ammonia (4.6) at the season of greatest development in the plankton are in- dicative of conditions approaching stagnation. The appearance of 128 this species in stagnant water has often been observed. Roux (01) finds it especially abundant in September, October, and February in stagnant waters about Geneva. Stentor niger Ehrbg.—Average number, 3,124. In our waters this species also is a winter planktont (Table I.). There have been but four records of occurrence between May 1 and September 1. In 1895-96 the species appeared November 14 at 44° and reached a maximum of 68,635 December 18, after three weeks of minimum temperatures and approaching stagnation under the ice. Numbers declined in the December—January flood (Pt. I., Pl. X.), but rose again in March, as the flood declined, to 39,087 on the 24th at 40°. It disappeared from the plankton April 30 at 70° and did not re- appear until November 17, from which time it continued until March 22. In 1897-98 it returned September 21 at 71°, attained a maxi- mum of 42,000 November 23 at 43°, declined during December, and rose to 47,000 on January 21 at 34° under the ice, and in the con- ditions approaching stagnation described in connection with the dis- cussion of S. ceruleus. A decline in numbers continued until April 12 at 52°. Favorable conditions for growth are thus found in our waters between 32° and 50°, and the optimum seems to lie near 40° or below. This species reaches its greatest development in our waters during the time of greatest sewage pollution and bacterial development. It is known as a bog-water species, and was found by Roux (’01) in stagnant waters about Geneva during the colder months. Hempel (99) reports this species as S. zgneus (7), but from the descriptions of Roux (01) Iam inclined to consider it as S. niger Ehrbg. It may be that both species are included in our data, but they are predomi- nantly of the m1ger type. They include also individuals of the black- ish variety S. zgneus var. fultginosus Forbes, which, it would seem from Roux’s description of these species, should be transferred to S. niger. The fuliginosus form was very abundant in the margins of Pine and Round lakes, Michigan (Kofoid, 95), during the summer in surface temperatures of 61°-70°, where sewage contamination was but shght. Stentor polymorphus (O. F. Mull.) Ehrbg. was found sparingly in July and August during maximum temperatures. Hempel (99) reports S. barrettt Barrett and S. roeselaa Ehrbg. from the river, but 3 I have not identified them in the plankton collections. = A le wae 129 Strombidium viride Stein was found in small numbers in January— March, 1899, at minimum temperatures. Stylonychia mytilus (O. F. Mill.) Ehrbg.was found in the plankton sparingly from September to February, and once in June. Tintinnidium fluviatile Stein.—Average number, 22,590 or 1,640,- 192*. This species is somewhat sharply limited to the warmer months in its seasonal distribution. In 1898 (Table I.) it makes its appearance April 4 at 49°, reaches a maximum of 720,000 May 3 at 60°, and has three decreasing pulses; one of 104,000 on June 14 at 80°, one of 95,200 on August 2 at 79°, and one of 22,400 on September 27 at 73°, and disappears from the plankton October 18 at 52°. The records in previous years are more irregular, though traces of vernal and midsummer pulses can be found in the records. Filter-paper catches indicate that only one in eighty of this species is retained by the silk. They also locate the pulses as approximately coincident with those of the silk collections. _ Apstein (96) finds Tintinnidium to be a spring planktont with its maximum in April in Lake Pl6n, while Seligo (00) finds it in lakes near Danzig in the autumn, with a maximum in September. In our own waters in 1896 the autumnal pulse in August-September exceeds the vernal one. The gelatinous lorica of this species is subject to great variation in its size and proportions, and especially in the region about the aper- ture. A somewhat thimble-shaped form was described by Hempel (96) asT.2llinotsensts, the specific distinctions being based wholly on the lorica. This form intergrades with the typical lorica of T. fluviatile Stein, and should not in my opinion be given specific rank. Trachelius ovum Ehrbg.—Average number in 1895, 847. This— Species did not occur in 1898 but was rather common in November-— December, 1895, reaching a maximum of 10,695 on December 4 at $2.5°. Isolated appearances in small numbers in December and January of other years have been recorded. In our waters it is thus a winter planktont. Stagnation conditions under the ice were approaching (Pt. I., Pl. XLIII.) when the pulse of 1895 occurred in the Illinois River. Apstein (96) found it, however, in Lake Plén with a maximum in May—June, disappearing in the summer and returning again in November. Trichodina pediculus Ehrbg.—Average number, 1; in 1897, 874. This species is normally found upon Hydra, on the gills and skin of 130 amphibians, and on young fish. It appears in the plankton during the summer months in every year except 1898, a single record only being made in that year. The earliest record was on June 11, and the latest on November 31. The whole temperature range is practically included in these occurrences, though the species disappears within a few weeks after the temperature falls below 50°. It usually appears in small numbers and irregularly, and no pulses like those of typical plank- tonts can be traced. A free life in the plankton 1s apparently not its usual habit. Zacharias (00) has recently called attention to its appearance in the plankton in German waters. Vorticella rhabdostyloides Kell—Average number, 61. This little Vorticella is found attached in small clusters to Anabena spiroides and occasionally to other members of the phytoplankton. It is some- what common in the waters of Lake Michigan, but is rare in spring months in the Illinois River. Vorticella spp.—Average number, 7,843. At irregular intervals from April to November isolated individuals and small clusters at- tached to bits of debris in the silt were taken in the plankton. They were most abundant at temperatures above 50°. The irregularity in their occurrences indicates that they are adventitious in the plank- ton. Identifications of plankton material are impracticable except in strongly marked species. Hempel (99) has found V. campanula Ehrbg., V. mzcrostoma Ehrbg., and V. similis Stokes in the river and its adjacent waters. Zobthamnium arbuscula Ehrbg.—A few colonies were taken in August and September in 1896 in the plankton, probably adventitious during the disturbed hydrograph of that year (Pt. I., Pl. X.). : The preceding list of 45 species does not complete the catalog of the ciliate constituents of the plankton, though it includes all of the species of quantitative importance during the years of our operations. The residium of unidentified ciliates, which, excluding the partial identifications in the above list, does not often exceed two per cent. of the total individual ciliates, includes principally isolated individ-— uals of species difficult of identification or others whose preservation did not permit it, and a considerable number of small ciliates and of forms ectoparasitic upon Entomostraca and other planktonts. Most of these organisms are either adventitious or passive members of the plankton, and further study of the littoral region, of stagnating Tiare: soul waters, and of these parasitic forms will reveal the great richness of the ciliate fauna in this aquatic environment. SUCTORIA. Average number, 332. This class is not quantitatively im- portant in the plankton, being represented,in so far as our records go, only by adventitious or passive planktonts. No limnetic species has as yet been found in the Illinois. An examination of the littoral region durirg the prevalence of ciliates will probably yield a rich suctorian fauna. DISCUSSION OF SPECIES OF SUCTORIA. Acineta linguajera Clap. and Lach.—This species is usually found on aquatic Coleoptera. = 000‘TS FI 99d | 00S ‘SF 6 “AON | 008°0S4°T! ZI “390 |000' £0" ¢| 2 -3deg | ———- .|| ————._ | 00%‘ S67 | tz 4m[ | Lest 008 600, €6 es Or9‘6TT | 9% Sny | OFO'S6T | OT ATHL | 9681 O8h PLT‘ TI TT “99d | 489‘667‘T| 47 “AON F88 ‘08 ZT 3dag jost‘¢e90‘T| zt ‘8ny | o0L‘0e9 | 9 Amt | sest SPs‘ lo Ly “320.| ———_ | ———_ 670 16e | st ‘sny |.—— | ———" | 76st ‘ON 97eq ‘ON a1eq ‘ON a7eq ‘ON a1eq ‘ON a1eq ‘ON aqeq Iva x Ne) si OGS-18" Ik JUN O00. S41 1 TL “dom Oce se ar elk oes 006 °9€9' tl tz29unf | 000 Srz's| ¢ AeW | ——— | ———-_| O8P‘set | zz zeW | ——— | —— | ZT0‘6T | Se wef | gest Oso‘ Tro‘ T| sz Ae | ——— ———— | ——— | —— | —— | ——_ | ——_ | ——__ | L681 | ora‘ ort SO, Gey Gl sSiG Sy OOF‘ zzz | 41 eunf! TIr‘s6z | 8 AeW | srs‘Frs‘s| Fe sdy | ——— | ——— | ——— | —— | zoe‘sz | 9 ‘wef |x968T —— 5 | ———_ | ———_ — | sto‘99¢ |6z ady | ——— | ——— | ——— ee CORI F68t ‘ON ayeq “ON ayeq ‘ON ayeq ‘ON ayeq ‘ON ayeq ‘ON ayeq Ivo “SOO ONIGCOATOXaA ‘VNIOTG dO SASTNd . 147 the seasonal distribution of individual species and these recurrent plant pulses will be discussed in connection with the various species wherever the data are available. For the present it will suffice to call attention to such correlation as exists between fluctuations of the phytoplankton and the total Plotma. The table on the preceding page gives the location and amplitude of the maxima of the ploiman pulses, and a graphic presentation of the seasonal curve of distribution of the total Rotijera will be found in Plates III. and IV. On comparison of the ploiman pulses with those of the chlorophyll-bearing organisms, graphically presented in Plates I. and I1., it will be found that 15 of the 33 pulses of Plovma contained within the period covered by the plates coincide in location with the plant pulses; that 12 follow at the next collection, usually a week later, and 3 within a fortnight; while only 3 of the 33 exhibit no such correlation. The data suggest strongly the agency of the plant pulses in building up the Ploiwma, and that the food relations are fundamental in the fluctuations of these planktonts. DISCUSSION OF SPECIES OF PLOIMA. Anurea aculeata Ehrbg.—Average number, 1,839. In 1898 this species has a very well-defined and characteristic seasonal distribution (Table I.). It first appears March 8 at 37°, increases to a maximum of 45,200 on May 10 at 61°. then declines, and disappears June 14 at 83°. The curve of its occurrence in this year is a very symmetrical one. It reappears on December 27 at 32°, and there are scattered occurrences through the winter months of 1899. Records in other years suggest in the main a similar distribution. In 1896 it first appeared January 6, rose to a pulse of 6,550 on May 8 at 76°, and, on the decline of the June rise, there was a second and larger pulse of 29,600 on June 17 at 76°. It reappeared on Decem- ber 29, and in 1897 reached a vernal maximum of 22,400 on May 25 at 66°, then disappeared, and was not again noted in the following winter nor until March 8. In 1894 the last vernal record was made June 12, and on September 4, at 78°, there was an autumnal pulse of 13,825—a phenomenon not repeated in subsequent years. The normal course of its seasonal distribution in the river plankton seems to be as follows: reappearance in December when minimum temperatures have been reached; slow multiplication during the winter, and a well-defined pulse on the decline of the spring flood in (11) 148 April-May with the possibility of a second on the June rise; and prompt and complete disappearance when maximum summer tem- peratures are established. Low water in the autumn seems to inter- fere with an autumnal pulse. In 1894 there was a well-sustained rise in September (Pt. I., Pl. VIII.) and a pulse of A. aculeata. In 1896, however, no pulse occurred in the high water of the autumn. No midwinter occurrences followed the very low water of 1897. It is thus in channel waters a vernal planktont, with its temperature optimum near 70° but below the summer maximum.” Hempel’s statement (99) that it is a “winter species’ is borne out by its presence from December through the winter, but its numerical distribution ranks it at once with the vernal organisms. Lauterborn (94) finds it abundantly in winter months in the Rhine, and Ap- stein (96) speaks of it as a ““Sommerform,’’ absent from Lake Plén from November till March, and with maxima from April to July in different bodies of water where it continues through the summer and till October, and then disappears. Summer temperatures in these waters, however, are not recorded by him above 21° C. (69.8° F.), which is about the temperature at the time of the vernal maxi- mum in the Illinois, and at least 10° F. below that of the summer maximum in our waters. Jennings (94, ’96, and ’00) records it as abundant in the summer plankton of Lake Erie, Lake Michigan, and some inland lakes of Michigan. These waters also are somewhat cooler (5°-10° F.) than those of the Illinois River in midsummer. Temperature, it seems, must have a decided effect upon the seasonal distribution of this organism in our waters, though the chemical conditions and food supply may also enter as factors in the summer suppression of the species. Females carrying usually a single egg appeared in 1898 early in April, and were most abundant during the maximum of the pulse. On an average, less than a fourth of the females were ovigerous. Empty loricze appeared May 10 (4,800) and 17 (3,200) at the crest and decline of the spring pulse, and the same phenomenon of deca- dence was noted in previous years during this period. Outbreaks of parasites were not recorded for the species, and the decline is to be attributed to cessation of reproduction and to the death and destruction of the individuals by the more usual causes. This species is quite variable, but no effort was made to follow its seasonal history. The type form is by far the most abundant. — 149 A. aculeata var. valga Ehrbg. was seen frequently. A. serrulata Ehrbg., regarded by Weber (’98) as a variety of A. aculeata, was recorded Jan. 24, 1899, and found by Hempel (’99) in December. It seems to be rare in our plankton. Forms approaching A. aculeata var. brevispina Gosse were also noted, but they, too, are rare, being recorded only in February and March, 1899. A. aculeata var. curvicornis Ehrbg. was noted April 29, 1896, at 70°. Anurea cochlearts Gosse.—Average number, 69,393, distributed as follows: A. cochlearis (sensu strictu) together with A. cochlearis var. macracantha Lauterborn, 9,421; A. cochlearis var. tecta Gosse, 15,432; and forms with posterior spine of intermediate length between cochlearts and tecta which include A. cochlearts var. stipitata _ Ehrbg., 44,540. Numerically this is one of our important species, containing over one ninth of all the rotifers in 1898. It is surpassed only by Brachtonus bakert (with varieties included), Polyarthra, and Syncheta. Average number of eggs, 32,358. This is a perennial planktont, appearing in every month of the year throughout the whole range of temperature. Its entire absence in August, 1898 (Table I.), is not paralleled in any other year. In 1897, for example, there is a well-developed pulse of 45,600 on August 24. In 1894, 1895, and 1896 there is a midsummer minimum of a few weeks’ duration in July, August, or September, but it is irregular in its location. While the appearance of sexual cycles was not traced by the records of males and winter eggs,—a matter of some difficulty and uncertainty in preserved plankton material,—the existence of such cycles is suggested by the recurrent pulses of occurrence in this species (Table I.). It is possible that the species is polycyclic in our waters. The pulses in 1898 are well defined, in fact, somewhat better than in previous years. The following table gives the num- bers in the pulses in the several years and the dates and tempera- tures at which the maxima occurred. All of the large pulses save those of November and December and one at the close of October (Oct. 25, 1898, 28,500) lie at tempera- tures above 60°. The vernal pulse of April-May is the largest and appears between 60° and 70°, and the amplitude diminishes as the period of maximum heat progresses, though in 1898 there was a recurrence of larger numbers as temperatures fell. The optimum 150 Putses oF ANURZA COCHLEARIS. Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 | ———— SSS June 12 78° 1,344 Sse 1895 | Apr. 29 64° 180,480 =a July 18 80° 17,805 1896 | May 8 76° 100,870 June 11 NEO 95,200 July 2 81° 12,800 a 28 81° 17,600 1897 | May25| 66° 620,800 July 21 g2° 37,600 1898 | May 10 62° 1,145,600 June 21 iii 372,800 July 19 84° 17,200 Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 | ———— | ———— —_ Sept. 4 78° 580 = 1895 | Aug. 21 83° 17,805 Sept. 23 76° 5a Nov. 20 44° 1,120 1896 | Aug. 21 79° 5,600 Sept. 16 ide 6,224 Dec. 29 Soe 3,840 1897 | Aug. 24 78° 45,600 Octwar> 70° 4,800 SS | 1898 Sept. 27 73° 54,400 Nov. 21 40° 10,000 . Oct. 25 48° 28,500 conditions seem thus to be found in the river at temperatures some- what below the maximum, between 60° and 70°. The phenomena of recurrent pulses are distinctly traceable in the seasonal distribution of this species, not only in 1898 (Table I) but also in preceding years. The large May and June pulses of 1898 appear on the declines of the spring and the June rise, respectively; the pulse of September 27 is in a falling river; and that of October 25, on a slowly rising flood (Pt. I., Pl. XII.). In 1897 (Pia XI.) the first two pulses attend the spring flood and June rise in like manner, but the two subsequent pulses are in stable low water. In 1896 five of the seven pulses le on the declines of the recurrent floods of that year and two in rising waters (cf. Pl. X. of Pt. I. and the table just given). In 1894 and 1895 the pulses appear either in falling water or in the earliest stages of the rise. The number of pulses on declining waters is somewhat greater than the relative number of days of this condition would lead us to expect, and it seems probable that optimum conditions for the appearance of larger numbers of Anurea cochlearts are to be found in such hydro- graphic conditions. The run-off of impounded backwaters is one of the favorable phases during flood decline. On the other hand. oe 151 the distribution of the pulses with reference to the floods and the appearance of pulses during rising water suggest the operation of other factors than the one arising from contribution from back- waters. The pulse must be dependent to a large extent upon food supply of the organism, and a correlation between its periods of multiplica- tion and the pulses of its food, the chlorophyll-bearing organisms, is to be expected. A comparison of the seasonal distribution in 1898 (Table I.) and the pulses of chlorophyll-bearing organisms (PI. II.) reveals the fact that three of the A. cochlearis pulses coincide with those of the plants constituting their food, and the other three coincide in part only, the remainder of the chlorophyll-bearing groups reaching their culmination a week prior to that of the rotifer. In 1897 the three pulses of A. cochlearis which lie in the common period (PI. II.) all culminate a week (in one case in part in fourteen days) after the maximum of the plants in question. In 1896, three pulses coincide and three follow in the subsequent collection; and in 1895, two coincide and two follow. Collections at daily intervals would be necessary to follow the correlation more accurately. It is probable from these juxtapositions and sequences in the A. cochlearis-algz pulses that we are dealing with a food relation. Multiplication of alge leads to increase of Anure@a, which, in turn, reduces the algz,and then itself declines until the food planktonts again increase. Anurea cochlearis is exceedingly variable in the length of the posterior spine, in the development and degree of curvature of the anterior spines, in the arrangement of the areas of the lorica, and in the degree of its ornamentation by small spinules. The separation of these varieties where every individual must be assigned to some one of them, is a matter of some difficulty owing to the presence of intergrading individuals. The characters which signalize var. hispida Lauterborn and var. irregularis Lauterborn are not quickly recognized under the conditions of rapid plankton enumeration, and no effort was made to trace their seasonal distribution in our plank- ton. Lauterborn’s var. macracantha was included with the type form—his var. typica—in our records. These two include those individuals with medium-sized and longer posterior spines. In our waters the variety macracantha is relatively rare, at least as figured by Lauterborn (’98). Indeed, both the type and this variety consti- 2 tute less than a seventh of the total representatives of the species. Their distribution throughout the year (Table I.) accords with the results obtained by Lauterborn (’98), who found that the average length of the posterior spine from January to May and from October to December was from 78 to 48 y, while from June to September it was from 28.5 to 21. In Table I. it will be seen that the longer- spined forms which I have referred to A. cochlearts var. macracantha and var. typica occur in the plankton from January to May 31, and then disappear, returning again, in small numbers, October 25. The short-spined variety referred by me to A. cochlearts var. stupitata and the spineless var. tecta are, on the other hand, continued during the summer. The natural result would be that the average length of the spines in the species as a whole would fall during the summer months. It is apparent that this tendency on the part of A: cochlearis to become shorter and smaller during the summer months does not bear out the contention of Wesenberg-Lund (98) that winter individuals are smaller and summer ones larger among perennial rotifers. He reports var. tecta as ‘‘die Hauptform des Winters” in several Danish lakes, and the variety with a long horn as a summer form, found in July—August. Of these varieties, macracantha, typica, and stipitata intergrade in our waters with numerous connecting links, while var. tecta is not connected with the other forms by many individuals with inter- mediate characters. Lauterborn (98) also notes the greater inde- pendence of this variety in the waters of the Rhine. In Table I. the seasonal distribution of these three varieties, the long-spined (typica and macracantha), the short-spined (sttpztata), and the spineless (tecta) are given separately. It will be noted that the long-spined form has the distribution above mentioned, that var. tecta runs throughout the whole year, and that var. stzpitata is absent in midwinter and isa common summer form. The relative numbers of the varieties fluctuate in different years. For example, var. tecta was relatively but one fourth as abundant in 1897 as in 1898. As shown in Table I., whenever coincidently present: in the plankton all the varieties respond to the causes which produce the rhythm of occurrence, the rise, culmination, and decline of the pulses being much alike in all of the varieties. About three eighths of the females noted in 1898 were ovigerous, carrying as a rule but a single egg. Instances of two eggs were bss noted, but they are rare. The greatest proportion of egg-bearing females appears during the rise of the pulse, as is seen in the follow- ing table, which gives the data of the vernal pulse in 1898. From ANUR-ZA COCHLEARIS. | No. of Ratio of Date | ovigerous Total Total | | eggs to No. of females females eggs | individuals dead joni 2 eee | 800 2,200 SOON eee Zaria 0 i 6,400 15,200 | 8,800 | i273 400 BOAO: Soe ee eee, 45,000 137,800 65,000 | pee Ab, 3,200 NOES? SG ae ier 536,000 . 1,022,400 | 552,200 IS ES) 9,600 May meee... .. | 489,600 1,145,600 643,200 | iN Sales 7s} 99,200 oo 110,400 434,800 160,000 1:2.71 | 100,000 2 2 | 6,000 RieMOONy war, 200% 122894 1,800 Many SING Spates ae rie | 3 , 000 1 e010) 3,400 | ILE Sys 4) 1,800 April 12 to the crest of the pulse on May 10 (not inclusive) the aver- age ratio of eggs to individuals was 1 to 1.87. From the crest to the foot of the decline inclusive the ratio is 1 to 2.98. The number of empty loricxe is given below, and it will be noted that on the week prior to the crest of the pulse there were 107 living to one dead; on the crest itself, one to twelve; while the week following the crest of the pulse there was an empty lorica for every 4.3 living females. Rapid multiplication thus attends the rise of the pulse and rapid destruction its decline. Parasites were very rarely observed in this species. The decline of a pulse is thus due to the cessation of reproduction and a relatively heavy death rate. Apstein (’96) finds that in Lake Plén Anurea reaches its maxi- mum in July and is at its minimum in April. It is everywhere common in the German waters. A. tecta, on the other hand, was found only in the smaller lakes and in great numbers, replacing cochlearis in warmer months to some extent. Lauterborn (’98) regards it as the most abundant rotifer in the Rhine. Our statistical records do not show that this is the case in the Illinois, for it is here 154 surpassed by several other species. Zimmer (’99) finds that this species is the most common winter rotifer in the plankton of the Oder, with a maximum in the spring and a predominance of var. tecta from July to September. “Schdrler (’00) finds it to be the most common rotifer in the Elbe—from April to November; and Skor- ikow (’97) finds it in the Udy, in Russia, throughout the summer in great numbers, but surpassed by Syncheta, Polyarthra, «and Brachionus angularis. The variety tecta greatly exceeds var. stipitata in these waters. Seligo (’00) finds it throughout the year in Prussian lakes near Danzig, with a maximum in May. There are indications, in his data, of recurrent pulses during the summer, but his interval of collection is too great to follow their history. Burck- hardt (00a) finds it throughout the year in Swiss waters, with its single maximum in August. Jennings (’94, ’96, and ’00) reports it in the summer plankton of Lake Michigan and Lake Erie and of inland waters of Michigan. Anurea hypelasma Gosse.—Average number of females, 2,390; - of eggs, 1,917. This species has a very definite limitation to a period extending from early in June to the first days of November. There are but two records outside of these limits—a single female and egg on Jan. 11, 1898, and another upon April 19 of the same year. The probabilities of occurrence in very small numbers at all tempera- tures is thus indicated. The following table gives the data of pulses and temperatures. All of the pulses save one occur at temperatures above 70°, and with this exception the species declines rapidly and disappears shortly after temperatures pass below 60°. It is plainly, in our waters, a summer planktont, with its optimum temperature close to the summer maximum. This species takes no share in the vernal pulse, and there is no satisfactory evidence of any fluctuation corresponding to it at any other season. There are three or four pulses in each summer, and the species is apparently polycyclic, for winter eggs were found in 1898 either at the maximum of the pulse or the week or fortnight following. Thus 24,000 winter eggs were recorded on Sept. 27, 1898, the date of the maximum of the Septem- ber pulse. The parthenogenetic eggs preponderate during the rise ~ of the pulses in a very marked manner in this species. For example, in this September pulse 55,400 eggs were recorded during its rise to 500 during its decline. In like manner, in the case of the a: air . 195 PuLses OF ANUR#ZA HYPELASMA. First record Pulses Year : a Date | Temp. Date | Temp.| No. 2 a ole SSR June 27 80° June 27 80° 1,200 LPT on glee IIE geen at eee ae June 28 (ise July 14 | 79° |10, 400 0S 2 eee June 14 83° June 21 (ike | 9,600 Pulses Last record Year = No Date Temp. No. Date | Temp. 1896 Aug. 15 SAS 2 ,000 ——— | ——— | —— | Sept. 30 58° ane 20 74° | 3,600 1897 Aug. 31 8024)|)20,000)\Oct.- 5 dele 23,200 | Nov. 2 so9 1898 Aug. 16 77° | 16,000 | Sept. 27 13. 43,200 | Nov. 1 45° Oct, 1s 52° 13,500 August pulse 15,200 eggs were found on the rise to 4,000 on the decline. The location of the pulses of A. hypelasma is of special interest. It will be seen in Table I. that they occur in 1898 in the same col- lections in which the pulses of the other species of Anurea and many other rotifers occur, or in collections but a week removed. They coincide in general with dates of the ploiman maxima noted in the opening discussion, and exhibit the same correlation with hydro- graphic conditions and intercalation with the pulses of chlorophyll- bearing organisms which were noted in the general discussion and have been found in preceding species. The comparison with Anurea of the cochlearis group affords a curious instance of an entire sup- pression (Table I.) of one species of a genus (cochlearis) in the month of August and the occurrence of a normal pulse in another (hypelas- ma). Comparison of the distribution of cochlearts in previous summers would lead us to expect a cochlearis pulse in August, 1898, 150: but none appears in this interval, while hypelasma runs a normal course of recurrent pulses throughout the summer. This August pulse of hypelasma (Table I.) culminates August 16, just a week after the symmetrical and well-defined pulse of chlorophyll-bearing organisms (Pl. IT.) of August 9. With a single exception, all of the pulses of 1896 and 1897, indi- cated in the table, fall a week later than, or coincide with, the pulses of chlorophyll-bearing organisms, as in 1898. This species has not occupied a prominent place in the hterature of fresh-water plankton. Weber (98) finds it rare in Swiss waters in the summer. Lauterborn (’93) classes it with the monocyclic summer forms in the plankton of the Rhine, though he states in a footnote that he had found winter eggs once in June. It 1s probably polycyclic in our waters. Skorikow (96) finds it in the summer plankton of the river Udy,in Russia, but it is not mentioned by other investigators of the potamoplankton of Europe. Apstein (96) does not report it from Lake Plon. Asplanchna brightwellit Gosse.—Average number, of adulke 2 ,O798 of eggs, 396; averages in 1897, 16,161 and 2,156. This is a poly- aye perennial planktont in our waters. It has been found in every month of the year, but the greater numbers and more con- tinuous occurrences lie between May 1 and October 30. In 1898 — (Table I.) all but 200 of the 108,120 recorded, lie within these limits, and all but 260 above 60°. In previous years approximately the same limits are found. The following table gives the data of pulses and temperatures. PuLses oF ASPLANCHNA BRIGHTWELLII. Year Date’ |Temp.| No: | Date |Temp.| No. US OF ore SR e Mee eran a ale en eyes aie te —————= | = | DOB eos ete sce eee ———— | —— | ——~— | June 19} 80° 6,678 1 ohS Oat Ae dE ee Meese 7 ot Mayet |,°702 -) 1-788) june 27 ste 1,600 TO OY 2 Reece ane Se drat rae Ph ee SSS | SS |_| OS | |S NOOB ye seis ate deen hae once, ecm a May 5 602/20, 300%) June 24)" 772 1,100 a ce 57 PuLsEs OF ASPLANCHNA BRIGHTWELLII—Continued. Year| Date “Temp. No. | Date Temp. No. Date |Temp.| No. Sel Ee eee | | | 1894 | July 30) 82° | 19,398 ae wl os “I bo On 1895 | July 29] 75° | 1,344 | Aug. 12] 79° [118,206 | Nov.14| 45° | 1, - | Aug.:21.|. 79° | 1,200 | 1897 | July 21| 83° | 3,200 | Aug. 10] 81° | 5,200|Sept. 9] 80° |284,000 | 1898 | Aug. 2| 79° | 23,200 | Aug. 23| 81° | 4,000 | Sept.27| 73° | 6,400 It will be seen from this table that all the pulses save one, and that one (Nov. 14, 1895) poorly defined, lie between 60° and the maximum temperatures, indicating an optimum near the summer maximum. There is in this species no prominent vernal pulse such as that found in Anurea, and the highest numbers were reached during the height of the warm season. The evidence of the polycyclic character of the seasonal distribu- tion of this species is shown in the following table, which gives the occurrences of ovigerous females, males, and winter eggs in 1898. It will be noted that ovigerous females are more numerous during the rise of the pulse; that the males appear just before, during, and after the culmination of the pulse; and that winter eggs are absent only during the rise of the pulse, and appear at or after its culmina- - tion and during the decline. The data given afford a fine illustration of the seasonal distribution of polycyclic rotifers,and of the relation of the sexual cycle to the number and character of the representa- tives of the species in the plankton. The growth of the pulse results from a rapid succession of parthenogenetic generations in the course of about two weeks, and it culminates with or shortly after a pulse in the food supply. The decrease in food supply is attended by the appearance of males and winter eggs, a decrease in ovigerous females, and a decline of the species. With the recurrence of the food supply the parthenogenetic cycle again begins. The same course of events is run in each recurrent pulse. Food supply rather than temperature seems to be the determining factor in this rhythm. 15S: ASPLANCHNA BRIGHTWELLII. faite Males | without eges,| teneleme Mayr cS eiicin ieee ene se eee rete ene O 3,200 12,800 Kasam tet UO) deters Ie Leson amican e Seienst Eee ace el 8 ,000 4,800 8 ,000 Teo SHEL sat g Aa Suze cars tata al Newel 1,600 5,600 4,000 Fe ALS hah eee cee eoe ores ae Sas Reeve che pasta == 400 O Pl een gta SO LS sega Mae Pen arr ne Gey ey na te ——— 200 0) AUTOS NT veya decreed laces et tens RSE ene eae a 200 0 Da eres a aR nL RCT, rteaas hare) 5 —— O O Pri eDalecticias Merit dreite Baya hues eae tag is hight oom eae 800 300 Se Di One ee yaa Ate a eee eeg oe LUI ar GE — 100 0) elie R Oh ef ccan a crohns apace eens ie ada — 120 40 Vaid LAC Sete erect ete Pee eet ee sy eRAEA <= 6) 0) TN NLLO) onetime eon as irr Rade a ae « —— 40 240 sl Ove eer Aiea ero emaghe apace sot tye cence 240 12,400 5,260 VAY DUCADIS At S/Aoars bud Guna Ung a Late Gera co: 4,000 7,200 12,000 J Oye Mee hat ira nity ar ep eee — 80 0 i INCL zen ON Geert oh oR werlece Serge, aa = 6) 800 e DSi at peti atee: AROSE EASON ee Secunia CALE — 3,200 800 Pete OR recep nie ei Sue ered Nan RT Sore — 1,600 800 De PLeRIber ON nts cuera Mile Bean eee — 0 0) e IERIE RG Nano tar eg ——. 0 0) i DOME itd nat fee eed tery ——. 540 600 ~ At EPROM TENT AER ieee ge: eI ——. 3,200 3,200 October Aus lieth vorteen a meer ane ney —— 500 0) CEN SP cen 2 LUN eee eD aa io 1,000 0 159 An examination of the location of the pulses of Asplanchna brightwellit shows (Table I.) that in 1898 one coincided with the pulse of chlorophyll-bearing organisms (PI. II.) and the remaining four followed it either in a week or fortnight. In previous years two pulses coincide with and five follow those of chlorophyll-bearing organisms, and a single ill-defined one (Nov. 14, 1895) precedes. This species is not wholly herbivorous in its feeding habits. Codonella, Difflugia, and even other rotifers such as Brachionus and Anurea, are frequently seen in the digestive tract. Diatoms, even Melosira and Pertdinude, as well as Pediastrum and other alge, are frequently taken asfood. Inone instance a Daphnia cucullata 300 p in length was seen in the stomach in a transverse position. It was fully a third the length of the animal which had eaten it. Asplanchna brightwellu is reported by Skorikow (’97) in the summer plankton of the Udy, in Russia; by Schorler (’00) as spo- radic in the Elbe in June and September; and by Lauterborn (’93) from the Rhine, where its cycle coincides with that of A. priodonta. Zacharias (’98) reports it in German reservoirs in June and August. It is a cosmopolitan species, but does not seem to have been found by other plankton investigators in European waters. Asplanchna ebbesbornit Huds.—Average number of adults in 1895, 942. In 1898, only winter eggs of the species were noted in the plankton in February, June, July, September, and October, though adults were doubtless there. Adults have doubtless oc- curred sporadically in all other years, and in 1895 reach a pulse of 21,518 on July 6 at 81°, which was followed by the appearance of males and winter eggs. All records of adults le between April 29 and September 14 and above 60°. This rare rotifer has not appeared in the literature of fresh-water plankton elsewhere to my knowledge. Hempel’s statement (’99) that his record of its occurrence in the Illinois is the first for this continent must be modified, since Leidy (87) found it near Philadelphia. It is evidently a summer plank- tont in our waters, and the wide distribution of its winter eggs suggests that it, too, may be polycyclic; and their appearance in the plankton in large numbers with reference to the adults taken, leads to the further inference that its center of distribution is prob- ably not in channel waters, and that it may be predominantly limicolous species, or have its center of distribution in the quieter backwaters. 160 Asplanchna girodi de Guerne is reported by Hempel (99) in the backwaters in April. Asplanchna herrickt de Guerne.—Average number, 15; in 1897, 295; in 1896, 317. This species was always rather rare in our waters, and is apparently a summer planktont. The earliest record is April 29, at 64°, and the latest, November 15, at 48°. There is an indication of a vernal pulse in April-May in 1896 and 1897, and the recurrence of the species at intervals of a few weeks during the sum- mer suggests a polycyclic habit similar to that of other members of the genus in our waters, but the data are insufficient to follow the cycles if such exist. Ovigerous females were present when numbers were greatest, and males and females with winter eggs were found at the time of the vernal pulse on May 25 (3,200) in 1897. Hempel’s statement (’99) of its rarity in June and July is not borne out by the statistical records in these months in 1896, 1897, and 1898. This rotifer is abundant in the summer plankton of Lake St. Clair, Lake Michigan, and lakes of northern Michigan (Jennings, ’94 and 796), and it may be significant that it reaches its greatest devel- opment in the Illinois in the spring at 60°-70° and not during the period of maximum heat. This is about the summer temperature ef those northern waters. This species has not to my knowledge appeared in the literature of European plankton, though it is found in European waters. Asplanchna priodonta Gosse.—Average number, 441; winter eggs, 7. This species is much less abundant in our waters than its associate A. brightwelli1, being outnumbered by it five to one in 1898. It is in the Illinois River a summer planktont only, at least so far as the records go, though reported elsewhere as perennial. The earliest record in any year is April 29, 1896,at 70°, and the latest October 5, 1897, at 70°, when an unusual pulse of 22,000 was found. The records are too scattered to trace the seasonal history. There are only indications of recurrent pulses. In May, 1898 (Table I.), the best-defined pulse is recorded. The details, which conform in the main to the sequence noted in A. brightwelli of ovigerous females with summer eggs during the rise, with males and winter eggs at and after the culmination of the pulse, are given in the appended table. This is the only cycle found in this year. The presence om ovigerous females and winter eggs at other seasons as well, in other 161 ASPLANCHNA PRIODONTA. { Females Females Females Total Date Males | without | with sum- | with winter | . Fi nee £ eggs mer eggs eggs individuals MMO ness cae. — | 3,200 —— ee eh P les 8 00 I Ser 800 10,400 3,200 == | 14,400 = | VARS Gin Ota eee nee 120 1,600 200 200 Ph 40) Meret fs we es a sk — 1,600 400 — | 2,000 years, leads us to infer that the species may be polycyclic in our waters. This limnetic rotifer figures largely in the fresh-water plankton of other localities, attaining a relative development greatly surpass- ing that thus far found in the Illinois River. Apstein (96) reports it of irregular occurrence in the smaller lakes of Holstein, and Seligo (00) finds it perennial in Prussian lakes, with maxima in April and September. Wesenberg-Lund (’00) also finds it perennial in Danish waters, with sexual cycles in May and September. Marsson (’00), in waters about Berlin finds a great variation in theseasonaloccurrence, but the intervals of his collection—four to six weeks—were too great to follow seasonal distribution satisfactorily. Zacharias (’98b) finds it in the summer and autumn plankton in a number of German lakes and streams. Zimmer (’99) traces its appearance in the Oder from February to a maximum in May, from which time until the end of July it is “einer der haufigsten Planktonorganismen”’ (!). It then declines, but returns in small numbers in November. Schorler (00) records it in the Elbe from April to October, with maxima in April-June and September. Burckhardt (’00a) finds, on the other hand, that in Swiss waters it reaches its greatest development from December to March with a maximum in January-February. There are also secondary maxima in May—June and in August. Lauter- born ('93) finds it to be a dicyclic perennial planktont in the Rhine, with maxima in April and September—October. A part of the great variation in the seasonal distribution of this species which is ap- parent in this survey of the literature may be due to insufficient collections or too great an interval between collections. The species 162 is probably a polycyclic planktont with its greater pulses in spring and fall. Asplanchnopus myrmeleo Ehrbg.—Taken in small numbers and irregularly from May to October at temperatures above 60°. Ascomorpha ecaudis Perty.—Found rarely in early summer, in temperatures above 60°. Brachionus. The discussion of the species of this genus in our plankton is fraught with great difficulty. The genus is represented in the Illinois River by a very large number of individuals (fully 25 per cent. of the total Plowma), and the species are, almost without exception, exceedingly variable. They are loricate forms, and the variations affect the proportions of the lorica and the development of its prolongations in spines, antlers, and various diversifications of its surface. They are evident upon the most cursory examination in most cases, and have been utilized by systematists for the estab- lishment of species. . For example, Weber (’98) lists no less than 67 species of Brachionus, the most of which he regards as synonyms, and he includes only a part of the species. Fuller knowledge of the extreme variability in this genus has led the most thorough students of the rotifers to regard many of these so-called species as but varieties at the best, and to express their opinion with unmistakable plainness that descriptions of new species among rotifers should only be made after most careful determination of the variability of the organism (cf. Rousselet, 02, Jennings, 00, Wesenberg-Lund, ’00, and Weber 98). . For one not a specialist in rotifers, the attacking of the Brachionus problem from the statistical standpoint is made difficult by the condition of the literature of the subject, owing largely to the semi- tropical distribution of the genus; by the absence of any critical monograph of the whole genus dealing fully with the synonymy of the subject; and by the necessity of establishing and maintaining constantly amid the ceaseless change of varying forms the same standards of distinction between the species or varieties into which all of the individuals enumerated must be assorted. Furthermore, these distinctions must be established before the plankton 1s counted; that is, before the limits of variation are fully appreciated. It is needless to say that my efforts are at best but approximations 163 to a satisfactory analysis of the genus in our waters. Brachionus contains by virtue of variation in the hard parts of its lorica most excellent material for the study of the problem of variation, and its rapid multiplication makes possible a correlation with seasonal and environmental changes not often afforded. Evidence has accumulated in the various papers of Schmarda, Ehrenberg, Barrois, v. Daday, Anderson, and others who have dealt with the microscopical fauna in tropical regions, that this genus attains its greatest development in the warmer waters. It is there- fore not strange that Skorikow (796) finds the genus well represented in the warm and shallow waters of Russia, and that the plankton of the Illinois River and its backwaters should contain a large and varied representation of the genus. For convenience in treatment I have arranged the individuals of _ Brachionus under the following species, without, however, intending to indicate thereby that they have equal claims for specific recogni- tion. The most of these include one or more varieties, and in desig- nating the varieties I have taken those forms—for example, in Brachtonus bakeri—whose descriptions most closely fit the predomi- nant varieties in our waters, designating them often without com- plete consideration of all synonymic possibilities. In some cases several possible varieties have been included under one head. The following is the list of species with the varieties which have been thus separately enumerated. Brachionus angularts Gosse, >" ae var. bidens Plate Zs bakert Ehrbg. 7 ‘var. bidentatus Anderson 3 ry “ brevispinus Ehrbg. clumorbicularis Skorikow melhemt Barrois and v. Daday obesus “‘ ts “a rhenanus Lauterborn tuberculus Turner budapestinensts v. Daday militaris Ehrbg. mollis Hempel i pala Ehrbg. (12) 164 Brachionus pala var. amphiceros Ehrbg. ‘i “2 =) orcas, Gosse ah fy partes “forma spinosus Wierz. quadratus Rousselet urceolarts Ehrbg. : * var. rubens. Ehrbg. . i . ‘“ bursarius Barrois and v. Daday vartabilis Hempel Brachionus angularts Gosse.—Average number of females, 57,890; of males, 25; of summer eggs carried, 29,560; of winter eggs, 1,223; of male eggs, 54. Of the individuals, 13,973 belong to var. bidens and 43,942 to the type; of the eggs, 2,035 belong to the variety and 28,802 to the type. The combined statistics of the species will be discussed before the type and variety receive separate treatment. This species was found in every month of the year and throughout the whole range of temperatures, but the period of continuous presence and large numbers lies definitely between May 1 and November 1 and above 60°. Infact, in 1898, 98.6 per cent. of all the individuals were found between May 31 and October 4 and above 70°. Approximately the same conditions are found in previous years save in 1896, when an earlier spring (cf. Pl. X. and XII., Pt. I.) is attended by an earhtes appearance of this species. ‘Temperature seems thus to have a very decided effect upon the seasonal distribution of the species, and may have something to do with its apparent absence in the cooler waters of our Great Lakes and of L. St. Clair, for in spite of all the work done upon rotifers in those regions by Jennings it has been found but once—by Kellicott (97) ina cove at Sandusky. This identification may be questionable, since he says “I at first took it for B. mollis Hempel.’ WNotops pelagicus, since described by Jennings (00), is found in the plankton of Lake Erie, and according to him this species is much like B. mollis in its appearance. In any event B. angularis is very abundant in our warm waters and practically absent in the more northerly waters of Michigan, whose summer temperatures are 10°-15° below that of the Illinois River and its backwaters. Brachionus angularts presents the usual phenomenon of recurrent pulses, but in spite of the large numbers they are rather less regular 78 oo, eo 165 than usual—for example, than those of Anurea (Table I.). This irregularity is somewhat more pronounced in the separated records of the type and variety (Table I.) than in their combined statistics. This fact that their combined curve of occurrence is more regular than their separated curves constitutes, to my mind, evidence that we are dealing only with one genetic cycle, and that the variety does not belong to a fully separated genetic series. The following table gives the data of pulses and temperatures in the several years. PULSES OF BRACHIONUS ANGULARIS INCLUDING VAR. BIDENS. Year| Date ‘Temp. No. Date |Temp.| No. Date |Temp.| No. == | | | ee uly 13] 82° | 226418 7395 | ———_ | _— | _____| July 6] 81° [399,196 | July 23| 80° [100,826 | me20)) May 25; 70° | 67,600 | June 17 | 76° | 60,800 | July 10) 80° | 51,200 | =H 2 8 ee Ae 25° «| 75.000.) July 211 83° |°70,400 1897 1898 | June 7| 78° | 4,800 | June 28| 78° [544,000 | July 19| 84° |335,600 Av’g | 36,200 269,776 103,924 Wear} Date |Temp.| No. Date |Temp.! No. Date Temp. No. | —— | ——— _| Sept.17| 73° 1,272 | ——— | —— | ———— SO? [585.00 | Awe, 29 |! BOP POS 7) |) <9) Sa> |) 20,800 | Aug. 21) 79° | 29,600 | Sept. 16, (ike SROs 80° |988,000 | Sept. 14] 83° |368,800 | Oct. 5 | 71° | 18,400 77° |353,600 | Sept. 6| 79° |163,200 | Oct. 25\), 48°° || 44500 “~27)| 73° |494,400 486,872 | 195,834 | 11,650 It will be noted that all the pulses with one exception lie above 70°, averaging in fact 78.25°, indicating an optimum temperature 166 near the summer maximum. The location of the pulses with respect to those of the chlorophyll-bearing organisms (Pl. II.) shows in the main the same relation that has been observed in other ploiman rotifers. In 1895, three angularis pulses lie in the period common to both, one of these coinciding in location and two following at the next collection. In 1896,two coincide and five follow at the next collection or shortly thereafter. In 1897, four follow at an interval of a week or a fortnight, and one is located where data are incom- plete. In 1898, three coincide and three follow at a short interval, and one (June 7), a minor and ill-defined pulse, appears to lie on the rise of the pulse of the chlorophyll-bearing organisms. In the main the dependence of these rotifer pulses upon the recurrent periods of increase in these primal links in the food cycle is suggested by this coincidence or sequence. The pulses of Brachtonus angularis co- incide in the main with those of the totals of ploiman rotifers (Majo la). There is no vernal pulse in the species at the time of the April— May volumetric maximum, and no large autumnal pulse. The pulses in August-September, at the close of our period of maximum heat, average much greater than those of other months, and still further indicate the relation of this species to the higher temperatures. The eggs are carried by the female attached to the posterior end of the lorica. Usually but a single summer egg is carried at one time, but often two, three, and even four, have been seen during the height of the period of rapid reproduction. -The relation of the number of eggs to the pulses is obscured in this species to some extent by the fact that the eggs are similar to those of other Brachto- nus and when detached cannot be identified with certainty. Records are therefore based upon attached eggs only. The number of these depends to some extent on the detachment im the processcaven collection, killing, and subsequent handling. In a few cases de- tached male or winter eggs could be identified with some degree of probability by the constitution of the rotiferan plankton. An examination of the records of eggs (Table I.) will, however, suffice to indicate the prevalence of rapid reproduction during the rise of the pulses and the decline in the process during the fall of the pulse. Males, male eggs, and winter eggs were recorded in a number of instances at the culmination or during the decline of a pulse. For example, in 1898, they followed the pulses of August 16, September 167 6, and especially that of September 27, when they were found con- tinuously for a month. : The separate records of the type and the variety (Table I.) contain in their seasonal distribution one point of special interest; namely, the appearance of the variety ajter the type has been present for some time. An examination of the records in the several years reveals the fact that var. bidens is practically confined so far as large numbers are concerned to the months of July-September. This appears in 1898 (Table I.) and is equally evident in 1896 and 1897, but is less noticeable in 1895. The first large pulse is passed in each year before var. bidens takes any appreciable part in the genesis of the pulses. Even the second large pulse is not extensively con- tributed to by the variety in some instances. On the other hand, the later pulses in 1895 and 1897 were mainly of the variety. There is thus in this species some evidence of a tendency on the part of the variety marked by the development of a patr of posterior spines to appear in the latter part of the period of seasonal occurrence. The variety bidens in our records includes individuals with well- developed spines (8. caudatus Barrois and v. Daday), but they are not to my mind worthy even of varietal distinction, since they intergrade so completely with var. bidens and are merely well-de- veloped examples of this variety, and I see no reason for giving the variety two names. Wesenberg-Lund (’00) has expressed the opinion that the elonga- tion of structural processes which he has noted in summer planktonts is an adaptation on their part to the changes in the buoyancy of the water dependent upon changes in its specific gravity and, as shown by Ostwald (03 and’03a), in its molecular friction caused by seasonal fluctuations in temperature. It would seem that this tendency on the part of the spinous form of Brachionus angularts to appear in greater proportions in late summer at the period of maximum heat in our waters might be an illustration of Lund’s thesis and Ostwald’s theoretical considerations. The changes in temperature during the occurrence of the species are, however, not very great, though our incomplete records suggest (Pt. I., Table III. and Pl. X.—XI1.) that August temperatures are higher on an average than those of July. The averages for June, July, and August are 77.75°, 81.03°, and 81.49°. In 1897, the dominance of the spinous type extends well into September, but it accompanies a period of summer hea Coes 168 Pl. XI.) prolonged for a fortnight into September, with river water at or above 80°. In 1898, it falls away in numbers more rapidly than the spineless form (Table I.) as temperatures fall in October, though this tendency is less marked in previous years. Brachionus angularis, as above stated, seems to be -rare in the plankton of our more northerly and cooler American waters. It is also conspicuously absent from plankton of Swiss waters, as reported by Weber (98) and Burckhardt (00 and ’00a), and from German lakes examined by Apstein (96), Zacharias (’98), and Seligo (’00), and from Finland waters examined by Stenroos (98). It was, however, found by Wesenberg-Lund (798) in Danish waters, and in the Udy River, in Russia, by Skorikow (’97), whose statistical records show it to be the most abundant Brachionus in that stream, and outnumbered among the rotifers only by Syncheta stylata and Polvarthra. Schorler (00) finds it in the Elbe from April to July and most abundantly in June. Lauterborn (798) reports it as perennial in the Rhine and polycyclic, with winter eggs in April, June, August, October, and November. This distribution is much like that in the Illinois River, and will probably be found in tem- perate waters wherever the seasonal cycle is thoroughly examined. Brachionus bakert Ehrbg.—Average number of females, including all varieties, 594; eggs,420. The following table, giving the average of each of the varieties in the several years, will serve to indicate their relative abundance, the totals showing the relative abundance of the bakert group in each year and of each variety in the total of all the collections. Though the species is greatly diversified by variation the number of individuals is much less than that of many other plankton rotifers in which variation is much less apparent. It will be noted that the species was apparently more abundant in the earlier years. This is only in part the result of the distribu- tion of the collections, as is shown by the fact that the numbers taken were much larger. Thus in 1898 the largest record is 7,600; in 1897 there are three occurrences in excess of this; in 1896, two; in 1895, three; and in 1894, four. The largest occurrence, 122,958, was on June 30, 1894. The largest numbers by far were recorded in 1894, a year of low water in spring. The hydrographic conditions of the following year were somewhat similar, but the development of B. bakert was much reduced, at least at the time of the collections. LCG Ve OCT Cry Tso'T O£9 BLOT $330 TeIOL 628 PE IZZL OISSZ ZUTIL ZSPl tb OST 6S Ge iecr en lope ho coh c 99) 1206 = tr Ist 0 LS6‘Tt |6@Z2 (919 |90T [z6z OL SOP % (992 SOL Tip Zs OF LLO‘LZ [691 ‘90F0 ‘OTIPL8‘Tlezs‘¢] ¢€9 sso] 6 s3s0| 6 | ssso sjenp “IATpUr | snjno4aqny mMmMayjau 1e10L, OLS 69 6L LSC 691 5 od4y 24ayng SNS a pal Veh aa| LL2°S| 196 $\989°TT coe | £6T 99T 1210L } = = = = ST Cele eel leanT “$6 (06 zo | «IP ras 8681 98 BCG OS | COL 1) Ove MCvOmtalebve leven oe LOST GSz1 soe | 9 OFT | 2ee> \2rr 0 ST oF 9681 Z OG | OFF lalOe a 9em 1008 0) 0) Te S6st 6T 6T | 4£6°%| 9S9°F| 18° P/ELZ°6 | O 0 Or POST $330 ro) $3839 ro $330 } Re 5 snurds12a4q SnUDUaYAs Seoaaite nj S$NSIQO ete Iva SOTJOLIV A uorpoT]oD ied roquiny os8eI0Ay TaNUAVA SNNOIHOVAG 169 4 170 The reducing effect of the recurrent floods of 1896 may be traced in the smaller numbers recorded in this year; and the larger num- bers of 1897 may be referred to the more stable conditions then prevailing. The very small numbers of 1898 may also be due to disturbed hydrographic conditions of that year. The number is much smaller than in 1896, when the hydrograph was even more disturbed, but in this latter* year there was more run-off of impounded backwaters during the occurrence of B. bakert,and this would tend to favor their appearance in channel waters. The occurrences and numbers of this species (as a whole) are everywhere somewhat irregular, so that pulses of occurrence are somewhat ill defined. Several such pulses are indicated in 1898, and others recur in the records of previous years. As suggested by the data of 1898 (Table I.), the several varieties share in these pulses. The evidence upon this point is much more striking in other years, when numbers are larger. For example, in the following table note the pulse of 26,800 on August 23, 1897. i) x < = s 4 Date ‘3 < ss "3 aS Total 4 3 = a s = S S S 8 S 3 9 S xy io) S WwW INOS Oss peace O 0) Q O O 200 200 1 eo eR RAIN, O 1,200 200 600 2,000 5,200 7,400 DS ieee O 7,800 1,800 3,400 2200) 11,600 | 26,800 Mere 2 0) 200 400 200 O 1,000 1,800 In their location these pulses exhibit as a rule the same relation of coincidence or sequence to the pulses of chlorophyll-bearing organ- isms noted in some other species, and they frequently coincide with those of other Plowma, but not always. This is perhaps the most variable of the rotifers of the plankton. At least its variations affect the fixed processes of the lorica and are thus quickly and easily appreciated. The species, in common with 171 B. pala, B. angularis, and probably B. urceolaris, has a variety—in fact, several varieties—with two posterior spines which are usually symmetrically placed but not always symmetrically developed. The form without posterior spines (var. clumorbicularis Skorikow) inter- grades with these, and a series might be formed with complete intergradations linking this in turn with var. rhenanus Lauterborn, in which the spines are but slightly and often unequally developed. From this we pass, by a slight elongation of the posterior spines, to var. brevispinus Ehrbg., thence to the type in which the spines as figured by Rousselet (97) are directed posteriorly with but slight curvature. From this we may pass toward variants in which the symmetry is preserved, but the spines are much elongated and curved outwardly. The anterior spines in such individuals are also more elongated and exhibit a similar outward curvature (var. melhemt Barrois and v. Daday). Extreme types of this curvature sometimes occur (B. falcatus Zach.). In another direction we find the bilateral symmetry of the processes, both anterior and posterior, to some extent lost as a result of differences in the curvature of the spines (var. tuberculus Turner). There are also differences in the surface markings of the lorica which have been utilized as specific distinctions. Kertész (’94) describes as B. granulatus a species with a minutely pustulate surface, and Turner’s B. tuberculus takes its name from this same feature. It seems questionable, however, if these surface markings are even of varietal value. Individuals without spines, in which the transverse diameter is relatively large (var. obesus Barrois and v. Daday), are also found. In assorting the individuals belonging to this variable group I have arranged them under the following heads: bakeri O. F. Mull, bidentata Anderson (non bidentatus Kertész), brevispinus Ehrbg., cluniorbicularis Skor., melhemi Barrois and v. Daday, obesus Barrois and v. Daday, rhenanus Lauterborn, and tuberculus Turner. The number might have been increased. The individuals referred to var. melhemi include many if not all of the long-spined specimens such as Rousselet (’97) has referred to the type, the latter designa- tion having been given to individuals intermediate between this and brevispinus. The variety tuberculus includes the asymmetrical individuals, regardless of the surface markings. I will now briefly compare the seasonal distribution of these varieties and note any peculiarities which mark them individually :— 172 Brachionus bakert O. F. Miull., type form.—Average number, 2. As shown in table on p. 193 (MS.), this form is much more abundant in previous years though it 1s relatively rare, ranking sixth in the list of seven forms recognized. The most of the records fall prior to the middle of August, and it seems to be an early rather than a late summer form. Brachionus bakert var. obesus Barrois and v. Daday.—Average number of females, 41; of eggs, 62. The proportion of ege-bearing to non-egg-bearing females—2 to 3 in all records—is larger than in any other variety. It seems probable that the lateral expansion which marks this variety may be only the result of rapid reproduc- tion. In common with most of the other varieties this one occurs at the time of the pulses, but it is last in the list of seven, and the numbers are too small to trace its seasonal preferences with cer- tainty. Brachtonus bakert var. bidentatus Anderson (non Kertész).— Found once—August 5, 1895, at 78°. Brachionus bakert var. cluniorbicularis Skor.—Average number of females, 90; of eggs, 95. This also was more abundant in all previous years. This variety is, next to tuberculus, the most abundant of the varieties in our plankton. The two stand at opposite extremes of the series of varieties, the former being least modified, and the latter most, especially in the direction of asym- metry. It includes about one third of all the individuals of the species. The ratio in the grand total of females to eggs carried— 11,708 to 5,976—is somewhat less than the average in the entire species. This variety is distributed throughout the whole seasonal range of the species with no marked predominance in any particular part of it. Itis wholly absent in the early summer of 1897, but very abundant in late summer of that year, though not in other years. The autumn of 1897 was one of long-continued high temperatures (Pt. I., Pl. XI.), and under those conditions this variety constituted two thirds of the individuals belonging to the species. If we add to it the representatives of rhenanus, obesus, and brevispinus we have a total of 15,400. individuals with no posterior spines, or with spines but slightly developed, in contrast with only 2,200 with such well- developed spines referred to varieties melhemi and tuberculus. The conditions of temperature were those in which according to the 173 hypothesis of Wesenberg-Lund (’00) we should expect a predomi- nance of the long-spined forms. Brachionus bakert var. rhenanus Laut.—Average number of females, 118; of eggs, 138; but more abundant in previous years. This is the third in numbers on the list of seven varieties, being surpassed only by clumorbicularts and tuberculus. It includes about one sixth of the individuals referred to this species. It is found throughout the whole range of the seasonal distribution of the species and exhibits the same peculiarities noted in cluniorbicularts, to which it is very closely related. The proportion of females to eggs noted in this variety is very large; 5,284 to 5;485 in the grand total. Brachionus bakert var. brevispinus Ehrbg.—Average number of females, 795; of eggs, 390; but somewhat more abundant in previ- ous years. It was found throughout the whole seasonal range of the species, but not quite so abundantly in the latter as in the earlier half of the summer, resembling in this particular the type. The number of eggs carried in this species is in relation to the number of females less than usual—3,906 to 795. Brachionus bakert var. melhemt Barrois and v. Daday.—Average number of females, 49; of eggs, 49. More abundant in previous years, especially in 1894, when it constituted over a fifth of the individuals (25,764) in the largest pulse recorded for the species as a whole—122,958 on July 30. Inthe aggregate in all years it includes only about a ninth of the individuals referred to the species. - This form was originally described from Syria, but it is found in great perfection in our plankton, even in the extreme type described by Zacharias (98b) as B. falcatus. It occurs throughout the whole seasonal range of the species, its distribution being somewhat similar to that of tuberculus. I do not find any constant tendency limiting its occurrence to any part of the seasonal range. Brachionus bakeri var. tuberculus Turner.—Average number of females, 155; of eggs, 42; but very much more abundant in previous | years, especially in 1894, when it constituted almost half (55,332) of _ the largest pulse of the species (122,958), This, the most divergent of all the varieties, constitutes over a third of all the individuals referred to the species. It occurs throughout the whole seasonal range of the species, though the larger numbers were found in 1894-97 in the earlier part or middle of the summer. I find nothing 174 in a comparison of the seasonal distribution of these more decidedly spinous varieties of B. bakert with that of the smoother forms, such as cluniorbicularis, which indicates any correlation with temperature conditions of a nature to support Wesenberg-Lund’s suggestion that the elongation of the processes of plankton organisms arises in response to the lessened buoyancy of the water during higher tem- peratures. Forms with and without such processes are found among the varieties of this species, and both occur indiscriminately through- out the whole range of seasonal occurrence, and, so far as I can see, the statistical data of thetr distribution with respect to temperature afford no evidence of a correlation of spinosity and high tempera- tures in this species. Other factors doubtless enter into this problem and obscure this response if it exists. B. bakert is everywhere widely distributed in fresh water. Its occurrence in the plankton of open waters has not, however, been a matter of frequent note. In fact there is some reason to think that it 1s largely confined to shallow warm waters where vegetation 1s close at hand, or where at least the flagellates and smaller alge abound, as they do in water fertilized by decaying vegetation or other organic matter. There is, it seems, no reason for regarding this species as merely adventitious in our plankton. It bears all the characteristics of a true limnetic organism in our environment. Its presence in the plankton is not due to floods or other disturbances which might carry it from a littoral region into the open water. It exhibits characteristic pulses, and is found everywhere in summer in company with typical planktonts in open water. Zacharias (’98) records it in some German ponds and streams, and Weber (98) in Swiss marshes in the warmer months. Stenroos (98) also finds it in the summer plankton of littoral and open waters in the shallow Nurmijarvi Lake in Finland. Jennings (’00) reports it as one of the commonest rotifers in East Harbor, Lake Erie, and in the swamps on the islands. In land-locked pools short-spined varieties were found, and in swamps the long-spined. Speaking of this difference, Jennings says ‘“‘ Possibly the different form found in these pools is due to the greater concentration of various salts in this water or to some kindred factor.” In our own region both varieties occur at the same time in the same environments, channel and backwaters alike, and such factors as Jennings suggests to explain the appearance of the varieties cannot well be operative here in 1S channel waters. Schorler (’00) reports the species as sporadic in the Elbe, and Skorikow (’97) finds both B. bakeri and its variety brevispinus sparingly in the Udy in summer months. This species in common with other brachionide was infested by Bimerium hyalinum Przesm., and occasionally by a filamentous fungus-like growth. Empty loricee were wont to appear with the culmination of a pulse and subsequently. No males were identified as belonging to this species, and attached male eggs were recorded only late in September, 1897, at the close of an unusual pulse. They were found on var. cluniorbicularts and rhenanus. Females with winter eggs were not at any time recorded for this species. . It may be that some of the free winter eggs referred to the genus Brachionus (Table I.) belong to this species. The recurrent pulses are similar to those of known polycyclic species, and we may infer the probability of such a phenomenon in B. bakert, though conclusive proof of its occurrence is not found in the statistical records. Brachionus budapestinensis v. Daday.—Average number of females, 4,211; of eggs (carried), 740. This is one of the most sharply defined species of Brachtonus and a typical planktont of open waters. It has, moreover, a sharply limited seasonal distribu- tion in which it is apparently polycyclic. The appended table gives the dates and temperatures of appearance and disappearance and the pulses in the several years. In the main, the period of occurrence is practically from the end of June till the early part of October and above 60°. A record in May, 1896, and an isolated one in December of the same year, indicate an extension of this period, but such occurrences are rare and irregular and the numbers small. This abrupt decline in 1898 as temperatures pass 60° (Pl. XII., Pt. I., and Table I.) is paralleled in previous years. The normal seasonal routine seems to be as follows: The species reappears in the plankton in May-June at 70°, rising slowly to its first pulse (average, 26,104) in July, with a larger pulse (average, 184,453) in the following month during the maximum heat, and a much smaller one (average, 10,044) in Sep- tember, followed immediately by an abrupt decline. The average temperature of the larger pulses lies close to the season’s maximum, while the latest pulse at the lower temperature (72.2°) averages but 10,044. These data all indicate that this is a midsummer planktont, with its optimum temperature near the summer’s maximum. The "O6O8T ‘¢ “99d SuryqTUIO} ee. 19 uO Olen CL ESP‘TST | o8 82 FOL OGalo04 18 BG EL h rec eae ee ae “OSCIOAY peor lciee 12On| OOS pr eee, ne 1029S | 000" 0 Sh OT SIM OOO Se eee AG ASU = eh org erate St as os 868T HOO SG) Oa =| 2 meles) BGOnalee pas On | O08 +. AG lace MOO MINOUOL OC O Ei Ge cove ROOG heal ear ee OC =A IN| Or. Pe Nit eee meinen: L681 goon leo. eee (LOOTED Soc i Opmiaes Oe (Te eal SoG elsOe J6SGu 000" 7 SOL Nees “ease | 1000). tis AC, WS MO OMe ol NE Bie I RGR Os *968T 0 ™~ sUSisee: Orta Oe ote cee |b ens : Roel re Ios ae Oey o8Z | 02 3deS | 499‘8r oG8 | be aby | O18 ¢ AO 3 “0M SO Gh ua ES eee S68I 6G lakh Adess oor Be |) jz eS sees 76 Se GG SEL oy a] re Shed PF ee F681 ‘duey,| eq “ON [dwey| eq ‘ON ‘dwoy| oVq ‘ON |dwey| seq |;dwoer| eq As ten was Ivo PlOIIY ISP] sos[ndg psloos9y ISAT “SISNANILSAd VON SNNOIHOVAG AO SasTnd 177 relation of hydrographic conditions to the relative development of pulses in different years is seen on a comparison of the record for 1896 and 1897, the former (Pt. I., Pl. X.) being a year of recurrent Moods and the latter (Pt. I., Pl. XI.) one of stable conditions through the greater part of the seasonal distribution of the species in question. The average numbers in these two years were 3,105 and 31,306, respectively, and the average amplitude of the pulses 18,250 and 97,200, showing, respectively, a ten- or five-fold increase in the latter year. The extension of the heated term into September in 1897, is reflected in the large September pulse (552,000) and in the extension of the period of occurrence into October. The locations-of the pulses of Brachionus budapestinensts in 1898 correspond with those of the Plowma in general.. They likewise coincide with or follow those of the chlorophyll-bearing organisms (cf. Pl. I. and II]. with III. and IV. and Table I.). Similar relations are apparent in 1896 and 1897 but are less evident in prior years. They suggest an interrelationship of the pulses in this species with the fluctuations in the food supply. Males, male eggs, and winter eggs were not recorded, but the recurrent pulses in this species are so similar to those in other rotifers in which the evidence of the occurrence of sexual reproduction at the culmination of each pulse has been found, that the inference may be made that this species likewise is polycyclic in our waters. Females carrying one or two summer eggs have been found in greatest abundance during the rise of the pulse, and only in small numbers, if at all, during its decline. This species is subject to some variation in the development of surface ornamentation, in the ratio of width and length, and in the curvature of the median spines. It is usually somewhat more slender than figured originally by v. Daday (85) or even by Hempel (96), who described a form somewhat more slender than that figured by v. Daday, as B. punctatus. Shortly afterwards Skorikow (’96) described the same species as B. lineatus from Russian waters. The name given by v. Daday has priority, and as neither the Russian nor the American forms are to my mind well enough set off to merit even varietal distinction, I have used the name given by v. Daday, and have included under it both wide and narrow forms and those with incurved or outcurved median spines. The fact that their common record of seasonal distribution forms a seasonal curve of 178 typical character is corroborative of the view, though not conclusive, that we are dealing with a single species and not with several. This species has not been widely reported in the fresh-water plankton. It is evidently a planktont of warmer waters, and for that reason may have escaped notice, since the cooler waters have been the more thoroughly explored. Thus it was not found by Weber (’98) in Swiss waters in his thorough explorations about Geneva, nor by Jennings ('94, ’96, ’00) in the Great Lakes or inland waters of Michigan. It has, however, been recorded by Skorikow (97) in the plankton of the Udy River, in Russia, where it was exceeded in number by only two species of its genus, B. pala and B. angularts, ranking tenth in numbers among all the rotifers. His data of frequency from July to October suggest several recurrent pulses. It has likewise been found by Lauterborn (’98) in the plankton of the Rhine, where he classes it with the stenothermal planktonts. Zacharias (98) finds it in ponds near Leipzig, and it was originally described by v. Daday (’85) from Hungarian waters, and again noted there by Kertész (94). Fuller exploration of the summer plankton in warmer regions will doubtless ae the record of its range. Brachionus militaris Ehrbg.—Average Anan be of females, 147; of eggs (carried), 98. In previous years the species was much more lena eins the averages in 1897 being 1,412 females and 523 eggs, and in 1896, 1,288 females and 576 eggs. This greater development in years prior to 1898 is evident in many of the Brachiomde. The following table gives the dates of first and last records in each season, and the location, temperature, and amplitude of the pulses in the several years. This is evidently a summer planktont with well-defined limits. These limits appear much less evident in 1898 (Table I.) than in prior years. In 1896 and 1897, for example, the species is almost continuously present in the plankton from the time of its first appearance until the last record for the season. All of the records save two lie above 70°, and the average temperatures at which the pulses occur are all at or above 80°. Its optimum thus lies near the summer maximum. The lower limits are not definitely established owing to insufficient collections in periods of rise and decline, but they seem to lie near 70°, with small numbers lingering to 60°. of4 | £2 3deg | ooz‘e | ozs | of ‘8ny | ——— | —— | ——— ] 02] 84 | ch AIDE) cre | ve Key | 8681 009 | 9 eo) ‘ ‘ seat ne pete Rr obe | be 2des | G00 7 || 08. | Te any! o0sF. | sie Ob Sny| 000°rZ | 084 | Pt AME] og2 |et 4mf|------- L68T OOO) He ey Se ay 08S | Of 3deg | ——— | —— | —_— | o9z'z | ozg | st -3ny| ooz‘¢ CUR aC AT ace lst ayn ee eee 968T DPE eH Fle al elegs Se Mie gee: on ete emer A 064 | 02 3deg | OOF‘T cS leh 1GeSh ieee. 7, 084 | Tt “sny | ——— | —— | ——_— | -.9¢ | ez 4mf|::-- S681 & o8L | b ‘3deg | szz‘b | 84 | F 3dag : OUD e Goal ech ee Aru aeijen ie Wott (igiere sci tenes FO8T ‘duy,| seq | on |dwey ayeq ‘ON =| dwoy) aeq ‘ON |dwey| ayeq |duey| eq’ : Ivo P1ODOY, 4SV’T sos[ng : PIOIOA SIT =, x p ee ee eee as i ; ; ' ‘SIUVIITIN SANOIHOVYG 40 SasTng 180 This species has never developed large pulses in the channel waters of the Illinois. Hempel’s statement (99) that it is “the most abundant species of the genus’ can apply only to certain collections in vegetation-rich backwaters, for in the river it is sur- passed in the totals of occurrences in the statistical records by eight other forms of /rachionus, namely, variabilis, pala, amphiceros, dorcas, rubens, budapestinensts, cluntorbicularts, and tuberculus. J found it in very great abundance in the July—August plankton of Crystal Lake, a shallow warm pond rich in vegetation,formed by damming a small creek tributary to the Wabash system, near Urbana, Ill. From the relatively small numbers, the slight ampli- tude of the pulses, and their somewhat irregular development I am inclined to think that the centers of distribution of this species are not in the open water of the river and its backwaters, but more in the vegetation of warm, shallow regions such as the margins of our bottom-land lakes. It is thus to some extent adventitious in our plankton. The pulses of this species are relatively so small that they do not contribute an appreciable amount to the total ploiman pulses, nor do more than 50 per cent. of their number coincide with such general pulses, though they are sometimes found during their rise. The greater part of them coincide with the pulses of chlorophyll-bearing organisms (Pl. I. and II.), suggesting a food relationship. This species is one of the best-defined in the genus, though in the character of its asymmetry it varies toward B. bakert var. tuberculus Turner. It exhibits some variation in the degree of asymmetry, in the curvature of the spines, and in the surface markings. The indi- cations of pulses suggest a polycyclic habit, but no evidence in the way of males, male eggs, or winter eggs was recorded which will substantiate the inference. A female carrying a winter egg was found Sept. 21, 1897, at the close of the period of occurrence. Fe- males with one, two, or three summer eggs were found throughout the summer and in somewhat larger numbers -during the rise of the pulses. Brachionus mollis Hempel.—Average number of females, 137; of eggs, 10. More abundant in previous years, the average in 1897 being 1,092 and 277, and in 1896, 428 and 56. This likewise is a summer planktont. The earliest record of its appearance in the plankton is June 17, 1896, at 76°; and the latest, 181 October 17, 1894, at 58°. With but two exceptions the species was taken only above 70°, and the period of most continuous occurrence and largest numbers is near the summer maximum of 80°. The optimum is thus near the summer maximum. This species was never taken in the plankton in large numbers, the greatest being on Sept. 14, 1897 (20,000), at 84°. On account of the small numbers and somewhat irregular occurrences the phenomenon of recurrent pulses is here less apparent than it isin more abundant species. The appended table records the best-defined ones. These pulses share in the general ploiman pulses in only about 50 per cent. of the cases, and the most of them coincide with or follow saintly after the pulses of chlorophyll-bearing organisms. PuLsES OF BRACHIONUS MOLLIS Year Date Temp. No. Date Temp No. Wa95.;..| July 6 81° 742 Sept. 5 Us? 954 1896....| July 18 79° 1.200- | Aub. +211 79° 8,400 weo7....| July 30 So" 11,600 | Sept. 7 80° 20,000 a598....| Aug. 23 Sil 800 Septe 2/7, 13° 4,800 So far as I am aware this species has not been found in other waters than the Illinois River and its adjacent backwaters. Hempel (99) reports it as most abundant in the marshy environment of Flag Lake. Brachionus pala Ehrbg.—Average number, including all varie- » ties: females, 19,969; eggs, 25,974. The following table gives the " average number, in the several years, of the varieties here included, and it will serve to show their relative frequency. This is the most abundant species of the genus in our waters, the grand total of all occurrences exceeding 9,000,000. As a whole the Species was much more abundant in the stable year 1897 (180,998), and less abundant, all things considered, in the disturbed conditions of 1896 (36,665). As a whole the type form pala is less abundant than amphiceros. It forms but 28 per cent. of the total, as compared With 68 per cent. included in the latter variety. Dorcas forms less COT LLET 198‘ F87 ce 669-c | 807 ¢ TO} 2 eEHGA GS (CSCS) Pole G0. LSairOlD.o7 99T 2S EON, 886° STZ 196‘ 61 G g¢ TL OLT ONG TAO LY | GORE | SEO" cS 868T 607 ‘89 866‘ O8T OF 90T 0 Le G29 SE | 967 9ST VS‘ ZE | SLY‘ HZ o¢ Lo8t 867 LZ gs9‘9oe 1Z rge'z | 60¢'Z 9129 pL Ost 's Sy PT S79 ‘77 oF 968T 826‘ FE 8ce ST Gill 90T SO! OSGI (QO EE | COSI WN GG 66 IAGO) ke T¢ S68T OTS 16 1 0 0 0 Y ce 6ST SLT OS2 1 OT F681 soy 5 sso ro) ssa o) ss3q $339 S[enprArputr SUOT}OI]JOO neue [®10OL [e10L JO "ON A snsoutds spo4.0p sosaory dup ppd “NOILOATIO[) add UFdNOAN AOVAGAVY “SGILGIYVA GNV VIVd SONOIHOVAG 182 183 than 2 per cent; and the form spznosus, less than 1 per cent. The proportions formed by the several varieties fluctuate from year to year and from season to season,—indeed, from collection to collec- tion (Table I.). Thus in the first three years pala exceeded am- phiceros, while in the last two these conditions were reversed; and in 1896 the form spimosus contributes 6.5 per cent. of the individuals. The predominance of the pala-amphiceros group is, however, preserved throughout all of the years. The species as a whole is found throughout the entire seasonal range of temperatures but with very great fluctuations in numbers. Speaking generally, there are vernal and autumnal pulses separated by a midwinter minimum which is well sustained, developments in excess of 5,000 per m* being very rare in this season. There is also a midsummer minimum more or less diversified by pulses of some magnitude. This sequence was not fully realized in any single year of our records, but this may be due in part to insufficient collections at times of the major pulses. Thus in 1894 only a small autumnal pulse (13,650) was detected. In 1895, there was a small vernal pulse (67,338), and a belated autumnal pulse (320,915) lasting a full month in November—December. In 1896, there was a very abrupt vernal pulse rising from 53,618 on April 17 to 1,012,350 on April 24, while in the fortnightly fall collections the only pulse detected was one of 14,000. In 1897, the monthly collections of the spring seem to have missed all considerable developments, the largest recorded being only 16,000. On August 31 and October 12 of that year, however, there were pulses of 1,398,000 and 1,605,600. In 1898 there was a well-developed vernal pulse of 451,200 and a small autumnal one of 83,200. The species is not, however, dicyclic, for both the winter and summer interims are marked by occasional recurrent pulses of smaller proportions. The table on the next page shows the loca- tions and temperatures of the culminations of these pulses. From this table it is evident that a wide range of optimum tem- peratures is possible. Nevertheless, 23 of the 31 pulses occur above 50°, and 21 of them above 60°. In 1898 only 3 per cent. of the individuals are found below 57°, and with the exception of 1895 approximately these conditions will be found in the other years. Brachionus pala is thus a perennial planktont, but as a rule it reaches its largest developments only above 60° in our channel waters. 184 Putses oF BRACHIONUS PALA AND VARIETIES. Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 = = = S—S== = a =a ——— ———— 1895 = = —— ———— a = —=— 1896 Jan. 1 306 8,268 Jan. 25 33° 5,928 ———_— —_ | ~—— 1897 — —= —— === =— 1898 ——_ — ——_— —— == Se Mar. 22 Syl) 1,720 Year Date Temp. No. ‘Date Temp. No. Date Temp. No. 1894 == —= ———= ———- =—= SS — ——— 1895 Apr. 29 64° 67,338 ee —= ——= 1896 Apr. 24 TBI Ml OUAW 0) May 25 eo 4,400 1897 May 25 66° 16,000 Sas == 1898 May 3 60° 451,200 | June 14 83° 1,000 Year Date | Temp. | No. Date Temp. No. Date Temp. No. 1894 July 30 82° 1,908 Sept. 4 78° 13,650 1895 July 6 81° 3,710 Aug. 21 81° 47,480 | Sept. 20 79° 2,223 1896 July 23 Hise 12,600 Aug. 3 80° 39,200 | Sept. 30 58° 14,000 > pamegelS 81° 12,800 1897 July 30 84° 11,200 Aug. 31 80° |1,398,000 = ee 1898 July 19 g4° 6,400 | Aug. 16 aie 38,400 | Sept. 27 73° | 83,200 ] ; Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 | pee i ea 1895 Nov. 27 goo 320,915 SS = 1896 Dec. 29 30m 14,120 1897 Oct l2 65° |1,605,600 Nov. 23 43° 1,160 == 1898 Octerz5 49° 8,500 Nov. 15 41° - 1,100 Dec. 15 a2e 3,100 185 The pulses recorded in the table will be found to coincide (Table I.) with those of other species of the genus, and in the main with those of the total Plowma, thus indicating that this species responds, along with other rotifers, to some common factor of their environ- ment. The relation of these pulses to those of the chlorophyll- bearing organisms (PI. I. and II.) is also striking. Of the 30 pulses recorded in the table, 6 fall outside of the period included in Plates T.and II. Of the remaining 24 there are 17 whose culminations in the main coincide with those of the organisms upon which they feed, and 5 of the 6 remaining follow shortly thereafter, usually at the next collection, at an interval of a week or thereabouts. In one case only is there a delay of a fortnight after all of the plant pulses. The large pulses of August-October, 1897, were judged by the Chlorophycee only, as these overtop the other plants so greatly. The pulse of August 31 occurs a week before the culmination of the Chlorophycee is reached, but in the presence of abundant food. The dependence of these pulses of Brachionus pala upon the food supply is plainly suggested by their time relations with the pulses in the plant life of the plankton. Further reason for concluding that the species 1s polycyclic is found in the evidences of sexual reproduction, which will be noted in connection with the discussion of the varieties. In this connec- tion it will suffice to say that there is some evidence that the pulses are preceded by rapid parthenogenetic reproduction, and accom- panied or followed by the appearance of male eggs, males, and winter eggs. The eggs of Brachionus pala are detached from the parent in such a large proportion of the cases in preserved material that the tracing of the reproductive cycle by means of attached eggs is ren- dered difficult if not impossible. Furthermore, eggs resembling the winter eggs of this species,and provisionally referred to it in our records, are to be found in the plankton at nearly all seasons of the year, and it is obviously impossible to determine the time at which they were produced. It seems probable that all of the varieties pass through recurrent cycles, and that none of them is a temporary phase of the cycle. Outbreaks of parasitic diseases in this species are very common. They almost always attend the larger pulses, but isolated individuals infested by some of these pests are not infrequent, especially during 186. the summer months. Thus in the vernal pulse of pala (type only) reaching 716,982 on April 24, 1896, 19,056 individuals were para- sitized by Bimerium hyalinum Przesm., or by something very similar to it, and 30,966 were infested by a fungus-like growth. This is about 7 per cent. of the total individuals. Similar though less pronounced outbreaks have attended other vernal and autumnal pulses. Species of Colacium are sometimes found attached to the loricee of this species. Brachionus pala is exceedingly variable, especially in the matter of the development of the posterior spines. Forms without the spines (pala type) intergrade, by only slight gradations, into those with fully developed spines (var. ampliceros). The angle which these spines make with the lorica is also a matter of great variation, in preserved material at least. Individuals with the spines at right angles to the antero-posterior axis are occasionally seen. The species also varies in the matter of the dorsal-ventral curvature of the antero-median spines (var. dorcas). Individuals with such curved antlers are sometimes provided with posterior spines (var. dorcas form spinosus). I have followed Weber (98) in placing B. amphiceros Ehrbg., B. dorcas Gosse, and its form spinosus Wierz. as varieties of B. pala. They do not, however, all stand upon an equal footing. B.amphiceros grades imperceptibly into B. pala, and has the same seasonal distribution. 6. dorcas and its form spinosus intergrade with each other as do pala and amphiceros, and they also exhibit some intergradations with B. pala; but they are winter varieties, or at least belong to the colder season, as will appear later. Their differentiation in this respect is thus more striking than that of B. amphiceros, and makes it probable that we have in dorcas a seasonal variety of B. pala. Zacharias ('98) has reduced B. pala to a variety of B. ampliceros because in his opinion the latter is the more widely distributed form in certain pond waters which he examined. This is a criterion which presupposes a wide knowledge of distribution and numbers, and, furthermore, a basis which can not fail to add to the confusion already existing in this genus, since it is hardly to be hoped that it will lead to the same conclusion in the hands of different investigators in different regions, or even in different seasons and years in the same region. As an illustration of the difficulties which might arise I may cite the yearly averages of amphiceros and pala in the table on page 182. In three — 187 years the latter is more abundant, and in two, the former. The relative abundance of these forms in the river at a given point of collection is an epitome of their distribution in a wide area of channel and backwaters. An application of the principle advanced by Zacharias would in this instance lead to constant change. The retention of pala (Ehrbg., 1830) as the type and amphiceros (Ehrbg., 1838) as the variety is in keeping with priority in nomenclature and with the principle of regarding the more highly differentiated or divergent form as the variety. Variety ampliceros occupies thus the same relation to the type that bzdens does to its type angularis. Both are illustrations of the tendency common to all species of _ Brachionus to develop posteriorly directed spines. ' I shall proceed to discuss the salient points in the seasonal dis- tribution and statistics of the several varieties :— Brachionus pala Ehrbg., type.—Average number of individuals, 2,693; of eggs, 20,809, including all free eggs referable to the species in the broader sense. In the present connection I shall call attention only to the fact that the type form, without the posterior spines, is less abundant during the midsummer interval than the spinous variety ampliceros. This appears in Table I., and is to be found in the records of years prior to 1898. A fuller comparison of the records of the two forms will be made in the discussion of amphiceros. I shall not discuss the recurrent pulses of this form or of amphiceros, since as they dominate those of the species as a whole it would lead to considerable repetition. The pulses of pala in the main (Table I.) coincide in location with those of the species as a whole, and the direction of movement of the seasonal curve of distribution is quite similar, save in the fact that the amplitude of the pulses is less, and that the differences in seasonal distribution between pala and ampluceros modify the curve of each. The decisive evidence of sexual reproduction in the species in the form of attached male and winter eggs is found repeatedly at times of the major pulses. In some instances they appear during the rise oi the pulse. The autumnal pulse of 1895 will serve as an illustra- tion of the character of these statistical data. (See following page.) This pulse is sustained much longer than usual, but it serves to show the prevalence of parthenogenetic eggs during the rise of the pulse, and the evidence of sexual reproduction during its progress. In some other instances the number of free winter eggs after the 188 BRACHIONUS PALA, TYPE FoRM. SEXUAL CYCLE. Winter eggs Summer eggs 1895 | Males|Maleeggs 7 ee ind | Free* ee d Free* | Carried viduals Octs 0a: — | | ——— | =| 96. | ——— 96 48. INGN Sosc0o5)) == 765 10S | 3D 1,700 3,060 6,375 6,885 INGweel eee 4,140} 8,280 7,245 | — |-63,135 | 71,415 |150, 0755), 134555 Nova Ohara = 1,680 | ———— | — | 43,680 | 68,880 |114,240 | 189,280: INN 2 4/3)s'o4 == 742 2,226 | — | 46,746 | 89,040 1138,754 | 217,777 Dec rman wer. — 1,380 | ———— | — | 68,310 | 66,240 |135,930 | 211,830 Decrlliy Ns se == 424 | ———— | — } 16,112 | 17,384 | 22,472 36,464 IDO ashes Ghee | ave S| | 17,808 il bits) 18,921 14,469 Mec 25 sae ya eg les Sean a 371 742 371 * Includes free eggs of other varieties also. culmination of a pulse is very large. For example, the sudden ver- nal pulse of 716,982 on April 24 1s accompanied by 28,584 free winter eggs. The pulse declines to 22,224 on April 29, and the free winter eggs rise to 95,841, and the empty loricz to 26,114. Females carry 1-5 summer eggs, and 1-8, or even more, male eggs. There is great variation in the size of the summer eggs, these and the male eggs appearing almost to intergrade. Brachionus pala, including B. ampliceros, is a common constitu- ent of the plankton of shallow warm waters. It has not been reported from the larger and cooler lake waters by Apstein (’96), Burckhardt (’00 and ’00a), or Jennings (94, ’96, and ’00). Zacha- rias (98) and Marsson (’00) find it in the summer plankton of smaller lakes and ponds in Germany. Seligo (’00) records it from April to October, with a maximum in August, in Prussian lakes; and Lauterborn (’98a) finds it to be perennial and polycyclic in the Rhine. Schorler (’00) reports both pala and amphiceros from the Elbe, the former being abundant in May and sporadic during the summer, while the latter was abundant in April, June, and Septem- — ber, and rare at other times during the warmer months. Zimmer 189 (799) finds amphiceros in the Oder, where it appears in April and increases until the end of August or the first of September, when it is the most abundant animal in the plankton. In no one of these instances was the examination so long continued or made at such short intervals as in the case of the exploration of the Illinois. The diversity exhibited in these different waters may be paralleled by the fluctuations from year to year in the Illinois, and from all the data it may be inferred that the organism is probably perennial and polycyclic, the number of pulses depending upon local conditions, primarily of the food supply. Brachionus pala var. amphiceros Ehrbg.—Average number of females, 17,071; of eggs, 5,103. The numbers were much larger (158,299 and 35,392) in the stable conditions of 1897, and still smaller (5,430 and 715) in the disturbed conditions of 1896. The seasonal distribution of this variety with respect to that of the type constitutes the chief point of interest in the records. It is _ present throughout the whole range of temperatures, shares in the vernal and autumnal pulses noted for the species as a whole, but constitutes a much greater proportion of the amphiceros-pala group during the warmer months than it does in the colder ones. Thus, as shown in the accompanying table, the proportion which ampli- SEASONAL DISTRIBUTION OF BRACHIONUS PALA AND B. PALA VAR. AMPHICEROS. June 1 to Oct. 1 Oct. 1 tov jane 1 Year pala | amphiceros | pala amphiceros Pus |} up aoe) : rf bee No le 5 No. a 5 No. 2 5 No. a 8 | 3) 3) Oo ) Wee... Peed 5 52394 196. 863,247 -|71 | 336,618) 29 Paob........ | 14,637} 14| 89,400 | 86| 958,265 | 87 | 144,087). 13 LO 5 eee 14,600 | 4 | 3,776,400 | 96. | TANS O SO fe 912,580} 66 || By | APL OIER ayes ne 10,440 + 229 1 20¥ al 9G) | {2OR G26 mes 657,960 | 83 Average.....| 11,679 6.5 | 1,062,711 93.5} 667,696 | 55 |512,811| 45 190. ceros forms of this group in the period from June 1 to October 1 is from 86 to 96 per cent., averaging 93.5 per cent. in the several years. On the other hand, in the colder months—Jan. 1 to June 1 and Oct. 1 to June 1—the per cent. is only from 13 to:83, averaging 45>) The temperatures on June 1 (Pt, I., Pl. [X.—XI1.)\ average abouuejan and on Oct. 1 about 67°. The spinous form (amphiceros) thus in- cludes about 45 per cent. of the individuals at low temperatures, and 93.5 per cent. at high temperatures; and the smoother form (pala Lye) 5) Per ceny.anG (Oospermcent Tespeerively: This predominance of the spinous variety at high temperatures 1s apparently a striking illustration from statistical evidence of the hypothesis of Wesenberg-Lund (’00) that such elongations of the body of planktonts are adaptations to the lessened buoyancy of the warmer water. This relation of the spinous form to higher tem- peratures is evident in every year, 1895-1898, and the proportion of spinous forms, 86-96 per cent., exhibits all the constancy that might at the best be expected in plankton data. The relation is generally apparent (Table I.) in the individual entries as well as in the sums total, and, considering the numbers concerned and the long period of observation, should have more weight than some of the exceptions to the hypothesis, which have been or will be noted, in which the data are less extensive. For example, Brachionus pala var. dorcas does not in its seasonal distribution support the hypothesis, but owing to its small numbers—especially of the form Spinosus—less weight should attach to its evidence. In 1897 the first autumnal pulse of the pala group consisted almost entirely of var. amphiceros. This pulse started August 10 at 3,600, culminated August 31 at 1,398,000, and declined to 800 September 29. Of the 3,500,200 individuals included in this pulse, all but 11,400 belonged to amphiceros. The temperatures recorded during this period ranged from 83° to 71°. A second pulse started October 5 at 1,600, culminated October 12 at 1,605,600, and declined to 0 on October 26. Of the total individuals (1,609,000) included in this pulse, 894,800 belonged to amphiceros and 714,200 to pala. The range in recorded temperatures in this period was from 71° to 59.5°. This may serve as an additional illustration of the relation of tem- perature to the spinous variety of Brachionus pala. This variety is itself polycyclic, as is evidenced by the recurrence of male and winter eggs carried by the female at times of the pulses. 191 Owing to the ease with which such eggs are detached, the records are quite imperfect indices of the actual numbers. In 1898 male eggs (carried) to the number of 70,400 per m.* attended the culmina- tion of the vernal pulse (419,200) on May 3. Winter eggs (carried) were recorded twice on the decline of the pulse of August 16; once on the decline of that of October 25 ; andonce on that of December 15. Brachionus pala var. dorcas Gosse.—The seasonal distribution of this variety is so sharply defined that it merits especial attention. The following table gives the dates and temperatures of last and first records in each year. SEASONAL LIMITS OF BRACHIONUS PALA VAR. DORCAS. Last records First records | Largest pulses Year | Date | Temp. Date | Menmip: | Date | Temp. | No. | | | in mone) Apr.29 | 64° | Oct. 15 Bice ear. 29 164° 9,000 | Nov. 14 We ear 1896 May 1 02>) Now. 17 44° | Apr. 24 72° | 183,000 1897 | Apr. 27 GO» Oct. 12 ne5e VwArne 27 602 e200 jam. 11,798 32° | | | 1898 Apr. 26 S725 Dec. 6 |) 2@4° 1 Apr. 26 57° | 4,000 May 17 | 64° | | | The species practically disappears at the end of April, when temperatures rise above 70°, and it does not return to the plankton until they fall, in October and November. Its period of continuous occurrence does not begin in years of greatest numbers until tem- peratures reach 45°, and it remains throughout the period of mini- mum temperatures. As the collection-averages indicate, this species is relatively rare, and its numbers, even in its largest pulses, are usually smaller than those of the other varieties which 1t accom- panies. Although this species is a winter planktont it reaches its greatest development during the spring pulse, indicating an optt- mum near 65°, though it does not recur in numbers when this temperature returns in autumn. There is a single autumnal pulse in 1895 of 8,625, on November 14, at 44°, accompanying pulses in the other varieties. There was also one midsummer record. 192 The curvature of the median anterior horns which defines this variety results in a considerable elongation of these processes. With regard to the idea of Wesenberg-Lund (00) that this tendency on the part of plankton organisms to elongate in “ Balanceapparat”’ is an adaptation to the lessened buoyancy of the warmer water of summer, it must be said that 1t seems difficult to apply this hypothesis in the case of B. pala var. dorcas, which is probably a seasonal variety confined to winter months. I have no data, however, on the relative development of these processes in 6. pala,at different temperatures, beyond the seasonal limitation of this variety to lower temperatures when it should be least expected according to the hypothesis. Brachionus pala var. dorcas has not been found widely distributed in the fresh-water plankton, or at least not reported separately from 6. pala, which is widely distributed. Skorikow (’96) reports it from Charkow, Russia; and Kertész (’94), in January from Budapest. Brachionus pala var. dorcas forma spinosus Wierz.—Average number of females, 33; of eggs, 2. This form was always sporadic in its appearance in our plankton. Of 12 occurrences, 3 were in April, 2 each in November, December, and July, and one each in January, May, and August. The whole seasonal range of tempera- tures is thus included. It may be of significance for Wesenberg- Lund’s hypothesis that the spinous form of dorcas makes over 50 per cent. of its appearances between April 1 and-September 30, whereas dorcas itself is much less abundant relatively within these limits. The largest occurrence of spimosus—100,044 on April 24, 1896—was marked by the fact that 97.5 per cent. of the individuals were infested with fungi. The nearest approaches to pulses in this form are the November-December appearances in 1895 and 1896. Females with winter eggs were recorded December 29 in the latter year. Brachionus quadratus Rousselet.—Individuals corresponding to Rousselet’s description have been found occasionally in the plankton from the last of May till the middle of August at temperatures of 70° and above. The species is somewhat closely related to the bakert series, and may ultimately prove to belong to it. Rousselet (’97) is of the opinion that it is distinct by reason of the truncate posterior end, the absence of foot sheath, the reticulations of the , shell, and the semi-jointed foot. It occurred only in small numbers, 1S and forms intermediate between it and bakeri were not recorded. This is, I believe, the first record of its occurrence in American waters. Brachionus urceolaris Ehrbg.—Average number of individuals including all varieties, 468; of eggs, 56. The species was relatively quite abundant in 1897 (5,290 and 1,976) in the stable conditions then prevailing, but less so in the recurrent floods of 1896 (1,020 and 494). It is not a common species, being outranked by B. angularis, baker1, budapestinensis, and pala. The species as a whole is found throughout the entire year, though never in large numbers since 1895. The following table, which gives the principal pulses in the several years, shows the wide range S the species and its varieties in seasonal distribution. PULSES OF BRACHIONUS URCEOLARIS. Year Date Temp. No. Date Temp. No. | LP 2uls co jg te OR eR COREE aaa = ED 5 9 cha cieectOhe Ciena eae oan USOT 2 Sg ei eee Mar. 24 41° Bit Pil Apr. 17 66° 8,398 (BIEN 2 Gigs 6 \G) SERRE aR Apr. 27 60° 6,400 LSE once O0E a ae Mar. 22 Sil 2,000 Apr. 26 byl 6,400 Year Date Temp. No. Date | Temp. | No. | Date | Temp. | No. 1894 | Aug. 16 84° | 181,764 1895 June 19 80° 324,254 | es | july23 | 30° |" 10,000 | 1897 —— | ——-| —— | EE : | z. = SS Year Date Temp. No. Date Temp. | No. Date Temp. No. 1894 | 1895 | Sept. 5 | 74° 4,293 Idee. (4! || sa98| gas 1896 = |) Weoleg)| “a2 lg amos 1897 Sept. 21 (fale 121,200 Oct go? | 800 | 1898 Sept. 6 79° 5,600 Dees 13 33e| 500 194. There is some tendency, especially in later years, toward the colder months. Eight of the fifteen pulses occur below 70°, and twelve between September 1 and May 1. On account of the small numbers the pulses are poorly defined in our records (Table I.), but there are indications that they coincide in location, in a general way, with those of other Brachionideé and the Ploima asa whole. They also in many instances coincide with or follow shortly after the pulses of chlorophyll-bearing organisms, as has been noted in other Brachionide. This species, B. urceolaris, is a cosmopolite,and of general occur- rence in the fresh-water plankton of smaller and warmer bodies of water. It is reported by Weber (’98) from Swiss marshes, by Zacharias (’98) and Marsson (’00) from many smaller German waters, and by Seligo (’00), throughout the year, from lakes near Danzig, where it attains maxima in April, July, and September. Since this author includes B. angularis (B. urceolaris forma angu- latus Seligo) with his records of urceolaris, it is probable that the species in the. usual sense may have much more restricted numbers and range in his region. Kertész (’94) finds it about Budapest. It is reported as sporadic in the vernal plankton of the Elbe by schorler (’00), and is listed from the Oder by Zimmer (99m Skorikow (’97) reports it once in summer plankton of the Udy near Charkow. The species is exceedingly variable in the development of the anterior spines, and in the proportions of the body. It varies toward the bakert group, and individuals are sometimes found which seem to connect the two groups. I follow Skorikow (’96) in placing B. rubens as a variety of B. urceolarts, including in it those forms whose anterior spines are least developed. The more slender summer forms I have listed as var. bursarius Barrois and v. Daday. | From my observations on B. variabilis Hempel, I am inclined to regard it as a possible variety in the urceolaris group. In form, texture, proportions, and anterior spines it is certainly similar to this group. The presence of the posterior spines would not suffice to separate it, since these may or may not be present, and the existence of a variety of urceolaris with such spines would only present a phenomenon parallel to that observed in pala, angularts, and bakert. The quadrate foot-plate present in variabiks, which, © according to Hempel (’96),is not found in other species of them 195 genus, serves to distinguish this form, and in the absence of proof of its occurrence in forms of urceolaris as here defined I prefer to leave variabilis as a separate species. In any event it is closely related to the urceolaris group,and may ultimately be found to belong within its seasonal range of variation. Seligo (’00) has suggested that B. angularts is also a variety of urceolaris, but I do not so regard it. The averages of the different forms in the several years are given in the table on the next page, which also includes B. variabilis. The discussion of the different varieties follows :— Brachionus urceolaris Ehrbg., type.—Average number of in- dividuals, 18. The type form was not abundant in any year, and its appearances were sporadic. It was recorded in February, June, and July. It includes less than one per cent. of the individuals referred to this species. Brachionus urceolarits var. rubens Ehrbg.—Average number of indrviduals, 244; of eggs, 41. This variety was more abundant during the stable conditions of 1897 (5,290 and 1,976) and the low- water years of 1894 and 1895. It includes over 99 per cent. of all the individuals referred to this species. . It is apparently the winter form of the species. This appears clearly in its seasonal distribution in the later years, but in 1894 and 1895 it was found in summer months and in large num- bers. It is thus capable of development in the whole range of temperatures. The pulses recorded in the table on page 193 are in the main composed of this variety. It is quite abundant during the summer of 1894, attaining a pulse of 181,764 on August 15 at 84°, disappear- ing in September, and not reappearing until the April collection. It attains a pulse of 324,254 on June 19 at 80°, declines in July, then occurs sporadically until the following February. It then continues till June 6, with a pulse of 8,398 on April 17 at 66°. An isolated occurrence of 10,000 in July is the only record in the summer of 1896. It is in the November—December plankton of 1896 and the March—May plankton of 1897, and attains a pulse of only 6,400 on April 27, at 60°. It does not reappear until the 14th of the following September, in whose stable conditions a pulse of 121,200 on the 21st, at 71°, is found. It disappears October 5, and is irregularly present from January to April, with larger numbers in the latter part of the period. It is not found in 1898 (Table I.) from May 1 to Decem- (14) 78h S 77S ‘LT | 907° 6T | 1990S ST Seo 70 bl | 79S 0S (Oya! +9 eral ean tala pate es TP40L 0- F 9¢ SOF ST 902 IP AAG 0 ST AC Secale eat, = Meme eee S68T 99 OFT 9L6'T 0672'S 0) ) 9L6'T 0672 ‘S ) 0) OS eR econ ae oe omen oe ee L681 tI OLT F6P OZO'T 0) LZ L8V 986 l l Ca UN rns pe ae 9681 l SF Sse PES es yyt 0) 0 697 Cae ee O7T $e TE ESSE NS oar fs aa eer ane S68T Cocca Oot besos On Og cs 0) 0) SOCeO Ts iC Lrae 0 S OMe Sul Sean ee F681 sso & s33q o) ssa o) ss3q & s33q ro) SUWOI{D9T[ OO JO ‘ON Ivd S1]1QDtADA St4D]09IAN SNIADSANG sUaqna UEDIOaa SNUOLYIDAT [POL “IBA “IBA ul ‘NOILOATION) Add YAIWAN AOVAAAY “SITIGAVIUVA “GF ANV “SHILGLINV A GNV SIYVTIOHIAN SQNNOTHOVAG 197 ber 1, but is continuously present in the winter of 1898-99 from December 6 till March 28, when collections ceased. Male eggs were recorded but once—April, 29, 1895—-and there is no other evidence of the cycles of reproduction beyond the pulses in numbers. They suggest a polycyclic habit with major pulses in spring and fall. It is apparent that conditions affect these cycles greatly, as is seen, for example, in the contrast between the earlier years, with low water in the spring, and the later ones, when high water was longer continued. This variety, rubens, has not been widely reported in the plank- ton. Skorikow (’96) finds it in June in the River Udy, and Kertész (794) reports it from Budapest, while Stenroos (’98) finds it in the littoral fauna of Lake Nurmyarvi in Finland, and also in the plank- ton in July and August. Brachionus urceolaris var. bursarius Barrois and v. Daday.— Average number of individuals, 206; of eggs, 33. This is a sum- mer variety, and forms but a small part—less than one per cent.— of the total number of individuals referred to the species. Brachionus variabtlis Hempel.—This species was found but once in 1898, but was more abundant in former years (see table on oppo- site page). The largest development which it attained in the Illinois was a pulse of 168,222 on August 15, 1894, at 84°. The largest number in subsequent years was 5,200 per m.* on August 8, 1896. It may be significant of the connection of this form with the urceo- laris-rubens group that the great pulse of 1894 was coincident with an unusual development of rubens on that date. This species is a summer form, the earliest record being May 24, 1898, at 74°, and the latest September 25, 1895, at 73°. Its opti- mum temperatures lie near the summer maximum. If this form should prove to be merely a spinous variety of B. urceolaris it will afford another illustration of spinous varieties of Brachionus appear- ing at high temperatures, in accordance with the hypothesis of Wesenberg-Lund (’00). In Table I. there is given for 1898 the seasonal distribution of the free winter eggs of Brachionus. It will be seen that they occur throughout practically the whole year, with some increase after the times of the April-May and September pulses. Cathypna leontina Turner.—Average number, 47, in 1896, a year of disturbed hydrograph; less abundant in previous years, and not 198 recorded in subsequent ones. Earliest record, June 17, at 76°; and latest, October 2, at 63°. Always present in small numbers and evidently adventitious. Cathypna luna (Ehrbg.) Gosse-—Average number, 47. Found in every month but November, though always in small numbers and irregularly. All but six of the thirty-three records fall between April 1 and October 3 and above 50°. Over half of all the individu- als were found in 1896. This fact, together with the nature of the seasonal distribution, indicates plainly its adventitious character. Cathypna rusticula Gosse.—Found once, March 22, 1897, at 44°. Not previously reported from American waters. Celopus porcellus Gosse.—Average number, 106. From March to September, at 37° to 80°, and apparently adventitious. Colurus bicuspidatus Ehrbg.—Average number, 274. .This species is apparently a winter planktont. In 1897 it appeared first November 9, at 50°, and was found somewhat irregularly through the winter until May 17, at 64°. There is a pulse March 15, at 46°, of 6,400. Ovigerous females were found during the rise of the pulse, and males on April 12, onits decline. A few scattered records were made in the following winter, beginning November 8, at 46°. It occurs in the plankton during flood season and may be adventitious. Colurus obtusus Gosse.—Average number, 38. In small numbers and irregularly in March and April at temperatures below 50°, and in September at 73°. Hempel (’99) lists also C. deflexus Ehrbg. Diglena circinator Gosse.—Average number, 121, in 1896, a year when many adventitious rotifers were brought into the plankton - by disturbed hydrographic conditions. All the records lie between April 29, at 70°, and July 28, at 81°. Anovigerous female was found in July. The species is adventitious in the plankton. Diglena forcipata Ehrbg. was recorded once—October 12, 1897, BEL) Sian Diglena giraffa Gosse was observed but once in the river plank- ton. Not before recorded from American waters. Diglena grandis Ehrbg. was recorded in July and September at (62 ang 70>. Diglena uncinata Milne was found August 12, 1898, at 82°. Hempel (’99) reports D. biraphis Gosse and D. catellina Ehrbg. in waters immediately tributary to the river. All members of the 199 genus belong to the littoral fauna among vegetation, and are adven- titious in the plankton of open water. Euchlanis pyriformis Gosse.—Recorded April 12, 1898, at 52°. Hempel (’99) reports it from June to October in collections in the river in 1894 and 1895. Euchlamis triquetra Ehrbg.—Average number, 19. Found irregu- larly from July to November at 84° to 41°. Hempel (99) reports it also in June. It is probably adventitious. Hempel (’99) also reports EF. dilatata Ehrbg. in the river from July to September, and E. dejlexa Gosse in tributary waters. Gastropus stylifer Imhof.—A rotifer doubtfully referred to this species was found sporadically in the plankton of the river. It was recorded in June, 1894, and July, 1896, at temperatures above 75°. It was almost continuously present in 1896 from February 20 to April 10, and again on November 17 and December 3. It did not reappear until January 31, 1899, from which time it continued present until the close of operations in March. Most of these oc- _currences are at minimum temperatures and all of them below 45°. I have followed Weber (’98) and Jennings (’00) in using Imhof’s name Gastropus stylifer instead of Hudsonella picta Zach. or Notops pygmeus Calman, by which names the species has been frequently designated. The evidence from our records indicates that it is a somewhat sporadic winter planktont in our waters. Lauterborn (°93) finds it to be a perennial planktont in the Rhine, with its largest numbers in summer. Hydatina senta Ehrbg. was found September 20 at 73°. Hempel (799) also reports it in towings from the river in March and July, 1895. This species is very common in European waters, but has as yet been found in America only in the Illinois River and, by Kel- licott (’88), at Corunna, Mich. Mastigocerca bicornis Ehrbg.—Average number, 42. Found irregularly and in small numbers from June 28 to September 13 above 63°. Hempel (’99) reports it from Quiver Lake among vegetation, and it is evidently adventitious in the river plankton. Mastigocerca bicristata Gosse was found but once, late in Septem- ber, 1895, at 73°, but it is more abundant in the backwaters. Mastigocerca carinata Ehrbg.—Average number, 1,674. This Species was present in the plankton from the middle of June till the 200 first of October, and at irregular intervals and in small numbers in fall and winter months. The distribution in years prior to 1898 falls within the limits shown in Table I. In this year the bulk of the occurrences lie between June 21 and August 4, and above 77° and 72°. The optimum lies near the summer maximum, though occurrences at minimum temperatures in March and December reveal acclimatization to a wide range of temperatures. In this year there are several somewhat irregular pulses, the best-defined of which follow the pulses of chlorophyll-bearing organisms (cf. Table I. and Pl. II.) at an interval of one or two weeks. The species was not recorded so frequently in previous years, in some of which also pulses are indicated. These pulses are not consequent upon floods, and the species is apparently not adventitious in the plankton but a normal constituent. Apstein (’96) reports WM. capucina as abundant in Dobersdorfer Lake from June to October—a seasonal distribution similar to that found in the Illinois River for M. carinata. Masttgocerca elongata Gosse was found once—March 28, 1899, at 38°. Hempel (99) reports it in June in Quiver Lake. Mastigocerca mucosa Stokes was taken in August to October, 1898, at 82°-62°, in small numbers. It is reported by Jennings (700) as “one of the most abundant of the Rotifera among the vegetation of the shallow parts of Lake Erie,’ but it was not reported by Hempel (799) in similar environment about Havana. Mastigocerca stylata Gosse was found in the plankton in small numbers in June and July at temperatures approaching 80°. Hempel (’99) reports it also in August. In addition to the species of this genus above listed, Hempel (’99) records VM. lata Jennings. There are also in our records a considera- ble number of individuals referred to this genus but not specifically identified. Many of these belong to one, or possibly several, very small species. They are most abundant during the summer months, reaching a pulse of 16,800 on June 28. They occur in large numbers in the filter collections (average for 1898, 798; filter-paper, 145,384), and, it seems, must escape pha ease through the silk net on account of their small size and their active movements. A number of species in this genus have been described of late from the fresh-water plankton, but in the present state of the litera- ture of the subject I am not certain to what species these forms 201 should be referred. The genus is sadly in need of critical revision. It includes a number of semi-limnetic species, whose importance in the plankton will probably be revealed by more perfect methods of collection. Metopidia lepadella Ehrbg. was found only in March and June at temperatures above 46°. It 1s apparently adventitious. Metopidia oblonga Ehrbg. was found once—July 29, 1895, at 75°. Metopidia salpina Ehrbg. was recorded June 28, 1898, at 78°. Metopidia solidus Gosse.—Average number, 67. This is the most abundant representative of the genus in our plankton. It was recorded from March 15 to November 14, at temperatures above 45°. Most of the occurrences are in the summer months (Table I.), at maximum temperatures. The numbers are small, the occurrences irregular, and the species evidently adventitious. M. rhomboides Gosse is recorded by Hempel (’99) from the river plankton, as also M. acuminata Ehrbg., triptera Ehrbg., and bractea Ehrbg. from the backwaters. Monostyla bulla Gosse.—Average number, 50. Present in small numbers and irregularly from April till the middle of October at temperatures above 50°. It is evidently adventitious. Jennings (700) finds this one of the most abundant rotifers among the aquatic vegetation in Lake Erie. It is in our waters the most abundant of the genus in the plankton, especially in the vegetation-rich back- waters. Monostyla lunaris Ehrbg.—Average number, 37. Found in the extremes of the temperature range, but over 50 per cent. of the occurrences are in August—-October. Its numbers are always small and its occurrences irregular. It is plainly adventitious. Monostyla quadridentata Ehrbg.—Average number, 10. This species was found in the plankton irregularly in July-September, at maximum temperatures. It is abundant (Hempel, '99) in the backwaters, where vegetation is abundant, and is apparently adven- titious in the plankton. In addition to the species here recorded Hempel (799) lists M. cornuta Ehrbg. and M. mollis Ehrbg. from collections in the river,and WM. closterocerca Schmarda from the back- waters. This is an exceedingly variable group, and will repay a thorough revision in the light of a study of the variation of its species. A considerable reduction in the number of these so-called species will doubtless result from such a study. 202 Noteus quadricornis Ehrbg.—Average number, 19. This is a rare species in the plankton, being found in 1895 and 1896 in July at maximum temperatures, and in 1898, on April 12, at 52°, and on November 8, at 46°. Notholca longispina Kell.—This species, which has been found in the summer plankton of many European and American waters, especially our Great Lakes, was noted but once in the [llinois—in January, 1895 (Hempel, 99). It seems to prefer cooler and purer waters. Notholca striata Ehrbg.—Average number, 437, including varie- ties. This is a winter planktont in our waters, appearing in 1897 on November 30, at 34°, reaching a maximum of 10,840 March 22 (Table I.), at 51°, and disappearing April 19, at 52°. It reappears the following autumn on November 1, at 45°, and attains a maxi- mum of 4,000 March 21, at 37°. In previous years the occurrences all lie within the limits of November 1 and April 24 with the excep- tion of two records in 1895—September 5 and October 15, at 74° and 56°. The spring maximum in 1896 (7,778) was on April 10, at 52°, and in 1897 (4,260) on March 22, at 43°. In each» year Bite single pulse, that of March—April, is indicated. Minor fluctuations during the winter (Table I.) are in some cases attributable to flood agencies. The temperature limits of this species are quite definitely estab- lished. The species reappears in autumn when 45° is reached, and declines rapidly in the spring after 50° is passed and is but rarely found above 60°. It attains its greatest numbers late in winter or early in spring in the face of flood conditions, though the numbers attained in the channel waters are never very large. Empty loricee have been found in the plankton after the decline of the species in April, and females with a single egg were noted in small numbers in 1895 during the rise of the pulse. I follow the suggestion of Weber (’98) that N. striata should include as varieties the following: N. labis Gosse, N. jugosa Gosse, and N. acuminata Gosse. Examination of many individuals in the plankton proves beyond a doubt the great variability of the organ- ism whose seasonal occurrence we have traced. It varies in the length of the posterior spine, in the proportions of the lorica, and in the development of the strize and the anterior spines. Of a total of 81,227 of Notholca striata in this wider sense, 68,887 were referred 203 to var. acuminata, 3,852 to var. jugosa, 7,029 to N. striata in the narrower sense, and 1,469 to other varieties, including var.labis and var. scapha. The seasonal distribution of N. striata (sensu strictu) and var. jugosa lies within the limits of that of var. acuminata, but occurrences are too few to trace their seasonal fluctuations. This species is reported by Lauterborn (’94) in the winter plankton of the Rhine. He also notes the connecting links between N. acuminata, N. striata, and N. labts, and regards them as belonging to the same “ Formenkreis.’”’ Apstein (’96) reports N. acuminata, N.labis,and N. striata in lakes of northern Germany and indicates a seasonal distribution which coincides closely with that found for these forms in the waters of the Illinois. He also reports a March— April maximum and only isolated occurrences in midsummer. Forbes (’83) finds the species in the stomachs of young Coregonus feeding upon the March plankton of Lake Michigan. Seligo (’00) also finds it in the winter plankton of Prussian waters. Notommata cyrtopus Gosse was found in the plankton in April _and September at temperatures above 50°. Hempel ('99) reports N. aurita Ehrbg. from the river, and N. tripus Ehrbg.and N.lacinu- lata Ehrbg. (=Diaschiza lacinulata Ehrbg.) from the backwaters. Plesoma lenticulare Herrick was found in the plankton of the river from September to December, 1896, throughout the whole range of temperatures from 75° to the winter minimum. Hempel (799) reports it from May to December, but principally in vegetation Polyarthra platyptera Ehrbg.—Average number of individuals, 86,674; of eggs, 52,560. In 1897, 94,653 and 58,235; in 1896, 29,653 and 11,138: in 1895, 28,947 and 20,074; in 1894, 743 and 217. The effect of the stable conditions of 1897 and of the recurrent floods of 1896 is seen in the larger averages in the former year and in the smaller ones in the latter. This is one of the most abundant rotifers in our plankton, includ- ing, as it does, one seventh of the total Rotifera, and exceeding in numbers all other species of the group excepting only Syncheta stylata. It isa perennial form, and was recorded in every plankton collection but two, and it may have been present then. The seasonal distribution of this abundant species is very char- acteristic of the form which most, though not all, plankton organ- isms exhibit. Two prominent features are (1) a limitation of large numbers to the warmer months and (2) a rhythmic occurrence of 204 recurrent pulses at approximately monthly intervals. In Plate V. I have plotted the seasonal distribution of this species for the years 1894-99. The plate will serve as one of the best illustrations of the nature of the data contained in my statistical records that could be chosen from them. It illustrates graphically the character of the seasonal distribution of this species and the nature of what I have called recurrent pulses. In the table which follows, as elsewhere in similar tables, these pulses are listed by the number of individuals attained at their maxima, and are located according to the dates of these maxima. PuLsES OF POLYARTHRA PLATYPTERA. Year Date Temp. No. Date Temp. No. Date Temp. No. 1895 = = SS —=——= aS ———— a 1896 Jan. 6 ae) 5,406 | Feb. 25 34° 7,852 | Mar. 24 41° 57,267 a INS) 338 2136 1897 — = === Ses = ————— 1898 Jat 25 ove 11,997 Feb. 22 o2e 6,318 == = 1899 Jan. 17 Som 20,800 | Feb. 14 SS 145,600 | Mar. 7 339 71,200 Year Date | Temp. No. Date Temp. No. Date Temp. No. 1895 Apr. 29 64° 86,867 SS 1896 Apr. 24 122 233,436 May 8 76° 54,365 | June 1 69° 18,000 oo all 18° 35,200 1897 Apr. 27 Ge || ioe) | ———= aoe 1898 Apr. 26 572. 696,000 | May 17 64° 195,200 | June 14 82° | 432,800 Year Date Temp. No. Date Temp. No. Date Temp. No. | i} 1894 July 30 82° iL SOs | ——= == - 1895 Jalyavo Sie 231,504 | Aug. 1 79° 6,350 | Sept. 12 79° 19,272 ch aL 82° BIZ Sil 1896 July 10 80° 90,000 | Aug. 8 86° ZO, 100) || = == | ———— as} 82° 71,000 1897 July 21 81° 172,000 | Aug. 24 78° 230,400 | Sept. 14 83° 50,000 1898 Aug. 2 78° 288,000 | Sept. 27 73° | 238,400 Hae 77} 822 96,000 ‘yamke 205 PULSES OF POLYARTHRA PLATYPTERA—continued. 3 : : Year Date Temp. No. Date Temp. | No. | Date |Temp. | No. | | 1894 | Oct. 17 58° 1,140 | = 1895 | Oct. 23 51° 408 | Nov. 27 33° | 74,942 | Dec. 18 39° | 21,147 1896 eee Dec. 29 35° | 37,560 1897 | Oct. 5 71° | 816,000 | Nov. 15 47° | 22,400] Dec. 14 40° | 7,300 1898 | Oct. 11 65° | 47,500 | Nov. 22 40° 6,000 | Dec. 20 33° | 63,400 "25 49° | 37/500 An examination of this table and the graphic presentation (PI. V.) of the seasonal distribution will show at once the uniformly small numbers attained at low temperatures. Between October 15 and April 15, that is below 60°, no pulse exceeding 100,000 is reached save one of 122,400, February 21, 1899, at 33°. Of all the records in this period only seven exceed 50,000. On the other hand, during the warmer months, above 60°, the pulses have a much greater amplitude. Four of them exceed 400,000, and there are twenty-two records above 100,000. The summer pulses are often separated by minima which approach midwinter levels, but in spite of this the general level of summer occurrences is much higher than that of the colder season. In 1898 the average from April 15 to October 15 was 30,861 per m.*, and for the other months of the year, 15,813, or about half the number in the warmer season. From these facts of distribution it is apparent that though perennial the species finds its optimum conditions at temperatures above 60°. The statement of Hempel (’99) that it thrives best in cold water is not borne out by the statistical examination in any of the years. The recurrent pulses of this species vary greatly in amplitude. The largest pulse recorded was that of 816,000, October 5, 1897, at 71°. It appeared in a period of prolonged low water and at the close of one of high temperatures continued beyond the usual - September limit (Pt. I., Pl. XI.), in a very unusual development of Carteria and the smaller alge of the water-bloom (Pl. II.). Similar autumnal pulses do not appear in other years, the autumnal develop- ment as a rule not exceeding to any noticeable degree that of mid- summer. There has been in every fully tested spring a large vernal pulse, usually at the time of the spring volumetric maximum, or thereabouts.. In 1896 and 1898 it was the largest pulse of the year. 206 This was not true in other years, but collections in those years were too infrequent to trace the seasonal distribution of the species with accuracy at that season. It is volumetrically of some importance in determining the quantitative fluctuations in the total plankton. Computations based on its average size indicate that approximately 600,000, including eggs, would be required to form 1 cm.* of plank- ton. On this basis, and allowing 10 per cent. for interstices, it constituted at the time of its vernal maximum in 1898 about 10 per cent. of the total volume of the plankton (silk-net catch). The table on pages 204 and 205 lists 43 pulses, of which 6 lie out- side of the period included in Plates I.and II. Of the 38 remaining pulses 16 coincide in location with the whole or a part (in case of divided culminations) of the pulses of the chlorophyll-bearing organ- isms; 12 follow at the next collection, usually at intervals of one week; and 6, after a fortnight. The remaining 4 do not bear this rela- tion, occurring in autumn or midwinter, when all pulses were feeble and ill-defined. A comparison of Plates I. and II. with V. will show that not all of the chlorophyll-bearing pulses are attended by pulses of Polyarthra; nor is there any constant relation, excepting the vernal pulse, between the size of the pulses of the two groups of planktonts in question. Nevertheless, the dependence of the recurrent periods of rapid multiplication of Polyarthra upon the rhythmic occurrences of the chlorophyll-bearing organisms upon which they: largely depend for their food is strongly suggested by the data here offered. Food relations thus dominate the repro- ductive cycles. The pulses of Polyarthra forma considerable portion of many of the pulses of the total Plowma, and it is but natural that we should find a coincidence in their locations. This may be followed for 1898 in Table I. Ina number of instances the culminations of the pulses are not exactly coincident, but separated by the interval between two collections. The association of the two pulses is, however, apparent in every case, and a similar relation may be traced in prior years. These recurrent pulses afford evidence for the polycyclic habit of this species. Additional proof of this phenomenon is found in the evidences of sexual reproduction—either male or winter eggs attached to the female—which have attended many of the pulses. The eggs of this species, both summer and winter forms, are very 207 readily detached in the manipulation of the plankton, so much so that in 1898 less than 6 per cent. remained attached. More or less uncertainty attends the determination of the parentage of detached winter and male eggs, so that decisive proof of sexual reproduction is best obtained from the attached eggs. In Table I. will be found the records of free and attached male and winter eggs recorded in 1898. Evidence will be found in this of sexual reproduction at- tending the pulses of March, April, May, September, and December. The presence of winter eggs at intervals throughout the greater part of the year may be due either to their continual production or, as seems more probable, to their continuance in the plankton for some time after their formation. The presence of attached winter eggs, or of larger numbers of free winter eggs, seems to mark the culmina- tion and decline of the pulse. Male eggs, on the other hand, are more generally present during both the rise and decline of the pulses. Somewhat similar evidence of sexual cycles attends many of the larger pulses in years prior to 1898. This species affords a striking example of a perennial eulimnetic planktont. It is found in midwinter under the ice in water at the freezing point, and even under these conditions it multiplies, pro- ducing pulses whose amplitude surpasses that of many rotifers of the plankton, and runs a reproductive cycle similar to, though of less amplitude than, those at other seasons of the year. It shares with other organisms the vernal outburst, and repeats the process in summer months under maximum conditions of heat and in waters whose chemical condition is very different from that in which the hiemal and vernal pulses appeared. Successive generations of this Species are thus adapted to widely different conditions. Through all the changes incident to ice, stagnation, flood, sewage pollution, changing temperature, the wax and wane and change of food, the constant and unceasing warfare of enemies which prey upon it and of parasites which plague it, and, above all and continuously, the removal of countless individuals from the place of their origin by the ceaseless current of the stream, this species lives on, holds its own in the plankton, and repeats year after year the same sequence of rhythmic pulses of occurrence in the river water. The secret of the process doubtless lies in its capacity to produce repeatedly these crops of winter eggs which serve to seed the environment and start 208 - anew the cycle of growth and reproduction whenever the favorable conditions prevail. There is in this species no hard lorica whose variable processes might serve to demonstrate to every observer its capacity for varia- tion. This is doubtless one of the reasons why we do not find a host of new species and varieties of Polyarthra as in the case of Brachionus. It is subject to considerable variation in size,and the swimming lamelle vary in length, width, and serrations. Hempel (’99) records Wierzejski’s var. euryptera in our plankton, and I have often observed it, but no record was kept of it since the characters which define it are not readily seen in plankton enumeration. Weber (’98) has mentioned, without designating by name, a long-spined variety which I find very common among the individuals which occur in the Illinois. This planktont is subject to attacks of internal parasites (Sporo- zoa?) which infest it at the times of its maximum pulses, though never to the extent observed in the case of Bimerium in Brachionus. It is very frequently loaded down by Colacium, and some of the smaller peritrichous Czliata are often found upon it. The absence of a hard lorica has served to obscure somewhat its food relations to whatever animals prey upon it. Polyarthra platyptera is a cosmopolite, and is apparently found generally in the fresh-water plankton. Jennings (’00) reports it as abundant in the waters of the Great Lakes, and it has been found generally in American waters. Zacharias (’98) and Marsson (’00) find it in pond and stream waters of Germany; Stenroos (’98) reports it asa predominant rotifer in the planktonand littoralregions of Finland waters; and Borge (’00) finds it in Swedish plankton. It has also been found to be an important constituent in the plankton of European streams. Skorikow (796) finds that it 1s the most abundant rotifer in the summer plankton of the River Udy, consti- tuting almost a third of the total rotifers. There are indications in his records of recurrent pulses, and the largest numbers are found in September. Zimmer (’99) finds it perennial in the Oder, but never abundant. Schorler (’00) finds it in the Elbe from April to September, with maximum in August. Lauterborn (’98a) lists this species among the perennial rotifers,and states that it is dicyclic in the Rhine and its adjacent waters, which he has examined quite thoroughly. The vernal sexual period begins with the appearance Ges ici 209 of the male eggs in March, and winter eggs follow in April and May. The second sexual period extends from the end of July to the end of October, with a maximum in September—October. This bears some resemblance to the distribution in the Illinois, with the _exception that the recurrent cycles which make the species poly- cyclic were not noted, and that male or winter eggs were not present in the colder months. It may be that the application of the quantitative statistical method with brief intervals of collection in the Rhine would reveal a still closer correspondence in the seasonal routine of Polyarthra in the two streams. Wesenburg-Lund (’98) finds that temperature has nothing to do with the appearance of the sexual cycle of this species in Danish waters. Males were found in December, as also (eggs only) in the Illinois. He also found differences in different bodies of water as to the times of the sexual cycles. Apstein (’96) has found this species perennial and one of the most abundant rotifers in plankton of the lakes near Plon, Germany, with maximum period from April to August, and in November in one lake, and in July-August in another. The ’ sexual cycle was noted in May-June only. Seligo (’00) finds the species perennial in lakes near Danzig, with large numbers in April and July. His collections were too widely separated to trace fully the seasonal fluctuations. Burckhardt (’00a) finds Polyarthra in small numbers in winter months in the plankton of Swiss lakes, and in larger numbers in the summer, but does not trace their seasonal fluctuations. Pterodina patina Ehrbg.—Average number of females, 37. With two exceptions all the records of this species lie between the last of May and the first of October. There are but four records below 70°. This indicates optimum conditions for the species during the period of maximum heat, and further evidence of this les in the occurrence of the larger numbers during this period. Appearances in January—March suggest a perennial habit; and small and irregular numbers, that the species is largely adventitions. Hempel (’99) also records P. valvata Hudson from Quiver Lake. Rattulus tigris O. F. Mull—Average number of females, 207. I have not found this species in any year later than October, though, as shown in TablelI.,it appears in January at minimum temperatures, and continues in small numbers and somewhat irregularly until autumn. These conditions and the absence of pulses suggest that 210 the species is adventitious in the plankton. The greater part of the occurrences were recorded above 50° and the larger numbers above 60°, indicating an optimum during summer months. The record in Table I. refers to the species figured by Jennings (’00) under this name. Rattulus sulcatus Jennings was found seven times in the plankton in July and August during maximum temperatures. It is probably adventitious in the plankton. Salpina brevispina Ehrbg. was found September 5, 1895, at 74°, and April 29, 1896, at 70°. Salpina eustala Gosse was found July 13, 1894, at 82°. Salpina macracantha Gosse was found September 5, 1895, at 74°. Salpina ventralis Ehrbg. was found July 29, 1895, at 75°. In common with other species of the genus it 1s adventitious in the plankton. : Schizocerca diverstcornis v. Daday.—Average number of females, 46. The earliest record of this species was June 1, 1896, at 70°; and — the latest, September 20, 1895, at 78°. Most of the records and the larger numbers are in July-September during the period of maximum heat, in which its optimum conditions must be found. Egg-bearing females were also found in these months. This species is closely related to the Anurea aculeata group, and like it is exceed- ingly variable, especially in degree of development of the various spines. Variety homoceros Wierz. was found in May, June, and August, 1896. Five sixths of all the individuals recorded were found in 1896, and the fact that this was a year of unusually dis- turbed hydrograph (Pt. I., Pl. X.) suggests that this form may be to some extent adventitious in our plankton, but no direct relation to the access of flood waters can be traced. Lauterborn (’98a) lists this speciesamong the summer planktonts of the Rhine, and Seligo (’00) finds it in large numbers, with a maxi- mum in July, in lakes near Danzig. Zacharias (’98) reports it in German pond plankton, Zimmer (’99) finds it in the Oder, and Schorler (’00) in the summer plankton of the Elbe, Syncheta pectinata Ehrbg.—Average number of individuals, 3,950; of eggs, 13,823. It was much more abundant in previous years, averaging in 1897 23,227 and 28,230; in 1896, 7,064 and 7,927; in 1895, 13,071 and 4,730; in 1894, 7,520 and 1.65933 effect of the disturbed hydrograph of 1896 is seen in the smaller 241 numibers of that year, while the larger numbers in 1897 may be attributed to the more stable conditions. The small numbers in 1898 do not seem to be correlated with any feature of the environ- ment. This species has been found in every month of the year, and is thus perennialin our plankton. As will be seen, however, in Table I., the most of the occurrences and a much greater proportion of the individuals are found between May and October, and thus above 60°. The same limitations are found in the other years, with the exception that in 1896 there was a more continuous and larger de- velopment from the last of February. In the table which follows it may be noted that all of the pulses but four are at temperatures above 70°, and of these four none exceeds 25,000, and two do not exceed 2,500. The optimum conditions for the species in our waters are therefore above 70°. The average temperature at the time of the larger pulses is near 80°. The vernal pulses are poorly defined, as are likewise the autumnal ones. It is a midsummer species in our waters, with its maximum in August. PULSES OF SYNCHETA PECTINATA. Year Date Temp. Noy, = Date Temp. No. Date Temp. | No. 1894 ——== SS | = -S |d = S| === —S | == 1895 —— — ——— —_| —- 1896 Mar. 3 aoe 6,360 Apr. 10 46° Pe ANG Yo) || —<————— === | == 1897 == —— ——— = 1898 == S| Apr. 26 57° 1,600 | June 21 has. 112,000 l Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 | July 13 83° | 74,606 1895 | July 23 | 80° 1,749 | Aug.12 | 85° | 175,230] Sept.12 | 79° | 27,740 1896 | Julyio | 80° | 22,200 | Aug.26 | 75° 50,400 «" 93 | 82° | 38,000 1897 eres _ Aug. 10 | 81° 83,200 “" 94 | 73° | 264,000 | 1898 | July19 | 84° | 20,800 | Aug. 2 | 78° 12,000 | Sept. 27 | 73° | 30,400 “93 | 82° 3/200 1898 Dec. 13 Shape 2,500 212 Of the 18 pulses listed in the preceding table 17,fall within the limits of periods included in Plates I. and II. Of these 17 there are 7 which coincide with, and 9 which follow shortly after, the culmina- tion of the pulses of the chlorophyll-bearing organisms, while 1, a small one in March, 1896, shows no such correlation. Food is thus a primary factor in the production of these recurrent pulses. As will be seen in Table I.,these pulses uniformly coincide with those of the total Plowma, and a similar relation may be followed in prior years. The eggs of this species are not usually carried by the female for any length of time, and are rarely found attached in preserved material. For this reason the sexual cycles are not easily followed with accuracy in the statistical data. It may be seen in Table I. that the free winter eggs belonging to both species of Svucheta are most numerous in the period of the larger pulses, and that their occur- rences show some tendency to coincide with these pulses. Proof that these pulses terminate in sexual reproduction is thus lacking, though it seems probable from some of the evidence. Syncheta pectinata has not been widely reported from American waters. Jennings (’94) finds it in Michigan and Kellicott (797) in Lake Erie, but it has not been elsewhere reported in American plankton. It appears, however, in many European records. Skori- kow (’96) finds it in the summer plankton of the River Udy, in Russia; Zimmer (99) finds it in common with S. tremula in the Oder throughout the year. He makes the statements that it is never rare, 1s somewhat more abundant in the spring, and is, at other times, present “in relativ gleichmassiger Haufigkeit.”’ In the light of our results it seems probable that the data at Zimmer’s disposal were insufficient to justify his conclusions as to the uniform- ity of its seasonal distribution. Schorler (’00) finds it in the Elbe in April, May, and October, with a maximum in May. Lauterborn (’98a) finds it perennial in the plankton of the Rhine, and lists it among the dicyclic species with two periods of sexual reproduction, one in April and one from the end of July to October. Judging from the character of the statistical data which have been presented for this and other species in the Illinois it seems probable that the later period noted by Lauterborn may include several cycles, and that the species is usually a polycyclic one. Seligo (’00) reports it perennial in waters near Danzig, with largest numbers in April and 213 September. Apstein (’96) finds that this species (including S. tremula and S. grandis) is one of the most abundant in lakes near Plon, with variable maxima in different bodies of water. He finds it perennial in one case, and reports vernal maxima. Winter eggs were found in March and April. Syncheta stylata Wierz.—Average number of individuals, 120,391; of eggs, 17,797. In 1897, 42,577 and 9,127; in 1896, 24,099 and 5,125; in 1895, 155,880 and 2,418; in 1894, 8,582 and 132. This species affords an exception to the general rule hitherto observed among the rotifers of our plankton in that it is more abundant in 1898 than in the previous year. As will be seen in the following table both the vernal and autumnal pulses are unusually large in 1898, while in the previous year the vernal pulse is only moderate and the autumnal pulse is scarcely to be detected. For some reason the prolonged low water and sewage contamination of the autumn of 1897 was not favorable to the usual growth of this species. It may be that it was crowded out by the unusual develop- ment of Polyarthra at that season (Pl. V.). PULSES OF SYNCH2ETA STYLATA. Year Date | Temp. No. Date | Temp. No. Date | Temp. | No. 1894 —— —_— | +—__ | ——— -_— —— | —— — | ——— 1895 = a a eee 1896 | Jan. 6 eh ROE ear a eta jie A GE 25 33> 3,648 1897 ee 1898 Nan; 25 Sur 4,257 | ———— <== = || WER om 6,400 Ze 519 58,000 1899 Jan. 14 34° 12,000 Feb. 14 322 19,200 Mar. 21 3ie 5,600 Year Date Temp. No. Date Temp. No. Date | Temp. | No. | | 1894 orn q 1895 Apr. 29 64° ZA9SA23 | “Sak ay 1896 Apr. 29 70° 380,586 | May 25 | (fe 10,800 | June 17 | 76° 79,200 1897 | ——| ———|]| May 25 | 66° | 643,680 | | Se es et ae 60° 11,139,000 | June 21 77° | 795,200 | ess 70° 61,600 214 PuLses oF SYNCHAETA STYLATA—continued. Year | Date |Temp. No. | Date | Temp. | No. Date Temp. No. | | | | 1894 | —— SS = | 1895 —— | — — | Aug. 1 79° 10,287 | Sept. 27 (phe 12.235 1896 = Aug. 8 86° 3,400) | —_ 1897 july 21 81° 103,200 Sept. 7 80° 28,000 1898 July 19 84° 64,800 | Aug. 2 79° 170,400 | Sept. 27 (fs 265,600 Mer PAE} 82° 24,800 Year | Date Temp. No. Date Temp. No. Date Temp. No. | 1894 | Oct. 17 58° | 63,935 —_+ | FAC oy eta psec cee cg LT Pi eG 33° | 901,901 | Dec. 11 32° | 1,121,056 1896 | Nov. 17 44° | 114,000 | 1997 | Oct. 5 71° | 12,000 | Nov. 9 50° | 26,400] Dec. 14 36° 72,200 «49 65° | 15,.800| “ 30 | 34.5°| 87,200 1898 | Oct. 25 49° | 824,500 | Nov. 15 41° | 110,000 | Dec. 6 34° 42,500 “" 99 33° 59200 This is the most abundant of all the rotifers in our plankton, exceeding by 30 per cent. Polyarthra, the next in abundance. It constituted one fifth of the total Plowma in 1898, and is accordingly a large factor quantitatively and ecologically in the economy of the plankton of the Illinois River. It is a perennial planktont, occurring in six sevenths of our collections and usually in considerable numbers. The distribution in 1898 (Table I.) is a fair index of the usual seasonal routine, with the exception that in all prior years the July-August minimum 1s more pronounced and better sustained. The development in January—February is never large, rarely exceeding 20,000. In March, numbers rise rapidly, usually with a minor pulse, the re- covery from which in April culminates in a vernal pulse, which in three of the six years was the largest of the year. Following this vernal pulse there is a series of smaller pulses throughout the sum- mer. The decline of the June flood, when this occurs, seems to offer favorable conditions (cf. foregoing table and Pt. I., Pl. IX.—XIL.) for the development of a pulse which is but little smaller than the vernal one. It may be of some significance that this pulse and the a 215 vernal one both occur on the decline of the major floods of the year, and that the relative proportions of the two floods are to some degree paralleled by the amplitude of the pulses of Syncheta which attend their decline. The effect of the impounding backwaters as reservoirs for the greater development of the plankton is suggested by these data. Following the midsummer minimum is an autumnal pulse whose amplitude and location alike are subject to much variation. Aswill be seen in the table on pages 213 and 214, the maximum autumnal pulse is located twice in October, twice in November, and once in Decem- ber. This may be due to the fact that the collections are insufficient in some of the years, or to the probability that any one of several recurrent autumnal pulses may be the major pulse of that season. An examination of the seasonal distribution in 1898 (Table I.) and of the location and temperatures of the pulses recorded in the table on pages 213 and 214 will suffice to demonstrate the capacity of this species to develop at all temperatures within the seasonal range. The largest pulse (1,139,000 on May 3, 1898) is at 60°, and the next in size (1,121,056 on December 11, 1895) is at 32°. It will, however, be seen in the two tables that the pulses and the numbers in general during the periods of maximum heat and cold are not so large as in the intervals of more moderate temperatures. The impetus of the autumnal development may carry some of the pulses over in to minimum temperatures, but the level of development declines thereafter. There is thus something of a tendency for the average temperature of the larger occurrences to approach the average temperature of the year. The number of pulses listed in the table on pages 213 and 214 1s 38. Of these, 34 fall within the period included in Plates I.and II.of the pulses of chlorophyll-bearing organisms. Of the 34 there are 18 which coincide in location with these plant pulses, 12 which follow at a brief interval, and 4 which bear no such relation, three of the last being minor winter pulses. The dependence of the recurrent periods of rapid multiplication of Syncheta—the most abundant rotifer of the plankton—upon the rhythmic increase of the food supply is thus fairly demonstrated. The coincidence of the pulses of Syncheta with those of the total Ploima is readily seen in Table I.,and is equally apparent in prior years. 216 Eggs of this species are not carried by the parent for any length of time, so that reproductive cycles are not easily traced. The total number of the summer eggs of Syncheta will be found (Table I.) to fluctuate somewhat with the pulses of the species. The free winter eggs, belonging probably to both species of Syncheta, also show some tendency to predominate at and after the culmination (Table I.) of the pulses. A female carrying a male egg was recorded during the rise of the spring pulse in 1898, and attached winter eggs were noted at the vernal pulse in 1895 and 1897. The evidence points toward the culmination of these pulses in a sexual cycle. The soft and flexible nature of this rotifer and the absence of spinous outgrowths have made whatever variability the species possesses less evident than it isin such a genus as Brachionus. There is considerable variation in size—possibly due to age—even in the same collection. The determination of preserved material of this genus is fraught with insuperable difficulty. The separation of pectinata and stylata in our records is at the best only probable. It may be that other species of Syncheta have been included with the individuals referred to stylata. In any event the result of the division has led to symmetrical results comparable with those of other planktonts. Syncheta is often parasitized at the times of the larger pulses by some sporozoan (?). At the maximum of the vernal pulse in 1898 over 4 per cent. of the individuals were thus affected, the infestation continuing through the decline of the pulse. External parasites, Colacitum and Rhabdostyla, are rare. This species has not been found widely in the plankton, possibly because of the confusion of stylata, tremula, and pectinata in identifi- cation. From the large numbers reported in almost every instance where it has been found, the expectation of its wide-spread occur- rence is at least raised, waiving in this connection the possibility of specific confusion. Jennings (’94) found it to be very abundant in towings in Lake St. Clair, and (’96) in Lake Michigan near Charle- voix. He finds it less abundant in the summer plankton of Lake Erie (’00). Stenroos (’98) reports it as one of the most abundant limnetic rotifers in Lake Nurmiyarvi in Finland in the summer, and Skorikow (’97) finds that next to Polyarthra it is the most abundant - rotifer in summer months in the River Udy near Charkow, Russia. His figures of occurrence show some traces of recurrent cycles in these months, with maximum numbers at the first of August. Lau- 217 terborn (’98a) lists it among the summer rotifers of the plankton of the Rhine. The genus is in need of a thorough revision in the light of possible variation.* Taphrocampa annulosa Gosse.—Average number, 71. Found in September, at 73°. . Evidently adventitious. Triarthra longiseta Ehrbg.—Average number of individuals, 3,147; of eggs, 293. This species was about twice as abundant in the stable conditions of 1897, and was present in less than half these numbers in the recurrent floods of 1896. It is a perennial species, having occurred in every month of the year. The continuous occurrences and the larger numbers lie in all years between May and October and above 60°. In 1898, only about 3 per cent. of the total individuals were found below this temperature. With the exception of the vernal pulse of 1898 all of the larger numbers were found in the period of maximum heat. The optimum conditions for this species are thus found within that period and above 70°. The seasonal routine of the species is varied somewhat from year to year. There is usually a slight vernal pulse—larger than usual in 1898—and this is followed by recurrent pulses throughout the summer. The season closes without a predominant autumnal pulse, and after September the numbers fall and the occurrences become sporadic until the following April. The pulses of this species are listed in the following table, which gives their locations and temperatures. Of the 21 pulses recorded, 18 are within the periods of the plant pulses shown in Plates I. and II. Of these 18 there are 8 which coincide with these plant pulses, 9 which follow after a short interval, and 1 which shows no such relation. The dependence of the pulses of Triarthra upon food conditions is suggested. The pulses of Triarthra will be found on examination of Table I. to coincide in 1898 in the main with those of the total Ploima. The pulses are never very large, and the evidences of reproduc- tion are not well defined. Attached summer eggs attend the larger pulses, and free winter eggs of the species were found in October— November in-1898. In previous years free or attached eggs attended vernal or summer pulses at times. The evidence indicates a poly- cyclic habit. * See Rousselet, ’02. 218 PuLses OF TRIARTHRA LONGISETA. Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 = == 1895 Apr. 29 64° PD BX —= — a 1896 Apr. 29 70° 5,556 ——— Set ae June 11 13° 4,000 pee 80° 6,000 1897 SS Sas Sas May 25 66° 8,800 Ss = <= 1898 —= = sees May 10 62° 38,400 June 28 78° 800 Go Bi 70° 1,000 > Year Date Temp. No. Date Temp. No. Date Temp. No. 1894 === —= Aug. 15 84° it SB3i7/ == | SS 1895 July 18 80° 19,080 Aug. 21 82° 10,683 Sept. 12 79° 2,336 1896 July 6 80° 2,800 Aug. 8 86° 7,200 1897 July 21 81° 49 ,600 Aug. 17 79° 9,600 Sept. 7 80° 70,000 1897 Oct: 5 712 8,000 == = == 1898 July 26 g9° | 28,000 | Aug. 30 | 83° 6,400 | Sept. 27 73° 14,400 This is an exceedingly variable species. It varies in the relative length of the three long setz, in their spinosity, and in the location of the posterior one. Many of the individuals in our waters resemble the form described by Plate (’85) as T. terminalis. The long-spined form described by Zacharias (’94) as var. lomnetica is also abundant. It is doubtful if either form is worthy even of varietal distinction. This species has been reported only from Lake Erie and the Illinois River in this country, and seems to be rare in the former. Weber (’98) finds it abundant in the plankton of Lake Leman; Burckhardt (’00 and ’00a) reports it as wide-spread and almost perennial in Swiss lakes, but with its maximum in December— February, and slight development during warmer months. Borge (’00) finds it to be one of the common rotifers in the summer plank- ton in Sweden; Marsson (’00) reports its perennial seasonal range in several German waters, with greater numbers during the warmer. season. Apstein (’96) gives it a perennial distribution in Lake Plon, with larger numbers in June-November, and maximum in June-July or August. According to Seligo (’00) the species is per- 219 ennial in lakes near Danzig, rivaling Polyarthra in abundance, and exhibiting maxima in the warmer months from April to October. It is also a member of the potamoplankton of European streams. Skorikow (’97) finds it in summer months in the Udy, and Zimmer (°99) reports it as present in small numbers and irregularly in the Oder from April to November. Schorler (’00) finds it in the Elbe in May—October with maxima in May and September, and Lauter- born (’98a) includes it in his list of perennial rotifers in the plankton of the Rhine. It has two sexual periods, the first in March—May and the second in July—October, and he suggests the probability of a polycyclic habit in some waters. Trochosphera solstitialis Thorpe was found June 27, July 2, and August 15,in 1896; in 1897,0on May 25 and July 14-30. Free winter eggs were taken August 15, 1896. All occurrences were above 66°. These records were all from plankton taken in mid-channel of the main stream. Trochosphera was found in greatest abundance at the outlet of Flag Lake (Pt. I., Pl. II.) in July, reaching 9,664 per m.* at 72°. It was also found in August in the weedy backwaters of Dogfish Lake. Both of these backwaters connect with the river (Pt. I., Pl. II.) below the point at which our collections were made. It was either introduced from some similar backwater higher up the stream than our plankton station, or developed in the river itself. SCIRTOPODA. This order is represented in the plankton by a single species, whose discussion will suffice for the order. Pedalion mirum Huds. Average number, 4,524. This is a summer planktont of somewhat definite temperature limits. The following table combined with the data in Table I. will suffice to characterize its seasonal fluctuations. Its limitation to temperatures above 60°, indeed almost 70°, is apparent. There are in all but two records below 60°, and but four below 70°. It is a typical midsummer planktont, with several recurrent pulses during the period of maximum temperatures. The location of these pulses with reference to those of the chlorophyll-bearing organisms is significant. As shown in Table I., they follow immediately, or coincide with, those of the synthetic organisms. For example, the apices of the pulses of Mastigophora, 220 First record First maximum Year Date Temp. Date Temp. No. DS OF eva ntasins let muemaemio eee mene = === June 29 83° 2,592 TS OD) Sees yy nae mene Macey crete = == July 6 80° 330,932 USO .G fede raiCas astern oe May 25 70° July 28 80° 20,000 BO i cease ie Reta, Waadeeee Lert June 28 (oe July 21 84° 80 , 000 TSO Se rant kel eis teenie Janes 24 (ithe July 26 89° 99 ,600 Second maximum Last record Year Date Temp. No. Date Temp. ALCO Oe Pec Sue toner rranar Saperecom Ar Sea = —— — ——— | Sept. 17 7-8 UB OOP areas ers rue ene: Auge 20 Sie 3 00a | Oete 2 63° IW SIO) o ices at eres AR ete a peegen Etn cnt wiley Sale 77,600 | Sept. 16 qe TOV ee Ue eh claret me haa 2 Aug. 17 79° 79,200 | Sept. 14 73° SO Sis ices Lucia ene ner eae Aug. 16 LU? 22,400 | Nov. 1 45° Bacillariacee, and Chlorophycee in the period in question in 1898 are (Pl. II.) July 19, August 9, August 30, and September 27. The apices of the Pedalion pulses are July 26, August 16, and September 27, the last coinciding with the pulse of chlorophyll-bearing organ- isms. In 1897, the intercalation of the two pulses is apparent, and in 1896, two out of three pulses are intercalated and a third is coincident. As will be seen in Table.J., these pulses of 1898 are approximately coincident in many cases with those of other roti- fers—Syncheta, Polyarthra, Triarthra, and Brachionus. The sig- nificance of this intercalation lies probably in the food relations of the two groups of organisms. Females with a single egg attached to the body have been noted at the times of the maxima of the pulses, or immediately thereafter, a 221 in five instances. On the pulse of July 26, 1898, a female with four male eggs was found. This species was not reported by Apstein (’96) from the lakes of Holstein, but was found by Lauterborn (’98a) in the Rhine and its backwaters. Here also it was a summer form, appearing about the middle of June, with a maximum in August or September and disappearing late in October, conditions of distribution much re- sembling those in the [llinois. It is regarded, along with other summer forms, as monocyclic. The appearance in our waters of male eggs July 26, at the height of the first pulse, leads to the in- ference that there may be several cycles; for example, three in 1898, with the recurrent pulses, in a single summer season. Weber (798) gives it as a summer rotifer in Switzerland, and Skorikow (’97) finds it in July-September in the Udy River,in Russia; but it is not reported from the Oder by Zimmer (’99), nor from the Elbe by Schorler (’00). Kellicott ((97) finds it in Lake Erie in small numbers in the summer. In addition to the species of rotifers noticed above, Hempel (’99) has reported the following in the Illinois River or its backwaters: Floscularia ornata Ehrbg., Lammias ceratophyllt Schrank, Cephalost- phon limmias Ehrbg., Gecistes antermedius Davis, O. mucicola Kell., Pedetes saltator Gosse, Furcularia forficula Ehrbg., F. longiseta Ehrbg., Eosphora aurita Ehrbg., Diglena grandis Ehrbg., D. catellina Ehrbg., D. biraphis Gosse, Celopus tenutor Gosse, Scaridium longi- caudum Ehrbg., Distyla gissensis Eckstein, D. ohioensts Herrick, D. stokest Pell, and D. hornemanni Ehrbg. Gras PROD RUC HA. Chetonotus sp. occurred singly in the plankton August 29, 1896, July 30, 1897, and February 15, 1898, with a temperature range of ge.5 to 84°. ENTOMOSTRACA. Average number, 47,042. In 1897, a more stable year, 91,050; in 1896, a year of disturbed hydrograph, 50,158; in 1895, in more stable conditions, 148,348. The Entomostraca appear in every collec- tion at all seasons of the year. The decline to the winter mini- PHEAS mum occurs in November—December. Numbers are at a minimum generally less than 5,000 per m.*) in midwinter (January—February) ; rise in March to about 25,000 per m.*; and attain the maximum for the year in a vernal pulse of 200,000 to 1,500,000 in April—May. Following this, there is frequently a second pulse of large proportions in June, which in 1898 exceeds (Table I.) that of May. During the remainder of the year there is usually a series of recurrent pulses, of declining amplitude in 1896 and 1898, but rising to unusual heights (618,750 on September 9) in the stable conditions of 1897. In the main the pulses of Entomostraca coincide with or approximate to the location of those of the other organisms of the plankton, and often show correlations in amplitude. BRANCHIOPODA. Eubranchipus serratus Forbes. Young branchiopod larve questionably referred to this species appeared in the plankton in January—March, 1899, in small numbers at minimum tempera- tures. CLADOCERA. Average number, 6,068 per m.*? In 1897 they were more abun- dant, averaging 17,863 per m.* in the more stable conditions of that year. In 1896,a year of recurrent floods, numbers fell to 7,719, while in 1895, a year of low water in spring, when many of the Cladocera attain their maximum, the greatest average, 31,937, was recorded. The phenomenal number of 443,716 per m.* appeared on June 19 in the stable low water (1.80 ft.) then prevailing. In 1894, another year of low levels, the annual average was also large (23,952), though probably enhanced by the fact that collections were not made in flood waters in this year. The Cladocera appear in all but 10 of the 182 collections enu- merated, the ten exceptions falling in November (1), January (2), February (6), and April (1), and usually in flood waters or, as in 1895,in stagnation conditions under the ice. Although the Cladocera occur in all months of the year, they nevertheless, as a group, exhibit decided temperature adaptations, as appears from the fact that all records in excess of 4,000 per m.* fall between May 1 and September 1 with but 6 exceptions,—4 in the phenomenally i 223 early spring of 1896, and 2 in the delayed high temperature of October, 1897. The minimum records (less than 500 per m.*) are found during minimum temperatures. The numbers increase slightly (generally less than 2,000) as temperatures rise in March—April, rise abruptly, — as they approach or pass 70°, to a vernal maximum in May—June, and decline during midsummer excepting when unusual pulses of Moina or Diaphanosoma raise the level of the pulse maxima above 25,000. This decline continues in channel plankton through the autumn until the low level of approximately 2,000 per m.*, at the most, is again attained in October, and falls irregularly to 500, or less, aS minimum winter temperatures arrive in:'December. Ex- ceptions appear in 1897, when a well-defined autumnal pulse of large amplitude (193,500) is found on September 14, and is followed by others of declining amplitudes (137,600, October 5; 5,520, No- vember 15; 4,240, December 14) during stable autumnal conditions. All of the records above 4,000 per m.’, with one exception, are found at temperatures above 45°, and all in excess of 8,000, with 4 exceptions, after the vernal rise in temperature passes 70° in April— May, and before the autumnal decline reaches this point in Septem- ber. The Cladocera are thus planktonts of the warmer channel- waters. The relation which hydrographic conditions bear to the seasonal occurrences of Cladocera is apparent in the yearly averages above quoted, and appears still more clearly in a comparison of the cladoceran population and movement in river levels in July— December, 1897 and 1898, as given below. 7 = July August | Sept. Oct. Nov. Dec. Average No. | | | Cladocera 1897 |1898) 1897 1898 1897 |1898| 1897 |1898]1897|1898/1897/1898 per m.3 | | | 12720)3050 139603756 706751700 40350 1615/2532) 6201945 236 Total movement | | | | in river levels, See i esl) PAA 7.3) 76.6 92.) O26 |3.9 ARON a(8)\| Odensh|) 74 4! | | in ft. 224 Hydrographic changes affect the Cladocera by increasing the amount of silt and flocculent debris in suspension, which, by ad- herence to the swimming antenne and flotation processes of the animal, tend to impede its movements and sink it to the bottom, where it is removed from its normal feeding area and readily becomes the prey of the larger organisms of the bottom fauna. Barren flood waters also tend to displace and wash away in the increased current the Cladocera which have developed in the stream, and to afford both less food and less time for their further development. The occurrences of the total Cladocera fall into the type of recurrent pulses, though with slightly less distinctness than in the case of individual species of the group. Such pulses can be traced in all seasons in which records were made at short intervals, and suggestions of their occurrence appear in the less frequent records of other seasons. Thus in July-December, 1897, (Pl. IV.), there are 6 well-defined pulses culminating at intervals of 3(1), 4(2), 5(1), and 6(1) weeks. In 1898 (Table I.) the pulses are less regular in the flood waters of the disturbed year. In 1896, when records were frequent, we can trace pulses in March, May, June, July, August, and September. The character of these pulses is well illustrated in the vernal pulse of 1898 (Table I. and Pl. IV.), culminating June 7 at 136,000. The species which share in this pulse are Alona affints, A. costata, A. quadrangularis, Bosmina longirostris*, Ceriodaphnia scitula*, Chydorus sphericus*, Daphnia hyalina*, D. cucullata*, Diaphanosoma brachyurum, Leptodora hyalina, Macrothrix laticornts, Moina micrura, Pleuroxus denticulatus, Scapholeberts mucronata, and Simocephalus serrulatus. Of these, only the five marked by the asterisk occur in numbers sufficient by our methods to delineate a pulse. The other species are accordingly of little consequence in modifying the form or location of the pulse. The June volumetric pulse (Part I., Pl. XII.) culminates June 14 at 6.99 cm.* per Giee though the record for June 7 is also high (5.28). The cladoceran pulse culminates June 7 at 136,000. On this same day four of the dominant species also reach their culmination, viz.: Bosmina longtrostris (62,800), Cericdaphnia scitula (55,800), Daphnia cucul- lata (3,400), and D. hyalina (11,600), the remaining 2,400 being contributed by other species. Chydorus sphericus, which appears this spring only in small numbers, attains its maximum (7,880) on May 24, two weeks earlier, though the record for May 31 is also high 225 (5,040), indicating a probable maximum between these dates. In other seasons, for example in 1896 and 1897, the maxima of this species coincide generally with those of other Cladocera, so that this divergence seems to be anomalous. An inspection of the table of records for 1898 gives a remarkably uniform and coincident rise and decline of the pulses of the several species which constitute this characteristic vernal pulse. No effort has been made by me to determine the total cladoceran fauna of the Illinois River. Only those species are here given which have appeared in our plankton enumeration. A number of others are known to occur in the littoral fauna, and a few scattering indi- viduals found in the plankton were not identified. , Of the 25 forms here listed, only 10—named in the sequence of their relative numbers as shown in grand totals—may be regarded as typical planktonts, autolimnetic in channel plankton, viz.: Moina micrura, Bosmina longirostris, Daphma cucullata and vars. apicata and kahlbergiensis, D. hyalina, Certodaphnia scitula, Chydorus sphericus, Diaphanosoma brachyurum, and Leptodora hyalina. Of the ten, the last named and the varieties of D. cucullata appear to be of little quantitative importance in the channel plankton, though it may be that our methods of collection fail adequately to represent Leptodora. Of the remaining 15 species, Alona affints, Ceriodaphnia reticulata and C. rotunda, Scapholeberis mucronata, and the two species of Simocephalus are the only adventitious Cladocera of quantitative importance, and this only to a relatively small extent. DISCUSSION OF SPECIES OF CLADOCERA. Alona affinis Leydig.—Average number, 36. This species has a well-defined seasonal distribution. It appears in autumn in the last of October, as temperatures approach 40°, and remains until the end of June, when the summer maximum of 80° is re-established. The numbers are too small (Table I.) and irregular to define its seasonal fluctuations, though there are suggestions in the records of late autumnal and of vernal pulses. Egg-bearing females were recorded in January—February at minimum temperatures. No close dependence on hydrographic fluctuations is apparent to account for their occurrence in the plankton. Alona costata Sars.—Average number, 11. Only a few scattered occurrences of small numbers. Earliest autumnal record, Novem- ber 22, at 40°; latest vernal, May 24, at 73°. 226 Alona quadrangularts O. F. Mill—Average number, 5. A few scattered occurrences in March—May. Alona spp.—It is probable that some of the foregoing species of Alona are here included. There are 16 occurrences, scattered through all months but January, April, and November, with no large numbers and no marked seasonal distribution. Bosmina longirostris O. F. Miull—Average number, 2,441, of which 1,527 are adult females without large embryos, 390 with them, and 524 immature. I include in this species B. cornuta Jurine, for Jam unable to find any constant line of demarcation between these forms. The longirostris form 1s the dominant one in the channel plankton, the cornuta form being relatively rare. Bosmina is a perennial planktont in our channel plankton, but » occurs in small numbers only in October—May, no record in this period with the exception of that of October 5, 1897 (20,400), at 71°, exceeding 5,000 per m.*, and most of them falling below 2,000. The records in November—March, with the exception of November— December, 1897, all fall below 1,000 per m.* In like manner the percentage of collections containing Bosmina in December—April is lower than-that in the summer, the percentages being 64, 16, 26, 47, and 55 per cent. respectively for these colder months, and averaging - 82 per cent. for the rest of the year. The percentage of occurrences in October-November remains high (82 and 81 per cent.), though the numbers per m.° fall off greatly. The usual seasonal distribution is as follows: In January—March the occurrences are scattered and irregular and the numbers very small—less than 500 per m.2 Toward the close of April the vernal increase makes its appearance, continues slowly through May, rarely attaining more than 5,000 per m.%, and at the end of this month or early in June reaches the maximum development of the year in a vernal pulse of 40,320 (1896) or 62,800 (1898) per m.* From this summit there is an abrupt descent in a period of exhaustion to a level of less than 2,000 per m.* in the last fortnight of June. During the remainder of the year there appears a series of recurrent pulses — of less magnitude, exceeding 10,000 per m.* in but three instances. These follow at intervals of four to six weeks. In July-September the amplitude of these pulses exceeds in all cases 5,000 per m.* In ~ October (with the exception of 1897, when temperatures were un- ~ 227 usually high), they decline in amplitude, and in November—Decem- ber often fail to appear in the small numbers recorded. In 1894, records are too scanty to be of significance. In 1895 there are three well-defined pulses, and traces of a fourth in August-Novem- ber. In 1896 there are five in May—September. In 1897 there are six in July-December, data during the remainder of the year being insufficient to define the pulses. In 1898 the vernal pulse in June and a feeble one in October are the only ones which appear. The pulses of Bosmina are best defined in the stable low water of the last six months of 1897. During that period they closely approxi- mate in location of maxima and minima the quantitative pulses and those of the chlorophyll-bearing organisms and of the rotifers. (Compare on this point the plates for 1897 in Part I.—Kofoid, ’03— and Pl. IIJ.andIV.). The slopes of the pulses indicate that Bosmina is capable of very rapid multiplication; and their coincidence with _ other pulses just noted, taken in conjunction with the fact that males and ephippial eggs appear but rarely, suggests that these pulses of Bosmina are immediately dependent, in large part, upon fluctuations in the food supply for their origin and for the varying courses which they run. The relations of Bosmina to temperature appear in the facts that all pulses exceeding 5,000 per m.* in amplitude occur at tem- peratures above 70°, that the vernal rise does not proceed with any rapidity until this temperature is attained, and that the depressing effect of the autumnal decline below 70° is at once apparent in the reduced numbers per m.* No constant relation between the pulses of Bosmina and the midsummer heat pulses—such as appears in the records of Diaphanosoma—can be traced in the occurrences of Bosmina. An inspection of the accompanying table, in which the mean monthly Bosmina population per m.* of channel water in July—De- cember, 1897 and 1898, is given, and also the total + and — move- ment in river levels for these months in each year, will suggest an intimate connection between stability of hydrographic conditions and the increase of Bosmina. In 1897 the total movement for these months is from five sevenths to one tenth of that in 1898, and in every instance the Bosmina population is also greater by from 7.5 to nearly 400-fold in 1897, the more stable year. The means of the six months are 2.03 ft. and a population of 3,691 in 1897 to 5.3 ft. and (16) 228 BosMINA AND HyDROGRAPHIC FLUCTUATIONS.* July August September bite Total Bosmin Total Bosmina Total Bosmina movement, Yes a movement, roa? movement, | or Mae in feet Der ae in feet RE ; in feet P ’ —3.9 —2.6 — .2 1897 5 6,213 2.6 3,973 6 3) O22 +1.1 +0 pees —6.9 —3.3 —2.6 1898 7 140 Hoff 10 6 | 15 | + 1 +4.4 +3.4 | October November December Mean total” Total Total Bosmina Bosmina Bosmina movement, a movement, 3 movement, ane in feet Bei: in feet Pee in feet Pp — 1 — .7 — .6 1897 6 Dre W is) DD 1,680 il 1,585 + .5 +1.5 ae) —1.1 — .6 —2.8 1898 | 3.9 780 32 32 3.8 60 +2.8 +2.6 +1.0 * + = rising levels; — = falling levels. 173 Bosmina in 1898. It is also true that months in which the disparity in stability is greatest are those in which the Bosmina ratios are greatest, and vice versa. It seems very probable that the increased current, the lessened time for breeding, and the greater burden of silt in flood conditions, especially rising waters, do not conduce to the rapid increase of Bosmina in channel plankton. The effect of the high temperatures of the late autumn of 1897 is apparent in the amplitude of the October, November, and De- cember pulses (20,400, 3,440, and 3,440, respectively), which exceed those of all other years at this season. Temperature thus plays— perhaps by virtue of its relation to the food supply—an important 229 part in the seasonal delimitation of the amplitude of Bosmina pulses. The Bosmina population in the plankton consists largely of parthenogenetic females. Males and females with ephippial eggs, were recorded only in October-December, 1897, and then only in small numbers and isolated occurrences. Females with eggs or embryos and the free young were found at all seasons of the year and at all temperatures, but most abundantly at the time of the pulses. Parasitized or fungused individuals are also found occasionally at these seasons of greatest numbers, and the high mortality following a pulse is evidenced by the large number of dead occurring in the plankton. The proportions of females, females with eggs or em- bryos, young, and dead during the May—June pulse of 1898, may be traced in the following records. BOsMINA PER M.3, May—JuNE, 1898. Date Females Eee Young Total living Dead A\j ory AO oie ere 800 @ O 800 0) BO £3 sis e's 1,600 400 800 2,800 0) mame Olrscigie : 1,600 1,000 1,000 3,600 400 “Or 1,300 1,100 1,100 3,500 100 a ALI res « ss\Sa 3,280 1,400 1,240 5,920 920 “Gee BIS) 4 WAG) 2 , 000 , ©, chee 33,920 1,280 {Cie 57 eeoeete 38, 800 9,200 14,800 62,800 9,200 0 oe 2,200 3,000 800 6,000 1,400 OY Ee ra ae 1,000 500 0) 1,500 100 MNP Osa sees ss 300 200 200 700 100 Bosmina longirostris has been frequently reported in the plankton of European lakes. Apstein (’96) finds it perennial in Plénersee with larger numbers in June—September and a maximum in July. No pulse-like recurrence is noted, parthenogenesis prevails, and males and ephippia are rare. His results, save in the matter of pulses, are thus in general accord with ours. Stingelin (’97) notes 230 great seasonal polymorphism in B. cornuta near Basel. Zacharias (97a and ’98b) records it in the plankton of German carp ponds. Stenroos (’97 and’98) finds it in waters of Finland and Karelia, where the cornuta type is littoral, and a limnetic form, distinguished by him as forma vernalts, is abundant in the plankton in May. Scour- field (°98) finds it common in the waters of Epping Forest, where it is perennial, males and ephippia appearing only in September— November. According to Scott (’99) it appears at various seasons in the lochs of Scotland in both the littoral and limnetic fauna. Burckhardt (’00a) gives an extensive revision of the genus Bosmina, and includes in the B. longirostris group nine other so-called species, among which are 8. cornuta Jur. The species is “ pelagic or hemi- pelagic” in various Swiss lakes, though apparently not in num- bers. The genus is there represented in the plankton’ prime pally by the B. coregont group. Amberg (’00) lists it from Katzen- see, near Zurich, as a perennial planktont with large numbers in May, August, and February, but gives no statistical data. Fuhr- mann (’00) finds Bosmina perennial in Neuenburgersee, and B. longirostris with a’maximum in May. Marsson (’00) finds B. “longtrostris-cornuta”’ in lakes about Berlin throughout the year, with larger numbers in some lakes during the warmer months and in others in November—December. In Barlewitzersee, near Danzig, Seligo (’00) reports 6. cornuta-as perennial, with maxima in June and in October-November, the latter being the greater. Larger numbers appear in summer than in winter. Cohn (’03), in waters near K6nigsberg, finds 6. longirostris only sparingly present, appearing in May—September with a maximum in July. In European streams, also, B. longirostris is widely distributed. Lauterborn (’94) finds it abundant in the winter fauna of the Rhine. He also states that it is not acyclic in the backwaters, where he has found in three successive years both males and ephippia in May—June and againin November. ‘There is thus a suggestion of a vernal and an autumnal pulse in these waters. Zimmer (’99) finds it through- out the whole year in the Oder. Schorler (00) reports it from the Elbe at Dresden in May—October, with larger numbers in May—June and September, while Fri¢é and Vavra (’01) find it in the same stream near Podiebrad. They state that B. cornuta is found in great numbers in 1 m.—surface in summer months, and B. longiros- iris sparingly in the littoral fauna. Steuer (’01) finds B.‘‘longirostris- 251 cornuta’’ in the backwaters of the Danube at Vienna in April-January. It exhibits a distinct seasonal polymorphism, with a large winter form and a smaller summer one. Data as to relative numbers during the year are not given. Skorikow (’02), in reviewing the investigations on the plankton of Russian waters, reports B. cornuta from the summer plankton of several streams, but expresses doubts as to whether “sie als autopotamische Planktonorganismen anzu- sehen sind oder nicht.’’ Meissner (’03) finds 4. cornuta generally in the Volga and its adjacent waters in the summer plankton, with largest numbers in August; and Zykoff (’03) reports it in small numbers from the same stream in May-July. It is not listed by Volk (’03) in the Elbe at Hamburg. B. longirostris occurs generally in American | waters, though apparently, often in small numbers. Thus Forbes (’82 and ’90) reports it in the plankton of Lake Michigan and Lake Superior, and it appears generally in lists of Cladocera from many widely separated smaller bodies of water in this country. Buirge (’95 and ’97) finds only a few Bosmina (species not stated) in Lake Mendota, but Marsh (’97) reports it (species not given) as perennial in Green Lake, with a maximum in November. His records have also a suggestion of an earlier pulse, in June, in which month there is a sadden rise from a previous minimum. This partial survey of the literature of the records of Bosmina in the plankton shows its wide distribution, suggests the probability of great variation, necessitating caution in the description of new Species in this genus, and indicates a wide diversity in its seasonal career even in waters with somewhat closely similar environmental conditions. Ceriodaphnia megops Sars was found singly but once—July 25, 1896, at 80°. Certodaphma reticulata Jurine was found in the plankton occa- sionally, and always in small numbers, in April-September. All occurrences appear at temperatures above 66°, and the earliest is on April 17, and the latest is September 21. Females with summer eggs were found in June—September. Ceriodaphmia rotunda Straus was recorded in 1894-1895, but not thereafter. Its identification is somewhat questionable, and if correct, this is apparently the first record of this species in North American waters, unless it should appear that C. alabamensts 292, Herrick or C. acanthinus Ross, which appear to resemble C. rotunda in some particulars, should be included here as forms or synonyms. The genus is sadly in need of revision. The forms referred to C. rotunda were found in August, 1894, and July-August, 1895, 16,536 per m.* appearing in the plankton on July 18 of the latter year. Certodaphma scitula Herrick.—Average number, 1,539. This species is closely related to the European C. quadrangula O. F. Mull, if, indeed, it is not identical with it. It is not impossible that it is the form imperfectly described by Say (718) as Daphma angulata. In the absence of a critical monograph of the genus I use the name applied in current American literature to this form. This is the most abundant species of the genus in our waters, outnumbering all others by over sixfold in the totals of our records. It is also one of the most important members of the Entomostraca in the channel plankton (total of all records, 156,119), being ex- ceeded in numbers only by Mota micrura (1,121,808), Bosmina longirostris (381,598), Daphmia cucullata (237,444), and D. hyalina (231,746). It occurs in all months of the year except January and February, but in larger numbers and in more of the collections in May—Septem- ber. Thus less than 6 per cent. (reduced to 2 per cent. 1f one;eem lection in the warm autumn of 1897 is omitted) of the individuals and only 20 of the 79 occurrences are found outside of the May— September period. Certodaphmia scitula is accordingly a summer planktont in channel waters. It is found in each year, though in varying numbers according to hydrographic and other conditions. Thus in 1898 the vernal pulse in June attains the unsurpassed amplitude of 55,800 per m.%, but declines in a fortnight and makes no recovery during the disturbed hydrographic conditions of ‘the summer. In 1897, on the other hand, our records were too meager to delineate fully the vernal pulse, and in the stable conditions of the summer and autumn the species continued in numbers whose totals exceed those of 1898 by 81-fold. Similarly in 1896 the more gradual changes in levels which attended the floods of that year permitted a considerable development of Certodaphma throughout the summer. Stable hydrographic conditions thus conduce to increase in Certodaphmia. The relations which I have shown to exist between bosmina and movement in river levels (see table on TAS, page 228) exist also in the case of Certodaphnia and in much the same form. The relation of temperature to Ceriodaphnia is evident in its seasonal distribution. It does not advance rapidly in its vernal increase until after the water warms to 70°, and drops suddenly in numbers when the autumnal decline passes this point. Moreover, seasonal variations in temperature are accompanied by correspond- ing shiftings of the pulses of Certodaphnia. Thus in 1898 the water did not reach 70° until about May 20, reaching 73° on May 24, and the vernal pulse of Certodaphnia began at once its rise to the maxi- mum of June 7. In 1896 spring was early, 72° being recorded in surface waters on April 24, and we find a vernal pulse rising to a maximum on May 8. So also in 1897, when high temperatures continued into the autumn, the decline passing 71° on October 5, instead of in the first half of September as in other years, we find the pulses of Ceriodaphnia extending into October with unusual amplitude, reaching 5,200 per m.* October 5, while the highest record in this month, or later, in other years was 280 perm.? Tem- perature rather than season is thus the dominant factor in the seasonal curve of occurrence of Ceriodaphnia. The form of this seasonal curve is typically that of a series of recurrent pulses of varying magnitude tending to reach the maxi- mum height in the vernal pulse of May—June, attaining often lower levels in July and rising again in August-September, and falling to a minimum, or even to disappearance, in October. These later pulses do not appear in the disturbed hydrographic conditions of 1898 (Table I.), but are clearly delineated in the summer records of other years, especially in the stable conditions of 1897, where well-defined pulses appear in July, August, September, and October, at intervals of approximately four weeks, culminating July 14, August 10, September 14, and October 5. Their maxima attain respectively 5,600, 2,720, 6,000, and 5,200 per m.*’, and the pulses are delimited in each case by minima of less than 500 per m.* They tend to coincide with those of other Entomostraca and to approach those of the Rotzfera. The Certodaphma population in channel waters is almost ex- clusively made up of parthenogenetic females. Males were not recorded at any time, though females with ephippial eggs appeared after the October pulse of 1897 and the vernal one of 1898. 234 Certodaphnia scitula appears but once in the records of European plankton, Scourfield (’98) finding it in the waters of Epping Forest. in September. The closely related C. quadrangula as well as the other species have been frequently recorded by European investi- gators both in the littoral and the limnetic fauna, but they appear to be less generally found there than the other dominant Cladocera of our waters. It does not appear in the plankton of our Great Lakes (Forbes 82 and ’90, Birge ’95), or in that of Lake Mendota (Birge ’95 and ’97), or Green Lake (Marsh ’97), but Herrick (’84) reports it as the most abundait species in Minnesota, and Fordyce (’00) finds it in Nebraska in shallow waters. A revision of the genus is needed before the seasonal distribution of the various species can be worked out ona basis that will make satisfactory discussions of the literature possible. Chydorus sphericus O. F. Mill.—Average number, 422, of which 26 are egg-bearing females, and 6 are immature, the remainder, 390, being females in which the ova were not prominent. The identification of species of Chydorus is attended by consider- able uncertainty. Comparison with named specimens from Europe supplied by Prof. G. O. Sars, leaves no doubt that C. sphericus is common in our waters, and it is apparently the dominant species. It is probable that several other species, as, for example, C. globosus Baird and C. celatus Schoedler, occur sparingly in our waters and have been included with C. sphericus:in my enumerations. The difficulties which attend the attempt to assign every individual to one of the several species of Chydorus can be appreciated only by one who makes the effort. The problem of their specific validity should be solved by a statistical analysis of the range of varia- tion. The seasonal distribution of Chydorus sphericus in channel waters is in its general outlines very characteristic and well defined. The following table, which gives the average number of Chydorus per m.* for each month of our collections, shows clearly that it is a vernal planktont, and that there is a slight tendency toward an autumnal pulse in September, when vernal temperatures return.- The number for November (222) would probably be considerably reduced if more than one collection had been taken in that month - in 1896. Omitting this year, the average for November falls to 2 ae ee JRF rom OPER DTD CE NL wi BO Ti Zo 78, and a secondary, hiemal rise becomes apparent in December. This December pulse of Chydorus is one of the elements in the upward movement of production in this month (see Part I.), and fuller data may serve to connect it fully with the September—October pulse, especially in more stable conditions. Both of these autumnal- hiemal movements have less than one tenth of the development that the vernal pulse exhibits. The number and percentage of occurrences also confirm the conclusions drawn from the numbers per m.* Percentages run higher in the spring, in March—May, and in September—October and in December, and lower in June-August, November, and January—February. Chydorus occurred in all March collections, and in only one third of the August collections. The analysis of the data in this table indicates the presence of Chydorus in the plankton practically throughout the whole year in the whole seasonal range in temperatures, with the larger develop- ments following shortly after the thermograph passes the yearly mean (57° average of monthly means of surface waters) 1n vernal rise and autumnal decline, the maximum development in April-May / SEASONAL DIsTRIBUTION OF CHYDORUS. AVERAGE NUMBER PER M.3 Year Jan. Feb. | March | April May | June 1 Oe ae ee ee aa a ——oo — 234 iL STDS nuh Gay ee eae a — 11 ——— 2,044 | ———— O SOME ae Sat Sac. Bees 304 167 1,682 0), Bi al 5,701 448 ie OPE OP ee een cig eine — 20 540 SAO) || S77 5 sh010) 900 OOM tae yc ers) a ale eres 160 O 256 300 3,364 356 LIS SIONS STACCRs CRC RCR RCE RE RCRE 36 65 193 —<$———— | ———_ a PMMEEACE.. tslle so bs. 167 5S) | 668 Be 235) [als 955 388 No. of occurrences...... 9 6 15 9 9 10 Percentage of occur- ETI CES ie ey sore Sess 75 40 100 82 90 M2. 236 SEASONAL DISTRIBUTION OF CHYDORUS. AVERAGE NUMBER PER M.3—continued. Year July Aug. Sept. Oct. Nov. Dec. 1S Are rene Seotoed ap adaltena ee ote 95 6) 461 100 16 56 1 BOS SP We nee ome ne Te eanes 91 103 164 38 203 448 1S DGi 5 ces Sst eteos eeu amon nehe 64 104 78 160 800 277 Ape te ty pateiey cls, astm Soa 213 40 407 650 64 115 VE OSA ne aie a es 50 0) 30 60 28 172 1S OO Bean at alee eee: == == —=— eS | —= AV eragen tas ncie eae 103 49 228 202 222 214 No. of occurrences..... 11 7 13 12 10 14 Percentage of occur- REN CES eases ee 61 33 81 71 63 82 occurring in average temperatures, for these months, of 60.5° and 68.3°, while the minor autumnal development appears in September— October at 74.2° and 57.6° respectively, and the December pulse, if indeed it be a separate and independent pulse, is at the low tempera- ture of 35.2°. The December movement may be simply the result of the more stable conditions which attend the appearance of the ice-sheet on the approach of winter. An analysis of the course of the seasonal distribution of Chydorus in channel waters, as given in Table I. and in statistics of other years, indicates the following seasonal regimen. In January—Feb- ruary, at minimum temperatures, the occurrences are irregular (75 and 40 per cent.) and the numbers small (average, 167 and 53 per m.*), while in March, with rising temperatures, occurrences are more numerous (100 per cent.) and numbers rise to 668 per m.* In April-May a high percentage of occurrences (82 and 90 per cent.) continues, and they mount rapidly to the maximum record of the year, which in our statistics varies from 4,088 in 1895 to 32,800 in 1897. This vernal pulse reaches its maximum in our records on April 29 in 1895, at 64°, and in 1896 on the same day, at 70°; on ew ae 237 May 25 in 1897, at 66.3°; and on May 24, in 1895, at 73°. From this maximum the pulse declines abruptly in a fortnight to a midsummer minimum during maximum temperatures, which continues until September. During this period the numbers are small, rarely rising above 400 per m.? (average, 388, 103, and 49), and the occurrences are also less numerous (72, 61, and 33 per cent.). With the decline of temperatures which begins in September the percentage of occur- rences mounts to 81, and the average per m.*'to 228, and remains near this level during the remainder of the year. An analysis of the full statistical data, of which the records for 1898 are fairly typical, confirms the conclusions drawn from these averages. Chydorus in channel waters is monocyclic, with a well- defined vernal pulse in March—June which includes 95 per cent. of the total annual Chydorus population. There are suggestions of an autumnal pulse, but the data are not sufficient to delimit it. There is no satisfactory evidence that there are recurrent cycles or pulses at briefer intervals during the year. The dominating effect of temperature as a regulating factor in delimiting the seasonal distribution of Chydorus is very evident. This, inaddition to its appearance in the annual curve of occurrences, is also exhibited most clearly in a comparison of the vernal pulses in the two years of fullest representation in our records, 1896 and 1898. The following table gives the data of dates, temperatures of surface waters, and numbers of Chydorus. From these facts it appears that the late spring of 1898 delayed the vernal pulse of Chydorus, and that the early spring of 1896 accelerated it in that year so that their apices (April 29 and May 24) are four weeks removed from each other in seasonal location. In both years the rapid rise in the pulse appears after 60° 1s passed, the culmination occurs at about 70°, and the decline, 7 temperatures above 70°. Egg-bearing females were more abundant during the rise of the pulse, and less numerous during its decline. Evidence of great mortality during the decline of the pulses is to be found in great increase in the relative numbers of empty carapaces. Thus, during the decline of the vernal pulse in 1896 there were on the day of culmination, April 29, 2,780 dead to 18,904 living, on May 1, 3,570 to 14,875, and on May 8, 1,578 to 6,706. From 14 to 24 per cent. of the Chydorus population had thus recently perished. Parasitized 238 1896 1898 Date | Tempera | tet | Date | lane. IVs ato 42° 256 Mar. 15 46° 440 eats 40.7° 610 SOD 51° 480 fae 6 Pete Be 48.1° 6,405 ECON er 495° 240 Apeel Ole mre 46 .4° 1, 666 Apr. 5 483° 200 Carel Tantei 66:32. |") Ars is LOSE SGe 200 BO ie WE | 15,900 PE ESS Soe 56° ir ORO aaaeaa 68° 18,904 96 ace Mee aaa 800 Miciyeusle eae 68. 8° 14,875 May: ee: 60° LN ase HE) TOS SF AO: See 62° 600 He Set rt 71.2° | 1,143 i Aaa 64° 3,300 wat Sue a (eee i 80 CoA D ARN 730 7,880 Se ews 70° 5,040 Junertor ee 79° 320 June 7 78° 600 sO b ca a 73° 320 of saan 82.3° 200 and fungused individuals were also noted in these periods of decline. Males were recorded in September, December, and February. Chydorus is not given as a constituent of the plankton of Nor- wegian lakes by Huitfeldt-Kaas (’98) or of Swiss lakes by Fuhrmann (00), Amberg (’00), or Burckhardt (’00 and ’00a). Its absence from these cooler waters stands in sharp contrast with its abundance in warm and shallow European lakes. It is reported as abundant in Chroococcacee-rich lakes of North Germany by Apstein (’96), where it is acyclic, with larger development in April—October, and maximum in August or in May-June. According to Weismann (°79) Chydorus in some waters is polycyclic. It is also reported by Zacharias (’97a and ’98b) from the pond fauna of Trachenberg and many other German localities, where it forms “ein notorisches 239 Mitglied des Teichplanktons.”’. He also lists it ('98b) from some German streams. Marsson (’00) found it in some waters near Berlin in April—August, noting a great abundance in one instance in May. Seligo (’00) gives a few statistical data indicating the occurrence of Chydorus in the plankton of Hintersee near Danzig in April- December, with a maximum in August and a secondary one in October. It was, however, sparingly present in adiacent waters. Cohn (’03) finds a like irregularity in its occurrence in waters near K6nigsberg. Stenroos (’97) finds it to be one of the most abundant Entomos- traca in the waters of northern Russia and (’98) a littoral and bottom species near Helsingfors. Scourfield (’98) finds it to be one of the most abundant Cladocera in the waters of Epping Forest, occurring from March to December, with maxima of sexual reproduction in April and November. Scott (’99) reports it as abundant in the littoral fauna of Scottish waters, but rare in tow-net collections in open water. It also occurs in the potamoplankton of European streams, Zacharias (’98b) listing it from a few minor streams, but without seasonal, statistical, or temperature data. It was not separately listed by Skorikow (’97) in the summer plankton of the Udy at Charkow, or by Lauterborn (’94) in the winter plankton of the Rhine. Zimmer (’99) found it from February to July in the Oder, and Schorler (’00) finds it abundant in the plankton of the Elbe in April. Steuer (’01) finds it at all seasons in the backwaters of the Danube at Vienna, and in the plankton from March to November “oft in gréssern Mengen,” but gives no statistics of its seasonal distribution. Frié and Vavra (’01) find it in the channel and backwaters of the Elbe near Podiebrad, but more abundant in the littoral fauna, though no quantitative or statistical data of its occurrence are given. Zykoff (’03) reports it as present in the plankton of the Volga at all times in small numbers, and suggests a predominance in May—July. Meissner (’03) also reports it for the Volga, but states that it is predominantly a member of the littoral fauna though present in the plankton of the stream in restricted numbers. No statistical data are given by him. Volk (’03) reports it in the Elbe at Hamburg, but without any details. This species is reported generally from American waters. Forbes (790) reports it in the summer plankton of Lakes Superior and 240 Michigamme in small numbers, and (’93) in that of the Alpine waters of Wyoming and Montana, where it is, however, more abundant in smaller pools. Birge (’94) finds it generally distributed in collec- tions, including plankton, in Lake St. Clair and (’97) a member of the plankton of Lake Mendota, where its abundance is dependent on the supply of Anabena. Its maximum—only a single well-defined one occurring in each year—was found in July—October. Birge regards it as an accidental member of the limnetic fauna, maintained there as long as suitable food is present. Its mode of occurrence does not, however, differ from that of typical plankton organisms, which would doubtless likewise disappear from the plankton if their food should be lacking. It is noteworthy in this connection that it was only sparingly present in the channel of the [Illinois in the midsummer—autumn plankton, when—as, for example, in 1897—Anabena and its allies were abundant. It seems not improbable that temperature even more than food is an important factor in controlling its seasonal and local distribution. It is unquestionably a member of the plankton in our waters, though also abundant here, as elsewhere, in the littoral fauna. In our locality in channel plankton it shows distinctly seasonal limitations which suggest the operation of tem- perature rather than food. Its occurrence in large numbers in Wisconsin lakes in midsummer and its absence in the Illinois at that time may also be correlated in part with the contrasted tem- perature conditions in the two localities. Its occurrence in our littoral fauna may also in part be due to the lower temperatures consequent upon spring-fed areas and the shade of aquatic vegeta- tion. Chydorus is one of those organisms capable of both the littoral and liamnetic habit under suitable conditions of food and temperature. In our waters, at least,—and, as it seems from the data of distribu- tion, elsewhere,—temperature, rather than food directly, appears to be the factor controlling the occurrence of Chydorus in the plankton. Daphnia cucullata G. O. Sars.—Average number, 181. In 1897, very much greater,—5,483 per m.? For the reasons given by Burckhardt (’00) I use Sars’s name cucullata rather than jardinez of Richard to designate those forms of the subgenus Hyalodaphnia in our plankton. In channel waters this species varies considerably, but not to the extent that it does en 241 where its numbers are greater. The forms known as apicata Kurz and kahlbergiensis Schoed. appear in small numbers in some years. This species appears in our collections in April-December only, with the exception of one occurrence in January and two in March. Its occurrences and numbers vary greatly in different years. In 1894—95 its numbers were small and occurrences scattering, it being most abundant in November—December. In 1896 there was a large vernal development in April—June, and a series of diminishing pulses in July-September. In 1897 no vernal development appeared in our scattered collections, but in the stable conditions of late summer and autumn occurred the largest development recorded in any year, with a maximum record of 72,760 per m.* on October 5. In 1898 there was a small vernal development (3,400) in May—June and a still smaller one (600) in October. A well-defined seasonal routine is thus not demonstrable from our data, though the fact that both the percentage of occurrences and the numbers are highest in May—June and September—October suggests a tendency toward vernal and autumnal pulses separated by a period of less develop- ment in midsummer and of autumnal decline followed by a period of almost complete extinction in midwinter. The statistics of the D. cucullata population in all years in which weekly collections were made, exhibit very clearly the phenomenon of recurrent pulses of 3 to 5 weeks’ duration, with maxima of varying amplitude and minima of less than 400 per m.* in all cases but those which mark the September pulse of 1897. There are in 1896 pulses culminating April 24 (2,544 per m.%), May 8 (11,965), June 11 (12,000), July 18 (1,040), August 8 (800), and September 16 (507). In 1897, vernal records are incomplete. Pulses appear July 14 (800), August 17 (1,680), September 14 (57,000), October 5 (72,760), and November 15 (2,040). These pulses coincide exactly or approxi- mately with those of the other Entomostraca which exhibit the same phenomenon, and approximate also those of the Rotifera. A typical pulse, that of October, 1897, is shown in the following table. It is a noticeable fact that the proportion of immature forms is often greater at and after the period of maximum development than at other times, as appears in the table. The relations of temperature to the development of D. cucullata in channel waters appear in the fact that all occurrences in excess of 242 Date Females fon ae Young Total ‘a aoe SISO 740) a emaraia ain co's bic 160 SAO) 640 1120 57 ST ee a 13020 4,000 12,800 24,320 52 Oct ais tose ewes 3,560 10,800 58,400 72,760 82 2 years hcteneh ste 1,600 7 600. 4 9729206 83 I iAGl6 eid 1esorO obo 560 840 4,440 5,840 76 600 per m.?are found after the temperatures pass 70°, with the'single exception of the decline of the October pulse and the rise of the November pulse to 2,040 per m.* at 47°, following the high tempera- tures in the late autumn and stable conditions of 1897. From the depression in numbers during the period of maximum heat 1n mid- summer and the occurrence of the major vernal and autumnal pulses before and after its reign it appears that the temperature optimum for D. cucullata in channel waters lies below this level, that is, below 80°. D. cucullata is evidently very easily affected by the changes in hydrographic conditions. Thus, in July-December, 1897 and 1898, the total movement in river levels was 12.4 and 31.4 ft., respectively, while the total cucullata population for these months was 186,420 and 1,140—164-fold greater in the more stable year. D. cucullata thus exhibits the maximum sensitiveness among the Entomostraca to these environmental factors. The D. cucullata population in the plankton consists almost entirely of parthenogenetic females and young. The immature stages form about 60 per cent. and the egg-bearing females 16 per cent. of the total individuals. Dead, parasitized,or fungused indi- viduals were found at times of the maxima or shortly thereafter, but never in very large numbers. Males were found once in December, 1896, and ephippial females also but once, on October 19, 1897, during the decline of the maximum pulse in our records. Daphnia cucullata var. apicata Kurz, in well-developed condi- tion, was found in relatively small numbers during the vernal pulses of 1895 and 1896 and the autumnal pulse of the former year. 243 Incipient stages of this variety appeared also at other times. Burck- hardt (’00a) does not even concede varietal standing to apicata, regarding it merely as a form of seasonal or local value. Its occur- rence in our plankton when reproduction and growth are most active suggests that it may have a growth value, and be in some way correlated with the factors involved in its cyclic production. Daphma cucullata var. kahlbergiensis Schoed. appears but once in our records—in the plankton of June 11, 1896. The D. cucullata group is a cosmopolitan constituent of the fresh-water plankton, appearing frequently in the records of Euro- pean plankton. Apstein (’96) finds it in lakes in northern Germany in April—-October with maximum numbers in July. The seasonal limits thus resemble those in the Illinois, but the maximum falls at the time of our midsummer decline. Temperatures in these German lakes (16.3° C.) do not, however, reach the high levels attained in our waters in midsummer. Stenroos (’98) records it in several varieties in the plankton of Nurmijarvi See, the helmeted varieties being found in midsummer. Zacharias records it from the plankton of German ponds. Scourfield (’98) finds it in small numbers in Epping Forest interruptedly in April-November, a season coinciding with that in the Illinois. Burckhardt (’00) finds it represented by five different “forms”’ in Mauensee in the June plankton. Marsson (’00) finds representatives of Hyalodaphnia (species not given) in the April-June plankton near Berlin. Am- berg (’00) states that this species appears in April, increasing to a maximum in July-August, and disappears again at the end of November, a seasonal course similar in limits but not in maximum to that in the Illinois. His data are too scattered to trace the course of production with completeness. Seligo (’00), in waters near Danzig, finds the species present in June—January, with maxima in June-July and October. In the period of maximum summer temperatures (16°-21° C.) the numbers decline as in this period in the Illinois. In Seligo’s infrequent (two to three weeks’ interval) data there are suggestions of minor recurrent pulses 1n other months. Cohn (’03) finds in Léwentin a Daphnia which he calls D. galeata with vars. kahlbergiensts and cederstrémi, and includes all three in his enumeration. His investigation covers the months of May— September, throughout which these forms appear, rising in a series of recurrent maxima on June 26, August 4,and September 2 and 29. (17) 244 Cohn seems not to have called attention to these clearly defined recurrent pulses. In European streams D. cucullata also forms an important part of the plankton. Lauterborn (’93) states that, with its varieties kahlbergiensis and cederstromu, it appears abundantly in the plank- ton of the Rhine in summer, but is not found init in winter. Zimmer (’99) states that D. kahlbergiensis was found constantly in the plank- ton of the Oder in July-September, and Schorler (’00) also finds it in the Elbe at Dresden in May—August, with larger numbers in June and August. Steuer (’01) reports it, in small numbers only, in August in the backwaters of the Danube at Vienna. Fri¢ and Vavra (’01) report D. kahlbergiensts as rare in the Elbe. Sowinski (’88) finds it in several varieties in plankton of the Dnieper and its tributaries, Rossinski (’92) finds it in the summer plankton of the Moskwa, and Zernow (’01) in the June-July plankton of the Schoschma and Wjatka. Meissner (’02 and ’03) finds it in several varieties in the May—August plankton of the Volga. D. cucullata in some of its various forms or varieties appears to be widely distributed in American waters. It was reported by _ Forbes (’82), as D. retrocurva, from the plankton of Lake Michigan, | and also (’90) from Lake Superior and adjacent waters. Burge (791 and ’94) also finds it abundantly in Wisconsin waters and in Lake St. Clair. Herrick (’84) and Ross (97) report it from Min- nesota and Iowa. Careful studies of its seasonal and vertical) distribution in Wisconsin waters have been made by Marsh (’97) in Green Lake, and by Birge (95 and 797) in Lake Mendota. In Green Lake D. kahlbergiensts is reduced to a minimum or even extinction in December—April, rises in a late vernal maximum in June-July, falls again to a lower level in August-September, and then rises to a second and sometimes higher autumnal pulse in October. In its main outlines this conforms to the seasonal course of the cucullata form in our channel plankton. Our vernal maxti- mum appears somewhat earlier, as a result probably of an earlier warming up of the water. According to Birge (’97) this species is more definitely periodic in its occurrence in Lake Mendota, being confined entirely to July-December. Here also the largest numbers are found in October, and the individuals gather in lower levels as temperatures decline. 245 Daphnia hyalina Leydig.—Average number, 417. In channel waters this species has appeared in but two years, in 1895 in April-July, attaining on June 19 a maximum of 166,208 per m.°, of which 150,626 were immature. The collections were too infrequent in these months to trace the course of this vernal pulse. D. hyalina did not reappear until the spring of 1898, on May 24, in a single vernal pulse culminating at 11,600 per m.* on June 7, and disappear- ing a fortnight later. Its occurrences with one exception were all at temperatures above 70°. There is no apparent cause for its absence in later months or in other years. Males and ephippial eggs were not found. Daphnia hyalina is an exceedingly variable species, and a large number of forms have been described which belong to the hyalina group. Burckhardt (’00), for example, recognizes 26 such forms as varieties of this cosmopolitan planktont. This variability and the difficulties attending the resulting synonymy cause any discus- sion of the species in other waters to be attended by much uncer- tainty. I shall therefore not attempt to distinguish in my dis- cussion between the various varieties included by Burckhardt in the hyalina group. In lakes of northern Germany, Apstein (’96) finds that D. hyalina is essentially a winter planktont with a seasonal range of September— July, and with maximum numbers in November—January. The maximum thus appears there at the time of complete extinction in our waters. Stenroos (’97) records it (as D. galeata) in the summer plankton of Karelia, Huitfeldt-Kaas (’98) finds it in Norwegian lakes in July and September in considerable numbers, and Scour- field’s careful studies (’98) of its seasonal occurrence in waters of Epping Forest reveal an interrupted distribution in April-Novem- ber. Scott (’99) finds it in numbers in Scottish lochs in the plankton examined at long intervals in March—January. Fuhrmann (’00) reports it as perennial in Neuenbergersee, with a maximum in June followed by a midsummer minimum. Burckhardt (’00a) finds great diversity in different Swiss lakes and in different years in the relative numbers present. His intervals of collection were too great to detect any pulse-like movement in the production, and 1t may be that the diversity is due in part to the incompleteness of his records. He concludes that D. hyalina is at a minimum in March—May, increases in numbers slowly (with a preponderance of young indi- 246 viduals) in May—October to a maximum in November—January, which is followed by a rapid decline (with preponderance of adults) to the minimum. His results agree with those of Apstein (796) in the main rather than with ours in the Lllinois. Seligo (’00) finds D. hyalina in Hintersee, though it is apparently absent from the adjacent Barlewitzersee. In the former lake it appears in May, rising to the year’s maximum early in June, continuing throughout the summer in diminished numbers, and disappearing in October. In his infrequent records there are suggestions of several recurrent minor pulses during the summer. Cohn (’03) reports D. galeata— regarded by Burckhardt (’00a) as a form of D. hyalina—from the region of K6nigsberg, but refers it rather to the cucullata group. I shall therefore consider his results only in connection with D. cucullata. D. hyalina appears but rarely in the records of European potamo- plankton. Steuer (’01) reports it, in small numbers only, in May from the backwaters of the Danube at Vienna. Fri¢ and Vavra (701) state that D. microcephala—regarded by Burckhardt (’00a) as a form of D. hyalina—is abundant in the plankton at a depth of O-1 m. in April-November in the Elbe and its backwaters at Podiebrad. It is also reported by Zykoff (’00 and ’03) in the late vernal (June—July) plankton of the Volga at Saratoff, and by Meissner (02 and ’03) in the same stream in May—June. The examination of the plankton of the Volga made by these authors is far less extensive than that made of the Illinois River plankton, but as far as it goes it indicates a similar distribution of D. hyalina in the two streams. Volk (’03) reports it from the Elbe at Hamburg without data. The species appears to be widely distributed in American waters, being reported, in some of its various varieties or synonyms, especially from lakes and ponds. Smith (’74) finds it in the plankton of Lake Superior, Forbes (’82) in that of Lake Michigan, and Birge (’94) in Lake St. Clair. It was also found in the Illinois by Forbes (’78) and in the backwaters of the Ohio River by Herrick (’84), who reports it also from Minnesota waters. Birge (’91) finds it in lakes about Madison, Wis., and Fordyce (’00) in deep pools in western Nebraska. The only investigation of its seasonal distribution in American waters is that of Birge (’95 and’97) in Lake Mendota, where it forms about 3 per cent. of all the Crustacea. It is perennial 247 in this lake but exhibits great differences in its seasonal course from year to year. The vernal development in May—June (the only one in our channel plankton) is relatively large in each year, but is sometimes exceeded by an autumnal one in October. A midsummer minimum sometimes appears between these pulses, and a winter minimum in December—April is always present. From the data here reviewed it seems probable that the very limited seasonal distribution and irregular annual recurrence of D. hyalina in our channel plankton is in a measure indicated in streams elsewhere, and may have its cause in the instability of the fluviatile environment as compared with the lacustrine, where the species evidently finds its environmental optimum. Diaphanosoma brachyurum (Liévin).—Average number, 479, of which 154 are females, 49 females with eggs, and 276 immature. This species in our waters is monocyclic, with sharply defined seasonal distribution. With the exception of two records of young individuals in March—April, 1895 (and the identification of these individuals is questionable), all our records of occurrence in 1894-1899 fall between May 25 and October 19, the first vernal records appearing at temperatures of 55.8° to 72.3°, and the last autumnal at 52.5° to 65°. The one pulse-in each year—except in 1894, when none was recorded—falls in a period of 3-6 weeks in July-September, the first record above 2,000 per m.* appearing July 26, and the latest (with one exception, 2,175 on September 27, 1895) on September 7. The pulse varies in duration in different years from 3 to 6 weeks, and attains a maximum on dates ranging from July 26 to August 31, and varying in amplitude from 8,580 to 19,602 per m.* An analysis of the distribution of 61 recorded occurrences in channel plankton shows that of these only 13, or 21 per cent., occur outside of July-September, and that the records outside of the seven weeks of the pulse include less than 12 per cent. of the total individuals. A comparison of the seasonal curve of distribution with the annual thermograph reveals the fact that the pulse occurs toward the close of the period of maximum summer heat, and in every case at a temperature of 78° or above, and that the decline of the pulse often begins with declining temperatures, and is always accom- plished during the autumnal decline. The effect of summer heat pulses upon the Diaphanosoma curve is strongly suggested by the 248 data of the appended table, which gives the statistics of temperature, river level, and Diaphanosoma population during the periods of maximum development in 1895-1898. All these data except those of Diaphanosoma are shown graphically in Part I., Plates [X.—XII. The data for Diaphanosoma are less complete than the others, since all of the collections were not counted. In 1895 the Diaphanosoma pulse culminates at 19,602 on August 21, following immediately upon a heat pulse which culminates August 15 at 85.3°. The decline of the pulse occurs with a decline of temperature to 72° on September 7. The declines; bothman Diaphanosoma and temperature, are hastened after September 3 by 1895 | 1896 Date | River | Temp. Deiph. | Date _ River Temp. || Dose | eee | anosoma | | Sac anosoma | | | | | | a ei ees a ee 40 ee ee) pet EA bev) nai) | \ 3 5 800 Sas ete /— | ——]} * 18) 2.50 | 79 400 ually 923°0| 5,20, 40 580 ADA 3) A 0) ee 120 ENDO.) S538. lua moeis DAO 28 6 AO nee 7,440 Atigesie /aed OL eiems 1,088 Aued 3/850. eons 160 1) Shall Mogan eer 938 || « 8 [8240 else 14,260 iE |) DeA@ee aog4ug 9,801 “45 | 7-40 | 82 2,240 e294 We OO Sia ees WOOOD aie 1° Ol wale gest Omen mayo 880 29 | 258% 180 7,950 AG ae > 7.3 600 fh ccs 2 ae as Ne fee 90 alu) BIN ere 440 Sept. 5) 5270 eral a 189 | Sept.16 | 4.10 | 73.5.1) MGs PR el). YS 1,053 | 39 (4 30: | see ae 80 20) 320 79 HOS | =< he Dy | 3 O3h ules 2475 |} 249 1897 1898 Date Pee Temp. | Daaph. | Date an Temp. Daaph- | anosoma = anosoma July 14 GesOl | 579 160 || July 12 7.00 78 60 ioee 21 | SAD) | esas 960 | eee 1S) 4.70 84 40 30 4.60 84 4,720 AS 2.90 89 8,580 Aug. 10 2530 80.8 7,600 LNG, 2eiO Uses 6,960 Ce li 4-90 79 | 7,120 S 9 Se ZORN eos: 360 * 94| 1.80 | 77.5 | BeeeO |) 1 Gai) 3.708 | 77 60 31 1.80 80 11,000 | ays) 4.20 82 1,020 —<—$_—_— — — ——— | SHO) 3.90 82.5 2920 Sept. 7 | 1.80 80 7,600 | Sept. 6 4.70 79 240 ae | 2.00 83 1,500 | eae walks) 4.20 62.5 1,800 moe 2 2.00 71 240 | me () 4.20 73 960 — —— — ——— gee Dif 4.90 13 400 the rise in river levels. Prior to that date hydrographic changes are. slight. With falling levels and higher temperatures after September 7 there is a slight recovery in Diaphanosoma—trom 189 per m.* on the 5th, to 1,053 on the 12th. In 1896 a well-defined heat pulse culminates August 10 at 86.5°; and Diaphanosoma,on August 8 at 14,260, with an abrupt depression from 7,440, on July 28, to 160, on August 3, in flood waters. The decline of this pulse from the maximum on the 8th to 440 on the 29th is attended by a uniform decline in temperatures from 86° to 74.3° in fairly stable hydrographic conditions, that is, declining river levels. In 1897 there are two well-defined summer heat pulses, one culminating August 3 at 89°, and the other September 14 at 83°, separated by a depression to 77.5° on August 24. The crest of the Diaphanosoma pulse likewise has two apices, the first culminating at 7,600 on August 10, followed, during the decline in temperatures, 250 by a fall to 5,120 on the 24th, and, in the rising temperatures which then ensue, by a recovery to a second maximum of 11,000 on the 31st. Diaphanosoma then declines though temperatures continue to rise. These fluctuations all take place in comparatively stable hydrographic conditions. There is a suggestion in the records of this year that rising temperatures in midsummer conditions tend to accelerate, and falling temperatures to depress, development of the Diaphanosoma pulse, and also that after the pulse has continued for some time (six weeks in this instance) rise in temperature ceases to be effective. The autumnal decline in Diaphanosoma may therefore not always of necessity be due tc temperature decline alone. In 1898 there are also two midsummer heat pulses, culminating on July 26 at 89°, and August 30 at 82.5°, separated by a depression which reaches 77° on August 16. The depression to 78.3° on August 2, with the consequent appearance of a third summit at 83° on August 9, is due mainly to the fact that the temperature was taken at 9:15 a. m., while all the others were in the late afternoon. The seasonal curve of Diaphanosoma shows likewise two apices, the first at 8,580 on July 26, and the second at 2,520 on August 30, separated by a depression to 60 per m.* on August 16, when temperatures are lowest. In this year the flood of the middle of August doubtless plays a large part in depressing alike the thermograph and the seasonal curve of Diaphanosoma, but in the light of the evidence from 1897 in stable hydrographic conditions the direct influence of temperature is also possible in this instance. Diaphanosoma is thus a late summer planktont which in develop- ment 1s very responsive to changes in temperature. It appears in the plankton in small numbers shortly after the establishment of summer temperatures in May—June, but does not begin its maximum development until maximum summer temperatures have existed for six to eight weeks, and is apparently incited to this by a summer heat pulse. Males were recorded on July 18 and August 1, and ephippial females on August 1 and September 5. Dead individuals were most numerous during or subsequent to the maximum of the pulse. This species is reported by Apstein (’96) in the plankton of Dobersdorfersee, where it is also monocyclic, first appearing in May, and attaining its maximum in September, when the males first appear. In contrast with conditions in our waters the maxima Zo appear ajter the period of maximum summer heat. Zacharias (’97a) reports it from German carp ponds in July, and Stenroos (’97) lists it as a littoral species in midsummer in northern Russia. Scott (’99) finds it rarely in lakes of Scotland in August, and then only in the plankton, though many shore collections were examined. Burck- hardt (’00) reports 1t from the smaller and shallower Swiss lakes in isolated records ranging from May to November, and regards its absence from the deeper lakes as due to the low temperatures which at all seasons would surround its winter eggs, which sink to the lower levels. In Vierwaldstattersee (’00a) he finds this species in the plankton only in September—November, and then more abundantly near shore than in the middle of the lake. In Alpnachersee the period of occurrence extends from June to November with a maxi- mum in July. Fuhrmann (’00) gives the seasonal distribution in Neuenburgersee as extending from May to November, with a maxi- mum in September. Marsson (’00) finds a seasonal distribution from July to October in small lakes near Berlin. Seligo (’00) finds in Hintersee, near Danzig, a seasonal distribution in 1898 extending from June 6 to October 18, with a maximum of 225,000—under 1 sq. m., depth, 24 m. (?)—on August 9. Frié and Vavra (’01) state that this species is very abundant in summer months in the plank- ton of the backwaters of the Elbe, especially in levels at depths of 0-1 meter. Cohn (’03), on the other hand, finds in waters near K6nigsberg that Diaphanosoma is present in greatest abundance in depths of 20-30 meters. It occurs in summer months, with large numbers in July-September and a maximum in August-September. It was not found in shallow waters. As a constituent of the potamoplankton Diaphanosoma has been reported by Schorler (’00) in the Elbe at Dresden as abundant in June-September. Steuer (’01) finds it in the backwaters of the Danube at Vienna in June—September, with a maximum in August, but never in great numbers. Meissner (’03) reports it sparingly from the Volga in July. In American waters Diaphanosoma is widely distributed. Forbes (90) found it abundant below surface levels in Lake Michigamme in August. Birge (’94) reports it in the plankton of western Lake Erie but not in that of Lake St. Clair in September. In Lake Mendota, Wis., he (’95 and ’97) has worked out its seasonal and vertical distribution with a fulness and care not equaled by any 252 European author previously quoted. Our results in Illinois waters are in striking confirmation of his conclusions. He finds the first scattering individuals in the plankton late in May, but numbers do not rise until late in July or early in August, increasing rapidly through August or even into September, then declining rapidly, and disappearing entirely before November 1. The active period is thus at a time when a considerable part of the lake is at or above 68°. In our waters these temperature limits are 78° or above, but the sea- — sonal distribution is almost identical with that in Lake Mendota. He finds it more abundant in the upper strata, 0-2 meters, than in the deeper ones—just the opposite of Cohn’s (’03) results. Marsh (97) has also determined its seasonal and vertical distribution in Green Lake, Wis., with considerable care. Occurrences from the last of October to the last of June are very few, and maximum numbers appear from the middle of August to the middle of Septem- ber, when surface waters have a temperature of 65°-80°. It occurs in all depths (0-40 m.), but 70 to 80 per cent. of the individuals were taken within 10to 15 m.of the surface, the upper 5 meters being more densely populated by night than by day and in September— October than in August. Diaphanosoma is a typical planktont, with strong antenne, and an active swimmer. Examination of the literature indicates its wide distribution in the plankton of lakes and streams, and its very marked seasonal limitation to seasons of higher temperature. It is thus, as Birge (’97) has stated, markedly stenothermous. The divergent conclusions concerning its limnetic habit and its vertical distribution will doubtless be found to rest in some cases upon insufficient data, and in others, upon its reactions to varying condi- tions of hght and temperature. Eurycercus lamellatus O. F. Mutll.—This species occurred spar- ingly and irregularly in the winter plankton at minimum tempera- tures from November 30 to March 28. It is evidently adventitious. Ilyocryptus spinijer Herrick.—Average number, 4. This species occurred sparingly and irregularly in the plankton during the warmer months. The earliest record was on July 23, and the latest October 11 at 65°. This species is evidently adventitious in the plankton. I have doubtfully referred our examples to Herrick’s species I. spinifer, for the reasons given by Herrick and Turner (’95), rather than to J. longiremis, to which Birge (’91) would refer our 200 American form described by Herrick as I. spinifer. A larger amount of material exhibiting a fuller range of variation may, however, serve to connect the two. Leptodora hyalina Lilljeborg.—Average number, 3. This species occurred in small numbers and somewhat irregularly in our collec- tions of channel plankton in summer months. Our earliest record was June 28; and the latest, August 30. It is our largest crustacean planktont and a fairly active swimmer, and was often taken in our tow-nets, which had a larger mouth and coarser mesh (No. 12) than our plankton net. I took this species in great numbers in the upper meter of water at midday in May—June in Lake Meredosia with a seine of No. 000 silk. It may be that it is less abundant in the channel than in the backwaters, and the small number in the plank- ton collections from the channel may also be accounted for in paft by the escape of Leptodora from the small orifice (10 cm.) of the plankton net, or to its negative rheotropism when stimulated by the currents of the plankton pump. Macrothrix laticornis Jurine was found in the plankton in May at 64°-73°, adventitious in flood waters. Mona micrura Kurz.—Average number, 261 per m2 In 1897 it was much more abundant, averaging 5,106 in the more stable conditions of that year. This is the most abundant of all our Cladocera, appearing in great numbers in periods of stable low water during maximum temperatures. It is exceedingly irregular in the extent of its devel- opment in different years, the average numbers per m.* in 1894-1898 being respectively 21,844, 22,842, 188, 5,106, and 261. After mak- ing allowances for the irregularity in the number and distribution of the collections in the several years, it still remains apparent that Mozina is very uneven in its distribution. The seasonal distribution of Mona in channel plankton is con- fined to July-September with the exception of 9 occurrences in small numbers in the last days of June and the early part of October. The earliest record is June 19, in 1895, when the very large number of 329,448 per m.* were found,—a degree of development which implies a previous period of multiplication. The first records in subsequent years were all later than this date in June or early in July. After several recurrent pulses, each of 3 to 5 weeks’ duration, the numbers decline to a very low level, and the species disappears 254 from the plankton in September—October. In 1898 (Table I.) the last record was made October 11—the latest in any year with the exception of an isolated record October 26, 1897. Mota micrura is thus distinctly a summer planktont. It appears in the plankton only after maximum summer tem- peratures of approximately 80° have been reached, and decreases rapidly as soon as the autumnal decline passes this point, and soon thereafter vanishes from the plankton. Its optimum temperature in channel waters is thus near 80°. The relation which hydrographic conditions bear to the ap- pearance of Moina in channel plankton appears upon a comparison of the Moina population and the movement in river levels in differ- ent years, as shown in the following table. Moina AND HyDROGRAPHIC CHANGES. June July August September October S09 = So = Se = Ss q Se £ ver| =e |. 2 |. "a Ju | =e |b oe | e) fe} {e) ° ° Zo cS Zo g Zo = Zo g Zo S oe ie Saga se aaa fale wo | »” | 3 a ° a ° a ° a ° e ° ee 0 0 0 ) 0 600 1,800 Rae Dic on. 0 0 0 0 0 0 800 >) ee 0 ) G 0 0 600 200 iin (0) 100 ) 0 0 (0) 200 OU eae 0 100) (0) 0 0 0 0 = I ae ee Oo. 0) (0) 0 0 400 400 07) ee ‘ 0 0 0 0/1,800,000} 3,200 1,600 Meaty) 1332 esis sss 0| 3,200 0 0|7,200,000| 3,200 0 “ee ) 0 0} 57,600,000!7,200,000| 6,400 4,800 313) ee 1,800,000 0 (0) 0 0} 4,800 5,600 “oy ae 0 0 ) 0 0 600 1,600 SNe See 0 (0) 0 5,400,000 0 1,000 600 ner G7 s.. 2.0.2 0 (0) 0 0 0} 3,200 12,800 1 ee 0 0 1,800,000 0 0| 32,000 39,400 o" 0 0 0 0 0 800 56,000 ae 0 0 3,600,000 (0) 0| 6,400 55,200 Tike Sees 0 0 0 ) 0| 3,600 44,800 A eee 1,800,000 0 0 0 0 1,200 49 ,200 nL Oe 1 s) 10,800,000 0 0} 61,200,000 0| 4,000 136,000 BED ON 2 ho.s.c 5,400,000 0 9,000,000 1,800,000/1,800,000} 4,000 247 ,600 AO DS Se 3, 3,600,000 0 ) 9,000,000 0| 4,800 295,200 Renee: 5,400,000 | 0} 10,800,000} 158,400,000 0| 2,800 145,600 pelo cs. 5,400,000 ) 3,600,000} 18,000,000 0 1,600 66,400 ROSE can n' « 10,800,000 ) 900,000} 14,400,000 0 5,600 194,400 mens Oars pec 21,600,000 0 1,800,000} 21,600,000/7,200,000| 8,000 326,400 SepiaO. 2... 10,800,000 0 0 0 0} 12,000 177,600 peTS 2 it. 7,200,000 0 1,800,000 7,200,000 0 500 42,000 0 a ae 7,200,000 0 0 0 0| 8,500 76,000 7 eee ) 0 0 1,800,000 1,800,000! 65,600 259,200 Oe ee 1,800,000 0 0 0 0 5,500 18,500 4 ae 1,800,000 500 0 3,600,000 0} 8,000 11,500 5 Cn 900,000 0 0 1,800,000 0} 3,500 9 ,000 DD oc hs 5,400,000 0 0 3,600,000 0} 18,500 - 14,500 ey a ee 1,800,000 0 0 0 0) 5,000 3,000 “ae ) 0 0 0 0 1,000 3,000 a 0 0 0} — 3,600,000 0! 3,000 3,000 oe ) 0 0} 0 0| 4,000 2,000 SeereDO) ek 0 0 0 0 0 500 0 0 0 0) 0 0 0 0 0 0 0 0 0 0 0 0 on 0 0 0 0 0 0 0 (0) 0 0 ) 0 Avérage...... ~ 199,038 75 640,384 7153 ,846 | 519,230 4,510 44,372 316 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 3 KS i) 2 23 = = S = = : = Be Eg s% ES S 25 me 38 $3 $3 $3 35 ss ahh 0 or ee + He o| OE nek ar vo li be Arye 0 0 0 0 14,400,000 0 See wD sectetct a 0) 0 0 0 6,000,000 0 SSP OD Bier amaiens 0 0 0 3,600,000 7,200,000 0 Hebi oincvrtee 0 0 0 0) 9,000 ,000 0 ee Sacer 0 0) 0 0 9 ,000 ,000 0 we WS eats 0 0 0 3,600,000 43,200,000 0 oi OL SURE 0 0 0 0) 0 0 Mar disse 0 0 0 0 0 0 = Seto ycasee 900,000 0 0 900,000 1,800,000 0 mac rel Ovesain ganna 5,400,000 0 0) 0) 17,100,000 0 faa, VA aioe 16,200,000 10) 10) 0 7,200,000 0 ead Ex2Osericene 0) O/| (0) 0) 2,700,000 0 AepEs nS asec ae 0 0 0 900,000 1,800,000 0 SR a ae 0 0 0 1,800,000 0) 0 Be gl OR ayanctcee 7,200,000 0 0 1,800,000 46,800,000 0 int RD Olaweiisl eek 0 0 900,000 13,500,000} 108,000,000 0 WER ZO Nis Rea ue 24,000,000} 1,800,000 0 23,400,000} 150,000,000 0 eae ORs her 7,200,000 0 1,800,000 70,200,000 50,400,000 0 Sty Mali diercrad vant 7,200,000 0 0) 34,200,000 21,600,000 0 ene 71 Ee ie 3,600,000 0) 0 5,400,000 3,600,000 0 tars): Wain ss 3,600,000 0 0) 3,600,000 14,400,000 (0) Jie. Yon baer 9 ,000 , 000 0 900,000 1,800,000 9 ,000 , 000 0 te wate ware 21,600,000 0 900,000 0) 21,600,000 0 cams Meese ts 10) 0) 10) 7,200,000 10,800,000 0 Migit2 Operiprac 1,800,000 0 (0) 10,800,000 10,800,000 0 Jarliyes s5 ects 1,800,000} 1,800,000 0) 1,800,000 3,600,000 0 Se ae re ea 1,800,000 900 ,000 0) 4,500,000 1,800,000 10) ip eee Say 75'600,000| 3;600,000} 10,800,000} 79,200,000} 25,200,000 0 SOR ete 5,400,000 0 1,800,000 900,000 1,800,000 0) LNG, Doncsioc 7,200,000 0 0) 9,000,000 12,600,000} 1,800,000 oy Ohmi Yichee 57,600,000 | 19,800,000 36,000,000 39 ,600 ,000 28,800,000} 1,800,000 So PL Orsne corse 7,300,000} 7,200,000 1,800,000 12,600,000 7,200,000 | 3,600,000 SEED Seed see 1,800,000 0 900,000 17,100,000 46,800,000 900 ,000 ie SO Rea 18,000,000| 3,600,000 2,700,000 54,000,000 46,800,000 | 7,200,000 Sept uOmmiaer 900 , 000 0) 8,100,000 12,600,000 50,400,000} 3,600,000 Cee Liat tele 0) 0 3,600,000 16,200,000 10,800,000} 1,800,000 piel 2 Osu tee 7,200,000 0 0 5,400,000 28 ,800 , 000 0 See MDH cher teas 10,800,000 0! 3,600,000 12 ,600,000 28,800,000 0 Oct (ZA acc aes 5,400,000 900,000 900,000 7,200,000 9,000,000} 1,800,000 Cina ilpeoes aise (0) 0) (0) 5,400,000 3,600,000 0 Pyne Si ensyaey 1,800,000 0 0 4,500,000 5,400,000 900,000 its CAS ata nee 0) 0 1,800,000 10,800,000 7,200,000 0 NON laches 0 0 0 1,800,000 10,800,000 0 $y Sie atte 0) 0) 0 1,800,000 0 0 cr Ges aKa 3,600,000 0 1,800,000 0| 21,600,000} 3,600,000 be EMO D at cea 3,600,000 0 0) 1,800,000 10,800,000 sage 7A nso, PS, 0) 0 0 0 7,200,000 DecisyGmenpise 0 0 0 0 12 ,600,000 lie eerie te 0 0 0 900,000 82,800,000 el loraa Stars 0 900,000 0 0 57,600,000 Gee haere 0 0 0 0 27,000,000 Average...... 61,230,769 778,846 1,505,769 9,276,923 21,450,000 519,235 TABLE ot/ I— continued. ORGANISMS PER CUBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on 1898 ee ee ee eee eee Bacillariacee Total 239,580 49,003,100 3,774,901 9,268,530 7,464,880 29 266,000 21,911,653 11,850,400 9,080,800 24/342 ,400 42/589, 120 18,693,300 8,760,120 36,990, 300 794,044'320 3,453,778,080 2,583 ,832,560 3,865 ,257,360 1,795,608 ,400 43,487,480 138,879,370 182,162,000 1,039 ,619 ,680 340,702,200 350,220,000 135,090,000 127,576,000 788,521,600 87,702,400 111,750,400 443,526,000 115,018,656 180,994,200 209,793,200 186,870,800 167,208,500 87,481,000 215,018,800 131,418,900 46,930,350 58,436,500 130,532,250 54,477,175 72'584'120 132/556 ,500 295'111,500 218/309; 400 308,149,750 864,280,915 332,305 ,000 239,550,800 396,192,727 filter-paper collections.) * 3 . o 3 8 = o ‘s 35 oS =: Re Re = 35 ee 58 55 SE ZS = Mw —=S = Ss S38 Ls Seq LB as a8 as SSS e§ fs = S g es i 146,280 0 0 0 10,000 1/200} 3,000,000| 12,000,000 0 0 10620 0| 0 0 29,025 | 5,500 0| 120,000 3,180 11,250 17,200 om 60,000 0 0 12'000| 7,200,000) 200/000 0 0 0 0| 14,400/000 0 78,975 0 0| 3,600,000 0 0 0 0 0 0 0 3,200; 8,100,000} 4,500,000 3,000 130,000 5,920 16,200,000 0 0 161,600 17'000| 10'800'000 0 0 72'500 42,320 900,000 60,000 0 15,600 170,500 22,500,000 | 0 19,920 40,000 | 24,059,000) 725,400,000 | 0 19,920 40,000 891,648,000 2,880,000,000} 1,800,000 374/080 200/000 197,683,200 891,000,000 | 18,000,000 924,800 390,000 27,175,680 2,668,000,000 | 10,800,000 14,469,120 255,960,000 19'699'200 1:260;,000;000 | 14; 4007000 388/800 4'110/400 15'080| ’ 18,000/000| 1,800'000 0 1'504'800 362'880| 88'200'000| 1'800/000 0 587.450 3,283,200| $5,800,000 0 0 434,000 336'194'880| 46/800/000 0 0 404000 | 100,320 0 0 0 199 ,800 34'560| 291,000,000} 1,800,000 0 220/000 3,840; 50,400,000! 1,800,000 | 0 50,000 0} _72/000/000| "900/000 0 120/000 0} 561,600'000| 3,600,000 0 0 0| 63/000/000 0 0 0 4,800} 54,000,000 0 0 0 1/200| 4017400/000| 3,600,000 0 0 0 97,200,000 0 0 0 0| 122'400'000 0 0 0 2,400, 93'600'000| 2,700,000 0 0 0} 115,200,000 0 0 0 (0) 66,400,000 10) 0 6,000 0 3,600,000 0} 0 0 0| 57/600;000 0 0 0 | 0| 37,800,000 0 0 0 0| 7'200'000 0 0 75,000 0 3,600,000 0 0 0 0| 25'200'000| 3,600,000 0 31,250 2,000! 14,400,000! 3,600,000 0 406,125 6000} 18'000/000| 7'200/000 0 609/000 0} 18'000'000| 5'400'000 0 1,866,500 0| 18'000000| 9'000'000 0 1711500 0; 151,200,000 0 0 2,254,000 6,000| 287,200,000 900,000 0 243,750 3/240) 811,000/000 0 0 75/625 10,500| 302'4001000! 900,000 0 105,000 800| 225;000/000 0) 0 20/000 28,860,160! 243,659,615, 2,471,923 311,593 5,234,484 318 TABUVE Il—continwed. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) * 2 3 gs ss S83 S84 23 e6 S&P > sé 8a eins ile Bas oe ) 0 ) ) Seedy Lae me ot 1,000 24,000,000 2,200 3,000,000 SOON i 9,090 0 49 ,536 0) Bebe rsiiac tien 2,204 10) 3,180 5,400,000 ¢ ese: 3,200 120,000 6,000 3,600,000 ce Dra meseee 2,800 14,400,000 48 ,000 0 Ca IAI) Ae ey (0) 0 120,042 0 Mar Le ates (0) 7,200,000 0 90,000 a f eraae es 0 3,600,000 0 1,800,000 pea SE A ee a 8,640 8,100,000 5,200 900,000 HS EDD ane 60,800 10,800,000 800 1,800,000 Se Oleh rae 30,240 2,700,000 1,000 900,000 Joye. eatin p 1,620 900,000 1,800 4,500,000 ee WALA acetate 3,960 1,620,000 0 4,500,000 STOO es Baas 2,800 7,200,000 3,600 3,600,000 By ed Oset erence 595,840 0 72,960 1,800,000 Many SipSictec es 230,400 9,000,000 552,960 6,000,000 etal! 0 peter ene 3,421,440 (0) 3,164,160 21,600,000 SOOT ites te 259,200 0 1,241,200] 64,800,000 Nae DAN ieee 109 ,040 10,800,000 , 126,720 9 ,000 , 000 ay NOME 293,360 1,008 , 000 101,760 5,400,000 Afb hsien oo 26,028,800) 103,320,000 998,400 1,800,000 Tet abe Iz: bests ae (0) 128,560,000 488 ,320 3,600,000 Se DIA a 32,114,880) 232,200,000 470,400 14,400,000 Seed Orhan eis 153,120 44,100,000 72,960 2,700,000 Jaa lyeer olsen 3,628,800) 70,200,000 34,560 7,200,000 Sh) als Dta ie, See 1,811,520 41,040,000 86,400 2,700,000 STO Vee 947,520] 115,200,000 5,600} 54,000,000 TD OM ines 133,920 20,200,000 1,000 3,600,000 Aig Dini. ieee 316,240 50,400,000 12,800 12,600,000 oe Oe Suede: 1,484,000 27,720,000 800 10,800,000 Cee LOMesr are 1,250,656 (0) 6,400 7,200,000 Feb Voie ene Sa 366,400 50,475,000 12,800 7,200,000 = ats Open nye 5,028,800} 104,490,000 (0) 3,600,000 Soi, Oocoaoses 1,122,000 56,250,000 0 5,400,000 ete LS Rosen or 1,200,000 64,800,000 7,000 16,200,000 SMSO (tena se 2,227,000] 33,480,000 30,000 1,800,000 CA RAT ees 5,499,840} 146,520,000 94,080 9,000 , 000 Octe) t4ise noe 805,800 40,500,000 18,900 9,900,000 Sy ig lg ete 840,000 37,800,000 55,350 0 CORT SH tai eat 436,650| 27,360,000 348,000] 12,600,000 eH pre ea uaTR a 736,000 56,700,000 214,500 5,400,000 INCA ts poses 83,200 3,600,000 70,550 12,600,000 Cnt) aa ty 98,700| 10,800,000 25,120] 19,800,000 diel Wale eee Bi 7,000 22,680,000 57,400 21,600,000 Se ee 60,000 194,400,000 0 23,400,000 DON RI 2,000 13,500,000 9,500 18,000,000 WECM ROM mee 0 5,400,000 (0) 6,300,000 Fase le hase seit 0 0) 0 6,300,000 Ker 8 OVh aia 0 4,500,000 0 4,500,000 Cee pacha ee 0 0) 0 2,700,000 Average...... 1,181,125| 34,762,365 148 ,626 8, 569 , 038 Surirella spiralis 2,016,000 9/043 ,200 3,801,600 86,400 14/400 28,800 57,600 127,200 20,800 3,200 3,600 1,600 400 4,000 800 800 2,400 6,400 800 1,500 5,000 17,600 2,000 3,500 8,000 2;000 12,500 19,000 6,000 4/000 3,500 1,500. 2/600 4/400 » 1/600 '308 ,330 TABLE 319 I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 1898 Average...... Synedra acus* 60,000 3,600/000 0 900,000 3,600 000 2}480/000 13,620/000 4/200/000 2,340,000 4/500/000 23,580,000 82,800,000 240,000,000 813,600,000 367,200,000 1,800,000 37,800 ;000 17,100,000 21,600;000 79' 200,000 5? 400/000 1,800,000 5' 400/000 39'600/000 900/000 0 0 5,400,000 0 6,300,000 3,600,000 7,200,000 16,200,000 1/800;000 42,300,000 1,800;000 13/500;000 27,000/000 5,400,000 16,200,000 37,800,000 23,400,000 30,600,000 8,100,000 27/000; 000 5,400; 000 10,800; 000 39,639,231 Conjugate Total 0 240,200 2,400 1,060 120/620 6,800 241,000 1,160 Closterium acerosum loot lelovoloy (ojfoys) rs oO Yolo) to of oo —~ S S = S) So S83 Se 8 xe = oS iS) gs aS = =38 Seu soy 2s se S S) A o 0) ) 0| 123,518,320 0 80 0 36,316,000 ) ) 0 43,464,482 0 100 0 21,691,300 ) 80 0 6,096,160 0 400 0 19,093,280 0 0 0 44,060,478 0 0 0 11,727,360 0 40 0 2,516,240 0 600! 200 22,368,600 0 400 0 29,817,200 400 600 ) 7,169,620 100 200 0 15,052,540 100 ) ) 29,011,320 800 400 ) 39,856,000 0| 3,200 0 94,337,920 0 0 0 | 1,081,381,200 ) 0 0| 222,233,400 1,600 800 0| 252,834,800 200! 6,000 Ole 421.475)-320 0 1,800 0 31,584,920 0 400 0 27,679,000 0] 1,800 0 49 614,800 G 300 0| 230,167,200 0 0 0! 191,626,440 0 ) 400 78,477,400 0 0 0 49 852,520 800 0 0} 295,478,560 0 0 0| 121,362,600 0 0 O| 112,224,400 0 0 0! 566,013,480 0 60 0| 166,746,460 0 0 O| 129,617,660 0 80 0 95,553,600 0 0 0| 137,009,680 500 60 0 50,995,120 2,500 120 0 65,106,000 6,400 200 0 46,830,100 1,000 500 500 49 825,580 1,000 80 0) 15,982,080 0 80 0 19,122,540 0 ) 0 6,776,060 500} 6,500 500 26,343,120 0} 1,000 0) 15,566,060 0} 1,000 ) 36,542,100 0| 2,000 0 24,435,040 0 20 0 74,444,400 0 0 ) 57,242,080 0 ) 0} 149,284,900 0) 0) 0| 116,833,160 ) 0 0) 68,456,620 305 556 31| 102,220,941 TABLE 320 I—continued. ORGANISMS PER CUBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 1898 een eee eee wee Mastigophora Total 122,484,100 36,086,000 43,208,127 20,321,700 5; 461,600 18/039/600 43/ 400,000 9,940,000 2,009 , 200 22,035,600 29,539,000 6,864,800 14,809,800 27,662,900 38,507,900 86,614,400 1,063 ,924,800 203,922,800 231,154,200 120,175,000 29,293,200 19,855,400 43,112,400 218,131,200 185,098,240 42,053,200 45,923,600 294,724,520 120,850,000 107,710,800 496,927,200 166,452,800 128,830,460 95,423,200 76,982,440 49/515 /000 63,144'000 45,854,000 48,193,000 15,129'540 17,367,000 5,416,500 25,325,500 14/564;000 36,011,000 23,494'000 73,719,000 56,400,500 148;740;000 116, 344/800 67,965,800 Bicoseca lacustris Se000 CO0OG0 C0000 CO0O0 ooo 460,800 3,801,600 432/000 86,400 72,000 14,400 ooooo oO ty) 7,500 0 218,400 251,000 486/000 25,000 13,500 2,000 0 oooo C00 95,852,602 112,896 Chilomonas paramecium oO C0000 COCO ooo 60,000 10,800,000 7,200,000 1,800,000 0 1,800,000 0 SOO09 CO000 C000 COCO 0 3,600,000 0 0 0 0 1,800,000 0 0 555,000 Dinobryon sertularia 8,000 1,806,400 2,764,800 16,153,600 43,200 3/600 247,200 69,600 407 ,602 Dinobryon sertularia var. angulatum oo -oooood. Coco sooo 35,040 598/400 0 4,432,000 0 0 0 14,400 0 12,000 172,800 Seceoo S0000 C2000 C000 COO0CO CooO 6 ,00' 101,358 Dinobryon sertularia divergens var. oOo 9SC0000 CO0O0 coco 8,000 1,555,200 2,104,100 39,648,000 1,584,000 18,000 56,000 16,000 0 47,040 866,083 = Pall TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. {An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) ES se § 1898 Ps AS Sige S353 Q ane 10. -:. : 0 =A GA eee eae 0 ee he eck 0 J eee 0 “a Sisk 0 “4 Sel Eee ee 0 See 0 eee eo cients 0 <2 Biever 0 oi In 0 wl eee 0 era Oe ste 0 SERENE viys Sa Us yo vi 0 et Pee eaae 10) “soak ee 9,960 7 icy Perea 1,830,400 WEE NE Ys Se 4,883,200 tO! os. 24,608,000 “1 ee 28,800 1 oe 0 oi SS ee 0 ENC! OTs... 5s: 0 So Se 0 SS mea: 0 2 ae 0 ETE EE Soe cis sc 0 oS ee ae 10) SC ae 0 aD Gis tare 0 PAGS MDS os Ss 0 iS Oe i.e 0 yf eee 10) ee Stee 10) S| Dee 0 Bevis O54). <2 0 et Sick, 0 per 2 Oe fs 42 0 RD Tine o's (0) Css ee 0 2 Cah ee 0 3 re 10) “Oi ae 0 (055 te Ieee 0 i pete res 0 73S een 0 ee 10) 1k eae 0 PRICE Osos ec 0 Se 0 ol an 22,000 Os ee 0 Average...... 603,911 Eudorina elegans oo o0o000 coo 240,000 240,000 48/800 32/800 1/000 400 9,600 60,000 30/400 4/000 400 800 7,600 4,000 8,000 400 800 3,200 2,400 40 500 2,000 1,600 on S loolelo Rol olololomg ol eolo) 14,362 acus Euglena m (=) eoooo o0o00oo CCOoO0oO COO co lo) ololo el olololo) > (>) o Euglena acus* 0 0 0 fy) 0 0 0 0 0 40,000 0 0 0 0 0 0 0 0 0 900,000 0 0 1,800,000 3,600,000 1,800,000 0 0 0 1,800,000 Euglena oxyuris _ io) oo _ (>) Oooo GoOCoceo Coo o Coco c! Goce Oo 3,20 eoooo C0C00oO 963 Euglena oxyuris* 40,00 180,00 ooo ocOoO0Cocoo ecC000 COCOCOCoO CcCcCcCoO COCO 1,800,000 0 0 3,600,000 3,600;000 1,800,000 3,600,000 3,600,000 120/000 4,500,000 5,400,000 3,600,000 1/800; 000 9,000; 000 2,700,000 1;800;000 900; 000 0 0 0 1,800,000 0 120,000 oooo 960,769 (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) ae TABLE I—continued. ORGANISMS PER CuBIc METER IN PLANKTON OF ILLINOIS RIVER IN 1898. Glenodinium cinctum Glenodinium cinctum* x 1898 8:8 8-8 Sy Sy. y Se) Venns) ils om cima 0 0) OS oilewsb arcane 0 0 Pee UD Deer nate 0 0) JN, aclsloc ae 0 0) it Bicae soe 0 0 tit Esha a ani (0) (0) SO RD ae arctan 0 0 Marie meer 0 0 os Seveersee (0) 0) St eben sree 200 0) Sth ge Dias Boye 400 0 Po tZOrrctensts 0) 0 prs eStore case 0 (0) Se DAs ceneleys 0 0 sp LORS mine 400 0 pa hyd Otsrocen nels 3,200 360,000 WER 9s aie grad 0 120,000 fe Alle ey perens 0) 120,000 Fe lies ch eat 0) 3,600,000 ene aD RN Set 0) 630,000 se ro eas eats (0) 60,000 \fena\er aiioroee acne 0 0 he MA ee eas 1,600 2,700,000 PAP SO HUES Bg 3,200 7,200,000 REPRE a 900,000 Jatly: 2 oieenoen 0 120,000 faa WADE eee ey vee 0 2,700,000 ae UO a 3 2,400 3,600,000 Bie A sons ef ee 3,200 14,400,000 PeNiblete, PAP cemious 1,600 7,200,000 oY io Sey eae 4,800 7,200,000 Sa eLlO teen oan 10) 5,400,000 eg ne Sia creparie 4,800 4,500,000 Sa ho Olen ieceiys 8,000 2,700,000 Sept elOe ac: 800 3,600,000 SOR LS rae 1,000 1,800,000 SEA De ee ee 3,000 0 aR heal 6,400 1,800,000 Oct wie at oe ) 6,300,000 im et a teeta 0) 120,000 agai alls} eet etree 0 0 fe) SD Ot Sears eae 0 0 INONjap oleae 0) 0) re Siensonetets 0 0 oh POs tee eee 0) 0 Driers 6) 0 PRD ON seer eante 0 0) Deck Owes. cae 0 0 Pi Sie seteneys 0 1,020,000 Sy SD Oe ees (0) 0 taal 1/ Doren erts 0 0 Average...... 8,653 Sil Ai (fey (Veveyey ~ iee)(=) on [o) oo oo0o0 CO00O0O Cc00o 452 oo (=) [o) [o) [o) ooo0o Ooo 0 200,000 240/000 4,260,000 240,000 240,000 120/000 240'000 0 0 0 90,000 ) 0 900,000 60,000 7,200,000 0 0 0 7,200,000 2'700;000 12,600,000 25,200,000 5,400,000 0) 900,000 900,000 0) 120,000 ) QOS, Oye) (o} 60,000 900,000 960,000 1,360,192 pectorale Gonium (eKfevevoey (=levokeKe) | (eveyiove) TeKeyio) to tO oN, ooo ooo 3,20 C000 CO00O C000 COCO CO0O00 COoO0ooOo CO00oO CoO 526 Lepocinclis ovum oo0c00o0o COCOOoo COO Conn ooo ooo oo0o0o0 o00o 3,719 Lepocinclis ovum* 0 0 0 0 0 0) 0 0 0 0 0 e 0 0 0 0 0 0 0 0 1,800, 00' 0 180,000 420,000 240,000 0 0 0 3,600,000 900;000 360,000 3,600,000 720/000 3,600,000 900/000 240,000 0 1,800,000 480,000 1,800,000 120,000 0 120,00 . 401,538 oooo o00°0°o S28 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) oooo0 o000oG C2300 o000 COOCOSoO ~” A) * S 8 8 = 3 8 zs 8 38 gs 3 =| =. | 28 1898 gS S§ =3 ‘S38 28 aes 33 NaS S83 ES 3 SS = & f= | 83 | 88 Ge SS 8 S83 S§ Se | 38 | 88 = © ny © a ee ee ea degre Waste ott FS... 0 0 400 (0) 0 0 0 (0) ae 0 0 100 0 100 0 0 0 ae 0 0 0 0 0 0 ) ae 0 0 0 0 0 0} 100 0 ) eae 0 0 400 0 0 0 0 0 eet sties. 0 0 0 0 0 0 0 0 Gy ae 0 0 0 0 0 0 0 0 3 0 0 400 0 0 0 0 ny) a 0 0 0 0 0 0 0 0 oi ae 0 0 600 0 0 0 0 0 Seige ts 0 0 0 0 0 0 0 0 ae +0 0 200 0 600 0 0 0 Me 5... | 0 0 200 0 0 0 0 0 i | 0 0 500 0 600 0 0 0 Sedu 2... ) 300 400 0 1,600 0 0 0 ee 0} 48,000 0 0 3/200 0 0 0 iy, 3.5: ...: 12,800] 48,400 0 0 3,200 0 0 0 = 0 0 0 0 0 0 0 0 ~ ee 0 s00 0 0 0 0 0 0 ey S 0 0 0 0 0 0) 0 0 ae 0 0 oO. 0 400 0 0 0 ee be) #835900 8,000 0) 120,000 200 0 0 0 a as 28;800| 60,000 om 900/000 8,800, 800 0 0 Reo). 28,800} 40,800 2,400 ~—1,200/000 8/800 | 0 0 0 aa 28/800 9600 8/800 792200000 4/800} 800 0 ny aaa 0 400 2,000, 5,400,000 4,800 0 0 0 a ae 0 800| 18,800! 10,800,000) 3,200) 400) 400 0 en 0 12,000) 491600} 86,400,000) 3,200! 400] 400 120 aan 0 63,200} 66,800} 15;300;000 6,800, 800 0 400 | | hi: ae 800 59,200} 12,000) 120,000} 11,200} 2,000 0 i ae | ny) 1,200 7,200 120/000 4°800 | 0 0 SS a | 0 0 3/200 0 8/000 | 0 0| ese 0) 2,400 6,400} 1,800,000} 4,800] 9800] 0 | 6 ets... 0 3/200 6,400 0 8/000 1,600 | 0 Sept. 6...... 0 2,400 0| 0| 12,800] 1,600 0 ei 3,000 0 0 0 3/000 1/000 0 i re 0 0) 1,500 0 7°000| ‘500 | 0 ae 1,600 100 4'800 0! 35,200] 4,800 | 0 | Rete, 42.0... 0 0) 0 0) 7,000 0 0 peatin.... 0 0) 0 0| 1/500 0 0 Bene. 2 ie. | 0 500 0 0 1/000. 0 0 See c 0 0 0 ny) 500 0 0 a 0 0 0) 0 500 0 0 a 0 0 0) 0| 1,000 | 0 0 | an | 0 0 om 0 1/000 0 0 ae 0 0 0) 0 | 0 0 0 ego, 0 0) 0 0} 0 | 0 0 DES tae 0 0 (6) 0 0 0 0 a 0 Oo 0 180,000 | 0 0 0 a 0 0 0) 0 0 0 0 7 0) ) 0) 0| ) 0 | } | | Average...... 17,520 | 6,957 3,711| 3,875,769 3,031] 298 17 11 | | | (22) 324 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) nm ] nm A) a = Sx 8 S Es ul) es 5 Sx = - ss = Ss SS 1898 Sx = o& =e ze 88 S38 $2 3 23 Ween aes oS oy 32 BS BS ee | Be. | 88 | Y Y Y } & ww w w fae 0 100 0 oO 0] 3,600 0 Dea | 0 5,600 0 0 0| 3/800 0 Bigeye | 0 7/740 0 0 ol tiger 0 een ee | 0 1,600 0 0 0| 4,600 480,000 ne | 0 800 0 0 0 800 60,000 (Sieece 0 10,800 0 0| 3,600,000| 28,800 0. Dok al 0 0 0 0 0 200,000 dee 800 | 8,800 0 0 0 800 900,000 Cait 400 8800 0 0 0 - 800 900/000 Peay 1,200 109/200 0 0 0 0 1,800/000 Bo Bae Se 0| 221/600 60,000 0 0 0} 10'800/000 AG es hs 0) 320/600 0 0 0 200 900,000 BL ae 0 166,600 ERO 200 0 0 1,800,000 Terres 100 17/300 0 0 0 0 0 HGiiw eae) 0 126/000 60,000 0 0 0 9,000,000 Dike age | 0 121/600 120/000 0 0 0 4'500;000 | sie aay 0 102,400 0 0 0| 3,200 3,600,000 Orie sce, | 0| 38/400 0 0 0 0 9000/000 (ere | 0 21600 0 0|% 3,600,000 0| 14'4007000 Se eetlies | 0 1/400 0 0 0 200 360,000 ieee 0 200 0 0 60,000 0 180/000 Teather 0 0 0 0 0 0 4,500,000 (ee 0 0 0 0 120,000 0 7’200'000 ite 0 1,600 0 800| 7,200;000 0| 1471600/000 Dome 0 800 0 0} 67300;000 0| 38,700,000 Sein 0 0 0 400, 1,800,000 0 1,800,000 Deeeea 0 1,200 0 800} "900,000 | 0} 10/800/000 LOR 0 0 0 800 3,600,000 0) 86/400/000 Doce 0 0 0| 2,000} 3,600,000} 9,200} 42/300;000 De ca 0. 0 0| 12,800 600,000 800} 18,000,000 Sree 0) 0 0 800 3,600,000 0| 252'000/000 one 0 0 0} 4,000} 37600000} 1,600} 93/600/000 ene ees 0 0 0| 3/200) 1'800'000 800} 65,700,000 BOs aca 0 0 0} 87300! 17800/000| 1,600} 18;000/000 | | Gate 0 0 0| 4,000) 5,400,000 800| 16,200,000 iio 0 0 0 0 0| 1,000 6,300,000 Zam ae! 0 4,000 o| 1,500 0. 0 1/800/000 a7 ran 0 17600 0} 4'800| 3,600,000} 1,600 9'000/000 ere oy 0 0 500! 1,800,000 0) 11,700,000 Tig ee 0 0 0 0 120/000 0 18001000 Spero | 0 0 0 0 900/000 0| 277007000 Diente | 0 500 0 0 0 0 5'400/000 ARONA | 0 2,000 0 0 120,000 | 0 1,800,000 sie |< 1,000 | 16/000 0 0| 0 0 1'800/000 Aor k rs 0. 9/000 | 0 0. 0 0 0 Dh aes Gs 0| 947000 | 0 0 1,800,000 0 5,400,000 Nek 4,500} 1,999,500 1,320,000 0 0) 0 3,600,000 GER, 13,500] 1,693,500} 2,280,000 0) 0 | 0 900,000 13 | 2/000 781000 |. 2'760/000 | 0 0 500 2, 400/000 20e2 ie 6'200| 2,764'800 900/000 | 0 0 0 0 Diente 800| °395'200| 300,000 | 0 0 0 2,700,000 » | | Average...... | 625 179,138 | 150,000! 873| 1,094,615/ 1,251| 17,672,692 | | ——— a sz \ 325 ] ' ‘ ? TABLE I—continued. ' ORGANISMS PER CuBic METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on ; filter-paper collections.) ; ] ; = = q 8 a | ~ 8 = S 8 S 3 x = Werke eS 3s 3 S$ S a) S83 Sa 8% = 8 1898 © ss as QS R32 S38 ss | 3s =5 =8 = % gS ese SS ey S $s 8-8 $3 Es zés oS ey | ESS Be oie = 2 G 8 3 isa) cs Se a 8 Tan. 11...... 440,500 100 0 ) 0 0 ) 0 > 32,800 100 200 0 0 100 0 0 ae wa 66,338 387 387 387 1,161 20,898 774] 1,935 Toy eeneee 122,900 ) 0 0 0 1,300 0}. 0 oS 4,880 0 0 0 0 ” 3,200 0) 0 eA. St 52 34,880 800 0) 800 300 ) 80 on 141,524 632 25.272 12,636 9,477 3,159 0 0 Li ee 11,200 400 0 400 400 400 0) 0 a 11,720 400 0 400 1,200 0 400 40 ie 7,600 600 0) ) 400 0 0 0 26 ee 4,800 400 ) 0 ) 0 0) 0 DTS coy: 61,400 400 (0) 200 ) 0) 0) 0 Deter 700 100 100 100 0 0 ) 0 AP 3,520 300 200 (0) 20 100 0 0 i ee 7,300 400 0 0) 0 400 400 | 0 Bora... 6,720 0 (0) 0 ) 0 0) 0 So eee 26,000 (0) 0 (0) 400 0 0| 0 i. ae 49 ,800 ) 0 0 1,600 0) 0 0 Wien 23,800 2,400 0 0 300 0) 0 0 Dies eee 9,320 600 ) 0 200 0 400 80 Bites. aS. 8,920 400 ) 200 ) 0 400} 200 7 cee 23,600 800 200 0 ) ) 0} 3,200 Fees, 2 21,600 1,600 800 ) ) 0 0 ) 2 ee 21,600 1,600 800 ) 0) 0) 800 0 2S aes 37,000 800 ) 0) 0 0) 800 100 eee 3 19,360 0 0) 1,200 400 0 400 400 HOS : 26,000 800 0 800 200 0| 1,600} 1,200 ROM 28,800 0 800 400 400 0 400 | 0 2X5 pe 4,800 400 400 0 0 0) 400 0 ae 16,800 800 4,800 0 ) 1,600 0 ) To ieee 7,280 ) 1,600 0 400 1,600 40 40 HOP es 24,060 0 2,400 800 0 800 0} 800 Daa 36,800 800 5,600 ) 0) 800 0) 0 OSes: < 23,200 800 5,600 0) 0 1,600 0 ) (oye aae 20,800 800 300 800 0 3,200 0} 1,600 Rom 3. 28,000 500 500 ) ) 6,000 0| 1,000 20) ee 19,000 500 500 500 500 1,000) 1,500 500 Dip arc. 4.: 59,200 1,600 1,600 0) 0 | 8,000 0} 3,200 ee ae 912,580 0 40 | 0 40 500 500 0 i an 9 ,000 0 1,000. 0 | 0 | 0 0) ) ihe oe 10,000 0 ) 0| 500 | 2,000 | 1,000 0) Die eae 25,060 1,000 1,500 | 1,000 1,000 | 500 500 500 | Tt eames 32,060 500 1,000 1,000 2,000 500 0 500 SB 37,060 1,000 1,000 1,000 1,000 0) 0} 1,000 it ee 42,000 1,000 0 5,000 | 4,000 0 0| 0 Gee 190,400 | om 0 | 2,000 4,000 | 6,000 0) ) BO « 3,400 0 0} 0| 500 | 500 0) 0 Bek, ot). 121,000 0 0) 0 0| 1,000 0 ) 2g ee 600 0 0) 0) 0 | 600 0| ) Done; 1,040 40 | 0. 0) 0) 1,000) 0) 0 2 ae 220 0 0| 0 0| ) 0 0 Average...... 55,364 465| 1,098 | 570 604) 1,284) 198] 315 326 TABLE I—continued. ORGANISMS PER CuBic METER IN PLANKTON OF ILLINOIS RIVER IN 1898. F (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 2 8 ER 3 Ss = 3 3 = $s i) . 1898 3.9 -S 5 US 8 es 8 ~S = 5 LS LB Soe 3 38 3 a aS S5 SS ss 3S 8 as aa | Ss rs Bs Sa ee S38 BS eo) 8s Q Q Q a z a x 16) Jane Ath ee, 100 100 0) 0 ) 593,420 0} 26,500 CNN et a ee 400 200 0) 0 0 197,100 0| 37,000 SOG ear an OMG EGOS 0) 0 0 190,017 |13,545| 45,666 Beha aie 500 100 0 0) 0 1,246,300] 1,600] 54,700 AGNES pee ee 800 80 0 0) 0 629,680| 800] 197,600 en HIS ON ie 9,200| 2,000 0) 0 ) 1,016,000] 4,400] 164,800 Lie Bite 6,318 632 0 0 518,954 0| 50,544 Mar, sie teyou 4,000 800 400 0 0 1,773,360| 400] 46,400 Uy Gen eau 2,800 800 40 0) ) 492,920} 800] 54,800 ce a isneaee i 2,600} 1,400 ty) 200 0 324,200} 200] 89,600 SA YS te 1,600 300 0} 2,000 0) 267,800} 400| 22,000 DO ue he 200 0) 0 400 0) 241,420] 400] 10,200 Apres Sect e 100 0) 0 500 0 241,440 0 3,100 SD eae 1,000 800 0) 100 0 1,342,500] 300 2,400 STEKO dae 1,600] 1,200 100 0 ) 1,340,800 0| 13,200 OS DR. os 5 3,200 @| &,2C0) ty) 7,710,400 0} 99,200 Mayor Sera 22,400} 3,200 ) 0 0| 17,404,800 0} 83,200 Fie al oes 30,400 3,200 0 0| 18,260,800 0 6,400 a Gp ee ae 800 800 0) 0 0} 21,654,400) 1,600 0 CO DA ek Rta 3,640 200 200 ) 0 990,800 ) 200 ci Sf ame oh 3,840 400 ty) 0 ty) 2,282,400 0) 600 June “Jae 9,600} 8,000 200 0 ) 7,800,000 0) ) CE Nall Su 5/600] 1,600 800 0 0 6,480,000 0 0 SVD pee ieee 5,600 800 0| 3,200! 3,200| 12,010,400 0) 0 Eton 9 Ger Miter | 14/400} 2,400 100 0 0 6,491,200 0) 9,600 July. Ss. 4le. 8,800} 2,000 160 0 0 495,640 0) ) TOA pee 10,000} 2,400 300 400 400 3,900,920 0 400 LONGO eee: 12/300] 2,000 0| 2,000 2,000 721,640 0) 400 CRD Grea 2,400 400 0| 14,400 14/400 487,000 0 ) IG Deg 3 i 5,600 800 0| 17,600 17,600 4,474,400 0 0 CeO Oona | 2'3800 400 0| 78,400 78,400| 69,000,200 0) 0) UD oes tian | 8/000 g00| 3,200] 13,600 13,600 253,600 0 ) OS ERs Ae 12,800 0| 2,400] 20,800 20,800 728,000 0 1,600 CONT SO) cos ale 6,400 800 800} 7,200 7,200 122,400 0 0 Sept, 6.080... 5,600 0 g00| 4,800 4,800| 120,001,640 0) 800 SE AIS tr es 11,500 0 500 500 500 1,451,120 0 9,000 SD Oana 8,500 | 500 0} 18,000 18,000) 1,923,500 0 2,500 CGD aban ee 25,600} 1,600) 1,600] 65,000 65,600 851,400 0 0 Oct teen 8 ,000 500 500 0) 0) 720,000 0) 0 Si Tileiee gotee 2,500| 1,000 0) 0 0 843,540 0 3,500 EOmn ig Cegtea 2,000| 1,000 0) 500 500 1,744,000 500 5,000 DIG a 15,000 0 60 500 500 1,334,000 500| 35,000 Now aisle oe 15,000|} 1,000 60 0) Q 985,560| 2,000} 31,000 ol Reinet 5,000} 2,000} 2,000 0 0 965,000 0] 22,000 ~ SS tar eat 17,000} 2,000 0) 0 488,100] 1,000} 28,000 A Ris Pato 48,000 | 8,000 400 ty) 0) 750,640} 4,000| 108,000 oa Bch ae Ob 200 0 200 0) 0) 721,500 0| 47,500 ESS Gesasse 0) 0 0 0 0) 720,580| ~- 40 7,000 Leh amen 0 0 0 0) 0] + 1,573,800 100| 16,400 CIES () Bete ag 0) 0 ) 0) 0) 487.120 0} 16,600 Heo} pears | 200 0 0 ) 0 490,600} 200) 28,000 | Average...... a Mev || = silks 368| 4,871 4,760| 15,812,346| 630| 26,546 a2) TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) * x = = 3 3 3 2 SS 2 | 38 e : 1898 See ee: | Ok | ae |) ok : 8s Ss =5 = e2 | ge chs as 8 8 SS oy | SS eis She & S = i) & S RS 2 S teh oS Vega eee 300 80,000 300 6) ‘0 0 6,580 0 ERA ieee sacs 300 40,000} 28,800 0 100 0 49 ,240 0 ee ee ae 58,437 O} 11,997 0 0 0 126,603 0 Feb e Sis a. as 5,900 0 1,000 0 0 0 11,496 0 rs Serrenctcis 8,000 10) 800 10) 0) 0 14,160 0 Sy ge a ae 5,200 0) 800 0) 0 10) 31,040 0 Se 15,795 720,000 0 0) 0 0 48 ,649 0 le ills cee 10,000 0 0 0} 1,600} 1,600 20,400 400 Se Browete ts 8,400 10) 520 0| 1,600} 1,600 29,200 800 See | 33,200 0 1,000 (0) 400 400 103 ,940 400 OD animate 41,600 60,000 80 0} 1,200} 1,200 185 ,520 400 ae 29a 30,400 0 0 200 200 115,880 5,020 i eee 20,500 0 20 300}. 100 0 84,820 1,800 0 eae 20,100 900,000 0 200 100 0 54,540 0 BeOS ris ane 453,600 0 0 400 0 0 749 ,000 0 PI EAO tcc. aos 614,400 0 0 12,800 0 0} 2,892,360 4,800 Ma ee 736,000 0 0| 720,000 0 0} 5,247,800 0 Os oes 78,400 0 0 24,000 0 0} 2,663,400 200 2 a eee 72,000 0 0 10,400 800 800 1,465,500 800 OT ee 74,200 0 0 400 0 0 196 ,020 3,200 Rem RSL 3) 5 G% 61,200 0 0 400 200 200 180,760 18,800 | ea ee 1,499,200 60,000 0 14,400 0 10) 903 ,000 392 ,000 2 by 532,800 | 10) 10) 104,000 0 0 639,600 1,600 oS Gh alae 195,200 | 0 0 74,400} 800 0| 2,601,200 3,200 eM Sars, se 45,600 | 3,600,000 0 33,600 0 O} 1,118,400 ji See 13,600 0) 0 4,800| 7,200! 7,200 153,000 800 i 317 eee 35,600 | 2,700,000 0 5 ,600 400 400 184,500 0 OR 24,000 0 0) 2,800 400 400 946 ,080 0 BeO:! St. A. 2,000 120,000 0 3,600 (0) 10} 370,200 0 ce ay ee 23,200 1,800,000 0 95,200 0 0 1,294,240 0 as OP euetes + 8,400 10) 0 4,800 (0) 0 782,720 0 Be LOnss 20,000 0) 0 8,800 0) 0 935,380 0 Bee Siete 26,400 | (0) 0 5,600} 1,600) 1,600 696,180 1,600 E10) 3 51,200 0) 0 800 0 0 435,080 1,600 DEMO. a. ea 13,600 0 40 0 (0) (0) 422,840 0) aloes ae 49 ,000 0 120 2,000 0 0 197 ,960 0 “10 eee 34,500 0 0 20,000 | 500 0 475,860 1,000 OH See 92,800 0 200 22,400 0 0 1,792,700 14,400 Oct ene ere 23,000 0 10) 1,500 0 | 0 105,020 2,580 pellet. 23,000 0 40 500 0 0 122 ,000 2,000 ee USiere nk.» 47 ,000 900,000 | 0 1,000 40 40 159,200 0 oP 7 a 23,000 0 0 0 0 0 1,048 ,620 0 ronnie Le cic 12,500 10) 60 0 0 0 156,300 0 ee che Steps 70,000 0 0) 0 0 0 147,780 0 bee 5s. 35,000 0 100 0 0 0 180,600 0 “Dee 2,000 10) 0 0 0 0 128,400 0 DOO So c-< 2,000 0 0) 0 0 0 66,000 | 0 Cs Os ose 2 40 0 0 0 0 0 64,280 0 NES pee 300 1,080,000 0 0 0 0 159,740 | 0 pee O aris. 200 120,000 0 0 0 0 191,320 | 0 SMM Tye a iS) 3 200 120,000 0 0 0 0 50,540 200 | | | Average...... 101,024} 255,769, 882 | 332 301 | 592,416 | LAB EE 328 I—continued. ORGANISMS PER CUBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) is} 2 ~” 8 2 xs aR 3 sf S & 3 1898 8 aS & Sauer ~ s ss S & S.R = Se os Ss a's Ss 28 28 ae me | Bo SS gs s8 3 ss ES IS SES) S Soy nals é a* | 8s 2 é = hamelile sees 0) 0 400 0) 0 400 6,180 0. ie hla ae 0) 0) 45,100 0 0) 44,500 4,040 0 ES RDIS CaS | 0 0) 90,171 0 0) 89,379 352m 0 et en Wisi aaah 0) 0) 3,800 0 | 0) 3,800 7,696 0 SOEs Suite 0) 0) 6,800 0) 0 6,800 7,360 0 eNO Bea 0 0) 18 , 000 0) 0 27,000 12,240 0 Coe Daa Aa 0 0) D5 YD 0) 0) 25,272 Ne Oi 0) Mart ae 0) 0) 1,600 0} 400 800 18,320 0 Go Weigh La 400 0) 4,040 ) 40 4,000 23,960 400 CLP bis RO 0) 400 22,160 30| 400 19,200 80,980 40 COED) a. 0 400 10,440 0) 40 10,400 174,680 400 Sie Ole a Wag 0) 20 1,620 0 20 1,600 109,240 200 More, © Sats wane 0) 0 1,100 0) 0 1,100 81,920 600 CTO pA eas 0) 0) 960 0) 60 800 53,480 600 ESSA i aah 0 400 3,300 400 100 16,000 745,300 2,000 ERG! Anat 0 3,200 4,640 0} 640 3,200| 2,889,720 3,200 Wine “Bes aos ) 0) 16,000 0) 0) 12,800) 5,231,800 22,400 Se Oe Mie tee, 0) 200 14,400 0} 1,600 11,200] 2,647,200 35,600 peel in ea tae 0) 800 20,800 0| 6,400 10,400] 1,438,300 22,400 SO a oe 0) 3,200 1,040 0) ||, S20 400 191,780 4,000 os SO eegr al 0) 18,600 880 80] 200 600 161,080 1,400 jane 0) 392,000 800 0} 800 0 507,000 1,600 Spelat At coats tai 0 1,600 600 0} 400 200 637,400 800 Sei raw 3,200 0) 1,100 0} 300 800} 2,593,600 0 NS IW aes ise 0) ) 1,900 0}; 800 300} 1,112,500 0 icilyaaeo eee 0) 800 2,480 80| 1,600 800 146,920 ) Crip iee ta 0) ) 4,800 400 | 2,000 2,400 178,100 0 OS [0 comabaate 0 0) 2,760| 1,600| 360 800 933,320 0 toma 0) 0 120 0 ) 60 268,480 1) ING, Diego oat 0) 0 1,400 0 560 40| 1,260,840 0 eNO 0 0) 1.200 0) 0) 12,000 775,920 0 Sooke a ame 0) 0) 4,120 0) 120 4,000 907,260 0 Mh pac tiatte Mle NG 1,600 0 5,720 0) 60 5,600 671,260 0 OP (Oe ee 1,600 0) 4,080 0) 80 2,400 415,000 ) Sete Goaacoe 0) 0) 9,640 | 2,400 40 4,800 413,200 ) LOM Siete ei 0 0) 21,000 500 | 1,500 17,500 171,960 0 SEE DOV ac wioes / 1,000 |- 0) 6,000| 1,500] 500 3,000 460,360 0 NC ACI aaa bs 14; 400 0) 13,300} 8,000] 300 4,800| 1,744,200 0) Oe Boos 2,500 0) 2,280 | 2,000 120 160 97,160 0) inte payee 2,000 ) 2,000 | 1,000 500 500 115,500 0 ComatiGete uae 0) ) 540 ) 40 0) 188,160 0) enol Se Wlaah 0) 0) 3,500 0| 1,000 2,500) 1,045,120 0) Noi de dcaane 0 0) 3,060 0) 60 3,000 152,680 ) Ee ROT PAS, 0) ) 1,180 120 60 1,000 146,600 ) He vitigp ure anal 0 0 100 0 100 0 180,500 0 ae he 0 0) 400 0] 400 0 126,000 ) fh 3. Oe wie 0) 0) 0) 0) 0) 0) 66,000 0 TOs Gopanck 0 0 20 0) 0) 20 64,260 0. TAR eU ate 0) 0) 600 0) 0) 600} 159,140 0 Lu ONaea ee 0) 0 0) 0) 0) 0) 191,320 Q Dane sash 200 0) 20 0) 20 0) 50,120 20 Average...... 517 8,108 405,983 351 425 571,611 1,839 — a29 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON oF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 1} u 38 3.8 3 ; s 3 2 8 AS S58 Ray ‘<8 ws as ® ha 5 1898 Beas 382 sss 28 INES es oS en: Bao rhe eS see 8 anes Sees | Ss See ips keen SS, less oe) Sop = oP 5% Ses TS = ey leurs x a ee < G Hans silty 5.4 0 0 | 0 10) 0) 100 | 100 VS as Grea 300 10) 0) 300 100 0 0 1s NR Se 387 0 1,661 2,048 0) 10) 10) BGI eae) oe, --s 500 10) 100 600 300 10) 0 pen... 0 0 80 80 0 0 0 peeeies 80 0 0 80 0 0 0 peas. 0 0 0 0 0 0 0 Max, 1...... 400 0 80 480 0 0 0 Sesh... goo 0) 1,200 2,000 1,600 0 0 BeOS ie ke. 2,200 0 600 2,800 1,400 0 0 "PS ee 3,200 10) 800 4,000 2,800 0) 10) Se 2,600 0 600 3,200 200 10) 0 A= ane 0 1,700 400 2,100 600 10) 0 7S alee 1,800 0 400 2,200 800 0 0) RMR :.) so 12 ,400 (0) 2,800 15,200 8,800 0 10) O° ae 12,800 121,000 4,000 137,800 57,800 0) 10) a Se 222,400 745,600 54,400| 1,022,400]! 552,200 1) ) 2 0 eee 134,400 790,400 220,800} 1,145,600 643,200 0) 0 EN 8 ahs 91,200 295 ,600 48 ,000 434,800 160,000 0 0 > 2 ie 1,000 18 , 400 1,800 21,200 7,200 (0) 10) eos mo. 1,400 9,200 600 11,200 3,400 10) 0 Mane 7.2... 0 32,000 0 32,000 3,200 0 0 “See 0) 28,000 1,600 29,600 7,800 10) 2,400 +. aa ee 10) 150,400 222,400 372,800 148 , 800 9,600 8,800 BeMLIG ecys- sc. < 0 48 ,800 117,600 166,400 20,800 7,200 MBetlyon Sis oa. 0) 2,800 7,200 10,000 1,600 800 2" a Sierra (0) 2,000 8,000 10,000 4,000 1,200 2 ae 0 2,000 15,200 17,200 5,600 4,000 Bee DOi Ne afc: 0) 0 1,200 1,200 0 0) Bite 2222... 0 0 0 0 0 4,800 = 2S ace (0) (0) (0) 0) 0 2,000 Stree. 2 0 0) 0) 0) 10) 16,000 2 Ee 0) 10) 10) 0 0 9,600 * QUE eee 0 0) 0) (0) 0) 800 ‘S312 Cees 0 19) 0) 0 0 (0) *: alee (0) 500 0) 500 0, 1,000 weer ORs.) 0 3,500 8,500 12,000 6,000 4,000 / 0 19} 200 35,200 54,400| 16,000} 43,200| 54,400 Ole, eee 0) 4,000 2,000 4,000 500 2,000 (Sint Peete 0 7,000 2000 9/000 4,500 500 nl ee 10) 17,500 7,000 24,500 10,500 3,500 * laa 500 9,000 19,000 28,500 7,000} 13,500 Bows foc... 500 0 1,000 1,500 0 500 WOES isco: «.: 0 0 0) 10) 0) (0) > Ae eee 0) 0) 0 0 0 10) “2 ean aee 0] 10) 0 0) co 0 ie 500 1,000 8,500 10,000 500 0 Mee 6... ... 0) 1,000 1,020 2,200 Os) 0) PES ey cs. 5 500 1,700 5,100 7,300 1,800 0 2 20a 0) 3,600 1,600 5,200 2,600 0 eee 0 200 0 200 10) 0 | | Average...... 9,421 44,540 | 15,432 69,165 32),.398 2,390 } | ! ft 2B yEse 330 IlI— continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) ° 1898 Asplanchna brightwellii a (=) oo (SSKSVoy (eveyolore) = (a(Soey (Soyo) fon) oo oCo0o0 C0000 2,079 a 2 Say 2 op 2. § 3.2 ESBS | Ss Sis 3k 2.8 Qs ASSES ss Sas SS SS os 8.8 S& S OH a8h 2k | 8s Fs SS Se | % —Q [SI 0 (0) 0 (0) 0) (0) 0 0) 0) 387 0 387 (0) 0 0 0 0) 0) 0 (0) 0 0) (0) 0 0 (0) 10) (0) 0 (0) 10) 0 0 0 0 0) 0 0) 0 (0) 0 0 0 0 10) (0) 0) 0 0 100 (0) 100 0 0 0 0) (0) 10) 0 0 10} 0 0 0) 10) 0 10} 0) 3,200 1,600 0 1,600 14,400 (0) 800 800 PR AVA) 0 200 200 2,000 | 1,400 0) 1,400 0 4,800 0) 4,800 0 4,000 0 4,000 1,100 70,400 0 70,400 10) 544,000 10) 544,000 | 0) 29,200 400 29,600 0) 51/200 0 51,200 (0) 300,800 34,800 335,600 0 6,400 10,400 16,800 0) 10,400 93,600 103 ,200 0 229 ,200 64,800 292,600 0 272,800 80,800 353,600 0) 77,600 138,400 216,000 0 28,800 86,400 115,200 0 80,000 83,200 163,200 60 27/000 10,000 36,500 60 87,500 27,500 115,000 0 409 ,600 84,800 494,400 0 | 19,000 9,000 28,000 0 8/000 1,000 9/000 0} 8,000 500 8,500 0 11,500 10) 11,500 0 1,000 0 1,000 0 0 (0) 0) 0 100 0 100 0) 0) 0 (0) 0 0) 0 0 0 20 0 20 0) 0 0 0 0 400 0 400 0 0 0 0 441 43,946 13,973 57,919 Total eggs Brachtonus angularis leovelove) TeleVoleo Welelololey (ere\iovey (=(oNe} 1,600 13,200 72,800 1,200 | 12,000 105/600 | 116,000 42400 | 28,000 35,200 18,000 43,000 41,600 2,000 2/000 2/500 5/500 oeo0o0o0 C0000 13,242 Brachionus | bakeri var. brevispinus SSO s See. (cic i rs So Ooo SOO clo. COC So Ccoco ooqoo /’S S000 C0000 coco 139 1898 Average...... .| 331 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) Brachionus bakeri var. clunior- bicularis r= ~ lo) oo0o00 CO0000 c0CCo ve) oO oooo o0o000co coco o000o C0oco Coco Brachionus bakeri , var. melhem1 oooo oo0oc0oo oc000 C000.) |6cCOCmCOCUmUOKUUMOmUDUCUCOOCOCOOOUUCUCCOCOOUUMUmWUDCUCOCOOUCUOUUDDUCOCOOCOCOUDUCM OOD CU OOOOm CUOO OF rs vo} z g : Pes 2 g 2 8 % Soe S as = 8 =oos = 3 8 eas Sy: > = “3 ad toe — o S's 8 Sse | S882 | $85 | $85 69 69 | oo a 0) 0) 0) 0 | 0 0 0) 0 0 0 0 0 0| 0} 0 ) 0 ) 0 | 0 ) 0 ) 07 0 ) 0 0) 0 0 0 0) 0) 0. 0 0 0 0) ) 0 0 0 0 0 0 0 ) 0 0 0 0 0 0 40 0 0 0 0 0 0 0. 0 ) 0 fy) 0 0 fy) 0 a) 0 0 0 0) 0 0 0 0 0 0 0 0 0) 0 0 0 fy) 0 0 0 0 fy) 0) 0 0 0 0) 0 ny) 0 0 0 0O. 40 0 0 fy) 0) 0 0 0 0 0! 0 0 0 0 0| 0 0 0 0 100 | 900 0 0 0 400 | 800 400 0 0 1,200 1,660 60 40 0 ) 2,160 2,520 ) 0 0 0 0 ) 0 0 0 0 40 0 840 800 0 1,600 0 2,400 5,600 ) 0 0 0 0 800 800 800 5,600 2,400 800 1,600 4,000 7,600 5,600 0 2,000 0 4,500 4,000 0 0) 0) 500 500 ) ) 1,600 3,200 0 0 0 0 ilies 0 ) 0) ) 0 0 0 40 | 0| 40 0 500 0| ) 500 | 0) 0 60 0 60 0 0 0 0 0 0 0 0 0 0 0 0 ) 0 0 0 fy) 0 0 0 | 0 0) ) 0 | 0 0 0 0 0 0 0 0 0 0) 0 0 0) 0 0) 0 0 41 118 155) 592 420 ao2 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 1898 Brachionus buda pestt- nens1s eee), Hever) SlSKtoyey Te(SVKenevS) Gh ala MSS) GOI ees Cure) | Se desl s2 | = gree as 88 | Se BS io) eicowed eo | 32 | fa | Sgat (SS! as a* aS gers hee 0) 0) 20 20 20 0) ) 100 | 0) 0 0) 0 ) 0 387 ) ) 0) 0} 200 0) ) 0 0 0) 0 ) 0 ) 0 ) ) ) 0 0) 0 ) 80 0 ) 0 0) ) 0 80 0) ) 160 0 360 0) 0) ) 0| 1,720 0) 0 200 0 140 0 0 0 20 100 ) 0) 200 120 160 0 0) 2,800 1,200 800 ) 0 57,920 97,600| 4,000 0 () 32,000} 419,200 0 ) ) 19,200 57,600 0) ) 0 5,600 69,600 300 200 0 30 200 0 0) 0) 0 0 ) ) 0 200 0 () 0 0 0 0 0 0 ) 300 200 0 0) 0 ) 0) 0) 40 0 40 0 0 120 0 0 0 ) 80 0) 800 5,600 0 0 0 0 120 0 0 40 0 6,400 0 0) 200 1,200 2,000 0 ) 300 300 37,600 0 300 0 0 35,200 0 3,200 300 800 32,000 0 1,600 0 0 19,200 ) 0) 70 500 4,000 ) 500 500 9,000 0) 1,600| 4,800 4,800 78,400 ) 0 0 40 1,000 0 0) ) 500 0) ) 0 0) 500 30 0 0 0 3,500 5,000 0 ) 0 () 0) 0 0 0 ) 180 | 0 0 0 1,000 100) 0 ) 0) 400 400 0 0) ) 1,000 500 0 0 0 320 1,160 20 ) 0 2,400 3,200 0 0 0 1,200 606 | 0 0) 0 400 200 40 147 137 2,693 17,071 170 Brachionus pala var. forma dorcas spinosus o o000 9000 1,70 CGooo eoooeo coooeo cooo coooo ocoooo coco coCceoo ocoooe coo][e w w Brachionus Total pala 451,200 76,800 77,700 280 0 200 1,000 303 TABLE I—continued. ORGANISMS PER Cusic METER IN PLANKTON oF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 2 » * n te = = = = On 1898 os 8S }88 §|] sss 38 oss 28 SE as =S | 28,2 Ss. =iS5 Ss 8.8 Sn aS Ss SORES Sok eSs eSs ot So 8 mo See Sees oeee | Sees (sae | SS [See = 9 Say Q a a Sa ca PORT 2: 100 0 ) 0 0 0) ) 100 BID. .,* 100 0 ) 40 40 0 0| 0 oh eee 1,161 0 0 0 0 0) Oo. 1,548 Bian: ) 0 0 0) 0 0 0) 100 BEGoes: 0 0 0 0 fy) 0 Oo 0 ig pao 800 0 0 0 0 0 0 2,400 Te a 632 0 0 0 ) 0 0 3,791 480 0) 0 80 80 0) 0) 480 160 0 0 0 0) ) ) 840 1,000 0| 0 160 160 , .& 0 400 2,920 0. 0) 2,000 2,000 400 0 440 420 0 0 1,800 1,800) 1,200 | 0 20 , 20 0 0 700 700 | 400 | 0 120 i oe 240 0 0 140 140 60 0 200 Cae 5,200 0 0) 400 400 0) 0 0) Bane ves 324,280 oO 0) 6,400 6,400 ) 0| 0) ait oes 661,200 Oo 0 om 0 ) ) 41,600 HORS. 118,400 0) 0) 0| 0 ) 0) 9,600 ei 101,700 0 0) 0 0 ) a) 800 2 a 1,040 ) ) 0 0) 0} 200 80 aeley si. 0s ) 0 0 ) 0) 0 0 400 is oe 0. 0. 0 0 0 ) 0 ) Mee 400 0 0) 0) 0. 0 0 400 Di eae 100) 800 0) 0) 800 0 0 0) Ze eae 100 100 0 0 100 0 0 100 BeBe 2 40 0) 0) 0) 0) 0 0) 40 Te 400 | 0 0 0) 0 ) 0) 1,200 iC Sen 400 40 200 ty) 240 0 0 400 DG ev. 2 800 0 _ 400 0) 400 0) 0 1,200 | peese2 1,200 | 0 0) 0 0 0 0 0 OL ean 8,400 0 | 800 0 $00 0 0 0) toner. 5,600 0 800 ) 800 ) ) 800 De ee 14,400 0| 2,400 0 2,400 800 0) 4,800 Ors . 12,000 ) 0 0 0 0 Gases 22,400 0} 5,600 0 5,600 ) ) 800 2 eae 3,000 0 500 0 500 0 0 ) DOS 5,500 0 0 0 0 0 0 500 Dies ho 32,000 ) 0) 0 0 0 0 1,600 / | | i ae 500. 0) 0 0 0 0) 0 500 Mites es.) Oo Oo 0 0] 0 ) 0 500 fe 500 0 0 0) 0 ) 0 540 Dee a. | 4,500 0 0 om 0 0) ) 500 (Ise ) 0 0 0 ) 0 0 2,000 stereo 120 0 0 0 0 0 0) 2,000 iS a iaeie 1,200 | 0 0 ) ) 0 ) 1,000 ae 2,400) ) 0) 0 0 0 0 2,000 De ee 1,500 0 0 ) 0 0 0 500 | nee 860 0) 0) 100 100 ty) 0 0 iC an 10,600 0) 0 600 600 0) 0 0 DOs, | 1,800 | fy) 0 40 | 40 0 0 0 eet os 100. 0| 0) 240 | 240 | 80 | 0) 1,621 ' | ‘Average...... | 25,974, 18| 206 244 468 56; 4 1,685 334 TABLE I—continued. ORGANISMS PER CuBIc METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries init are based on filter-paper collections.) : 8 S nS) 8 Polyartha platyptera Ss 8 8 3S. e8 &§ Male eggs 1898 S8 SS = Ss oss sa a8 Sie las Moos) | oes Se iB eS S 2 5 & B38 S ree arried - = = = = Z ny a Jane Alas aes 0 0 0 0 0 1,000 0 0 iy ge Billite cies oes 10) 0 0) 100 0 1,200 0 0 aie 45 eect sa kp 10) 10) 10) 0 (0) 11,997 0) 0 IM eu cso 0 10) (0) 0 24 3,200 (0) 0 rer te etterce ie 0 0) 0) (0) 240 2,000 0 0 Oo ON a ee 0) 0) (0) 0) 80 1,600 0 0 SMD oe er 0) 10) 0 0 0 6,318 0 (0) Masry cde case santos 400 0 0; 0 800 3,200 (0) 0 OY RE Re 0 0 0 0| 1,200 5/200 0 0 Se SNS ee 0 0 0 0| 6,400 22/200 0 0 oT ND DP sae 0} 400 0) 0} 10,800 37,600 0 1,600 iG cD Oana netys 0 0 0 0) 200 40,400 0) 2,600 Apria eo ycena te 0 0 100 (0) 300 42 ,800 1,300 2,800 See ual Deiat ae 0) 100 100 0) 0 26,700 900 1,900 pemel Oie cera 10) 400 400 0 0 148 ,200 8,800 1,600 eee Ole star 0) (0) 0 0 0 696,000 150,400 53,800 WES?) Ss Sa 6 el 0 0 10) 0 0 582 ,400 y 0 19,200 eer Li OKs sacs (0) 0 0 0 10) 137,600 4,800 Uprele te. 0 800 0 10) 0 195,200 12,000 2,400 ae A hae ie 0) 0) 200 800 10} 52,200 ; (0) 10) Pe aS 1S Wetter Ne 0 (0) 200 400 0 52,400 200 0 fibboXSern eerie otc (0) 0 0 0 0 304,000 1,600 10) ratte TARE Ne Mier 0 0 10) 10) 10) 432,800 0) 0 Ba ae eseey Oe ies 19,200 800 0) 0 10) 241,600 0 0 bee AAS einer tent 11,200 800 0 0 0 56,800 (0) c Nialivanueo ee ae 2,000 0 0 0 0 6,400 0 0 fay peleohe eee che 1,600 0 (0) 0 10) 21,600 (0) 0 RipawlOlx eres ane 7,200 0 800 0 0 89,200 0 0 Tp AN Sh eae ke 4,000 m0) 800 (0) 0 86,400 0 0 ANigan 2k cy eine 15,200 0 0 0 0 288 ,000 0 0 AOE en 4/000 0 0 0 0 55,200 0 0 Ls Sel Gletceen ate 5,600 0 0 10) 0 84,800 10) 0 CO iene He! 57600 0 0 0 0 96/000 0 0 dee ORG E se; 800 0 0 (0) 0 51,200 (0) 0 Sion. Osaeecs (6) (0) 0 0 (0) 4,000 0 0 GNC e a 2,500 0 0 0 0 31,000 “<0 0 Be Oya a hee 1/500 0 0} 500 0 72/500 0 0 BS RAD Tete bee 4,800 0) 0 0 10) 238,400 0) 1,600 Octo deose rat 1,000 0 0 0 0 24,500 0 oO Se hd lies ye SP 0 0 0 10) 0 47,500 5,000 500 ae malts arey etal 0 10) 10) 0 0 27,000 2,000 1,500 DMO Siaeatern ian 0 0 0 0 10) 37,500 0 2,000 Novas bila eae 60 0 0 9{0) 0 500 0 0 oe toedere eit (0) 0 10) 0 0 1,000 0 0 mage a US sane oe 0 0 (0) 0 0 2,000 10) 0 PDD et meee 400 0 0 0 (0) 6,000 (0) 0 pote DO cane 0 0 10) 0 10) 1,000 0 0 ID ECHGH eres 0 0 0 0 0) 6,020 |, 0 160 ccna Qraaeley age 0 10) 0 0 0 42,100 100 100 ne Ne 2 Oh gee 0 200 (0) 0 40 63,400 0 200 mee Ay hater tata 0 0 (0) (0) 0 19,200 0 0 | | | ASU TENEO 6 ae 6 1,674, 67 | 50) 37 388 | 86,674 | 3,598 1,768 ! | i} i 335 TABLE I—continued. ORGANISMS PER CuBiIc METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) = Polyarthra S$ a platyptera sf 2S 8 o WS Winter eggs se 8 ES 3:8 83 S ors 1898 S a 33 = ae uz als} & ts She AES zs 88 RSS = 8 ae 23 8 ss | 82/88 | 88 25 S55 i Sho SS, Ss Sas) ES Rips Bl Free |Carried < = e e ee a? & Yn Mere Wt 0 0) 2,200 ) 0) 0) 0) 2,120 100 SEZ eee 100 0 1,000 (0) 100 0) (0) 300 0 MLO cic ss 0 0 Se2i7 0 0 0 0 4,257 0 halt, (Cleeeeee 0 0 1,700 0 0 0 72 1,000 0 a Blo eCere ts» 0 10) 2,800 0 0 0 0 1,200 0 CO oa ese naretes 800 0 3,200 (0) 400 0 0 800 1,200 eee 0 0 6,318 (0) (0) 0 632 0 0 i 2g et 0 0 3,200 10) 0 0 0 6,400 0 a ete ens 0 0 4,000 0 0 (0) 16) 4,800 0 2 Ol aie 200 0 17,800 0 40 0) 0, 15,200 160 a 0 0 26,400 0 400 10) 0 58,000 0 eee 200 0 11,400 10) 100 0 10} 47 ,000 (0) oie eee 100 100 10,400 0 300 (0) 0 21,000 0 mL Dtors Een, 3 0 100 8,700 10) 200 6) 0 11,500 0 lea 1,600 10) 104,200 (0) 0 0 400 368 ,000 0 “2 er 22,400 0 502 ,400 0 (0) 0 1,600 954,400 6,400 iene Se Sears 51,200 0 316,800 0 0 0 0 1,139,000 9,600 mee OlSs.c.5,.. 11,200 0 72,000 0) 3,200 0 0 233,600 6,400 S" chereaaene 2,400 10) 120,000 0 0 0 800 206 , 400 800 OAS. chess, 400 0 28,800 200 0 0 200 60,480 0 eri ershica sc 400 0 10,600 40 200 0 600 61,600 0 BPI 7 sch ds 0 10) 96,000 | 1,600 0 0 3,200 48 ,000 0 2 ees 800 0 119,200 (0) 0 0 800 19 ,200 800 MED Lee cers ic! 3 800 10) 154,400 0 10) 0 | 112,000 795,200 3,200 1 Oe 800 0 16,000 100 0 (0) 0 22,400 | 0 MALU Disa lc cle 400 0 7,200 0 40 0 800 22,800 400 0 ee 400 (6) 13,600 (0) 400 0 400 9,600 800 So SO Rae 800 0 24,000 (0) 0 0| 20,800 64,800 0 (2 es (0) 0 53,600 10) 10) 10) 400 8,000 0 EA 0 0 295,200 10) 800 800} 12,000 170,400 0 i Oe stat ace 800 0 84,800 0 400 0 4,800 52,000 800 ed Ole eh c's. 0 0 108 ,000 0 800 (0) 1,600 18,400 60 (OG) ee eee 0 0) 63,200 0 800 0 3,200 24,800 0 06S era 800 0) 47,200 0| 1,600 800 800 1,600 10) BEDb. Oe. sss 0 0) 8,800 0 0 800 0 0 0) OO Eee 1,000 0 20,000 (0) 0 0 1,000 14,000 500 pemerD Olers.s.or., « 1,000 10) 103 ,000 0 10) 0 4,500 27,000 500 MEL Pellccey. 1,600, 1,600 86,400 0 0 0} 30,400 | 265,600 100 (Oe ae: 1,000 0 15,000 0} 1,000 10) 500 5,000 0 7 ee eee 0 0 5,500 0 0 0 0 27,000 0 Mel Sissy 2.2% 0 0 14,000 0 0 0 500 77,000 10) ee D OSs cies 0 0 17,000 0 0) 0 0 824,500 0 Mea elke na; tere: ds 500 0) 4,500 (0) (0) 0 0 110,500 (0) a" ee 1,000 0 2,000 0 ) 0 0 97,000 60 ILO. ices a 1,000 0 2,000 0 10} 0 0 | 110,000 0 Se 0 0 6,000 0 0 0 0 | 38,000 0 11 Do) ee 0 0 3,000 0 0 0 500 | 39,000 0 Wee 6). 00.3 10) 0 9,160 0 0 0 20 42 ,500 0 ReneS iets (0) 0 29,300 0 0 10) 2,500 55,720 0 pean Ore & crane 0 0 52,000 0 | 0 0 0 59 ,200 | 0 Uy 10) 0 11,000 0 0 (0) 400 17,640 0 | | Average...... 1,994 34 52,560 37 46 3,950 | 120,391 611 207 TA BIE 336 I—continued. ORGANISMS PER CuBiIc METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries init are based on filter-paper collections.) 8 & = is} 8 ns aay dos ss 38 ee 2 3 S 1898 Be So RSS as s 8 8 — S R Qo + to Ss af ak es! g5 Ss S855 ss g5 88 s& io) aR Ss oO S o) {o) fe) a BH & ay a a a Jane Wider: 500 0 0 0 700 0 100 ieee 200 0 0 0 1,380 0 440 Ey Nate 6,579 0 0) ) 4,788 ) 462 Bebo © oy ateee 300 0 0 0 216 0 24 Gish eet altel! 400 0 0 0 320 0 0 SE AOS 5,600 0 0 ) 1,200 80 0 SRE D i ek 0 0 ) 0 3,285 ) ) Marsenieieeee 1,200 80 ty) ) 804 ty) 160 ea Seige 800 0) 0 ) 3,080 40 80 ede Kp ial 3,960 0 ) 0 12,880 40 560 EDO ee 4,000 40 40 ) 19,440] 320 800 OB EDO 3,200 100 0 0 22.180] 160 360 Nore Oh aoee 1,100 | 300 200 0 34,560| 200 360 BEAD, ne ta 1,000 200 100 0) 28,060| 320 320 Ser One pees 84,000 400 0) 0 34,200} 200 400 DG ieee 38,400 3,200 0 0 56,800, 800 1,920 MERZ Bocacut 278,400 9,600 0 0 204,800 ty) 2,800 a MOn aan 91,600 38,400 0 0 235,400] 400 5,600 Lines fae ea 56,800 17,600 | 3,200 0 182,300| 1,600 8,500 7) eis 9/400 600} '200 0) 167,080} 400 24,080 a Ipeneae e 12,000 1,000 0 ) 162,800} 440 51,480 urnew ieee 11,200 200 0 0 438,800] 1,600 136,000 SN ceca 13,600 0 0 ) 211,400] 400 29,200 Ben OED AO cael 257,600 800 0 100 83,100} 200 2/300 ESS Dees 51,200 800 0 500 45/600} 400 10,100 ipeth? Ba ceade 47,200 400 | 0) 1,600 4,920| 440 640 GES st Dine Bel ta 16,800 1,600) 400 1/200 1,620 60 360 cero Manauele 34/3800 4'000 0 9,200 14,040 0 1,240 SD G vee oe 4/800 28/000 1,600 99/600 23,000 0) 9,960 Angsana 178,400 18,400 | 1,600 30,400 22,160 40 10,520 tO Par aes 20,000 4/400 | 1,200 4,000 4: 120 0 1,080 coal eee 10,460 3,200 0 22,400 4;500| 800 1,320 Lag its sols 35,200 4/000 0 17,600 17,340] 180 1,820 CaO eae 7,200 6,400 | 0 14,400 27,080 0 4/040 Sept moraunee 0 0) 0 0 9,080 ) 720 NAN tein 9,500 1,000 0 5,000 24720) 500 3,420 SEH BNO oh is 17,500 500 0 5/500 21,880 0) 1,560 SON eee 38,500 14,400 | 3,200 19/200 99; 300 0 1,100 Octane 0 1,500| 500 2,000 33,880 0) 1,320 re wa Filiaen 2,000 0) 0 2.000 34,060 ) 2,000 ORR AN a} 10,500 1,500) 500 500 25,640 0 2'120 RO teeta tea 78,000 500 0 0 26,020 0 1,020 Nove eae 29,000 0 | 0 60 8,600 0) 120 Cie Sian A 41,060 0) 0) 0 15,080 ) 0 Saige Imire ca A 60,000 0 | 0 ) 13,100 ) 100° OO eee 66,000 0 0 0 13,920| 320 2,800 Sir DON Re 500 500} 500 ) 6,180 0 80 Decwiorec ae 0) 0 0 0) 9,740 0 260 ce havea 800 0 ) 0 21,740 | 0) 240 Cae 1a) maces i 2,600 0 0 0) 2/440 0 400 SE ONE 400 40 0 0 6,800 0 280 Average...... 31,620 3,147 255 4,524 47,042 191 6,241 a oo eooo0 o0000 COCO00 C000 C0000 C000 36 TABLE I—continued. ORGANISMS PER CuBIC METER IN PLANKTON oF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) 337 — g S < 's % s§ 3 = as is] ok gs Se Pon se | ee, ES) oe ‘E& BS SS Ss as S'S gk a cop ee ee | Be) Bs [ose § S S g 8 q” = 0 0) 100 0) 0) 0 0 0 0 200 0 0 0 0 308 0) 0 0 ) ty) 0 24 0 0) 0 0 0 0 0 0) 0 0 0 0 0 0 0) 0 0 0 0) 0 0 0 0) 0 0 (0) 0 380 0 80 ) ) 0 0 40 ) 40 0 0 ) 0 120 ) 440 0 1 0 0) 0 280 ) 480 0 0) 0 0 20 20 240 20 0) 0 0 100 40 200 0 0 0 i) 60 20 200 20 ) 0) 0 100 0 0 0 0) 0) 0 300 320 800 0 0 0) 0 2,800 ) 0 0 0 0 0 3,600 400 600} 600 0) 0 0 3,500 400 3,300) 300 0) 0) 0 5,920 2,960 7.,880| 440 160 0) 0 33,920 8,720 5,040 1,000 720 40 a) 62,800 55,800 600 | 3,400 11,600 0 0) 6,000 10,600 200} 2,400 9,200 0 0) 1,500 400 0 100 ) 0 200 700 0) 0) 0 0) 0 100 200 0) 40 0) 0 0) 400 180 0 0 0 0 60 120 0) 0) 160 0 0 40 1,040 180 120 ) 0 0| 8,580 1,080 40 ) 0 0 0| 6,960 3,520 0 0 ) 0 0 360 360 0 0 ) 0 0) 60 1,260 0) 0 0 0 0| 1,020 900 0) 40 0) 0 Oily 22520 1,440 0) 40 0 0) 0 240 440 0 0 60 0 0} 1,800 1,560 60 0 60 0) 0 960 480 0 100 0 ) 0 400 500 0 0) 40| 400 0) 880 120 920 a) 0} 600 0 400 40 1,360 0 80 10) 0 560 0 340 0) 120 60 ) 0 ) 60 0. 60 0 0 0) 0 0) 0) 0) 0 0 0) 0) 100 0 ) 0 0 0 0 0) 0 0 0 oO. 0 0 ) 0 80 0 0 0 0 40 20 200 0 oa 0 0 140 40 220 0) 0 0 0 120 ) 160 0) 0 0 0 0) 0) 280 0 0 0 0 2,441 1,539 422 181 417 479 261 338 TABLE I—continued. ORGANISMS PER CuBic METER IN PLANKTON OF ILLINOIS RIVER IN 1898 (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) a” a < 2 : x ay aS . 8 is} as 1898 R : 2 = = a + _s 8 gS Ro &., gS | £22 R28 a ae SS QS 38 Sie | S&S 228 68 5 a S3 SS 3: | SS | Sea ee & S S S S S S S en a ee ae 600 0 0 160 0 0 0 9 Ce ihaes Uae 940 40 0 160 0 0 0 40 SB EA es 4,326 77 0 308 0 0 0 308 Reba “Sh ae 192 0 0 48 0 0 0 0 cae Rs 320 0 0 160 0 0 0 0 ep eS apaet 1,120 0 0 80 0 0 80 0 Tied ie 37285 0 0 0 0 0 0 0 Mart, wet wie 644 0 0 0 0 0 0 0 Dee 2,960 40 Ol 120 0 0 0 0 eosin eteseny: 12/280 40 0 400 0 0 80 120 CSN 18/320 200 0 80 0 0 0 80 eee aa 21/660 100 20 60 0 0 20 0 Np SS acer: 34,000 200 20 40 0 0 0 0 ORT ae 27,420 1,120 0 0 0 0 0 40 Gig io nigtne 33,600 0 200 200 0 0 0 500 Cp eneee 54/080 0 1,600) -2,880 0 0 0 4,160 May) Soiae 202,000 400 0} 8,000 400 0 0 1,200 SOA Os aee 229,400 0 600| 5,200 0 0 600 2/200 GST Da eae 172,200 800 200 600 0 0 0 3/300 Racy aia 142600 80 920 320 0 0| 1,080 1,640 Suse aes 110880 0 200 0 80 0 400 640 une woe ae 301,200 0 400 0 0 0| 2,600 4,000 St a! 181,800 0 200 0 200 0 800 4/400 eGo p reall 80,600 0 0 0 0 0 0 400 ere ee 35,100 0 0 0 0 0 0 200 Tialiy so easton 3,840 0 0 0 0 0 0 120 EAD ase 1,200 0 0 0 0 0 0 180 LCT. 12800 0 0 0 40 0 40 240 eae 137040 0 0 0 120 0 120 300 Auoy $2. Sere 11,600 0 0 0 0 0 0 40 PRI SB So! 3040 0 0 0 80 0 0 160 Rea tae Was 2/380 0 0 0 0 0 0 180 Ue 3) dee 15,340 0 0 0 120 0 0 660 POR OLe ae 23/040 0 0 0 440 0 0 480 Septt cot een 8,360 0 40 0 80 0 0 0 ae CR ae 20/800 0 0 0 120 0 0 240 PESTO, Aa 20/320 0 0 0 120 0 60 360 bbe 3 Re 98/200 100 700 0 300 0 200 700 Oop” WA awe 32,560 0 120 0 320 0 200 400 Sette 32/060 0 200 0 80 0 0 120 Ce ates ke 23/520 0 280 0 0 0 40 40 SE Be 25/000 0 60 0 60 0 120 240 Now viene 8,480 0 120 0 0 0 0 60 ME RT athe 15080 0 0 0 0 0 0 120 apse 13,000 200 0 200 0 0 0 0 UD Be in| 107880 480 0 | 80 0 0 0 160 ca Oat ok Ni oeeaiG0 80 0 4 pn aC 0 0 Deed vor wees 9,480 20 0 | 0 0 0 20 0 Tye eee 21,500 0 0 40 o| 40 0 0 BE TN ie 27040 40 0 160 Glas ae 0 0 BOOT a es 6/520 0 0 120 o| 40 0 0 Average...... 40,609 78 | 113 373 49 2 124 539 i ‘ . 339 TABLE I—continued. ORGANISMS PER CuBiIc METER IN PLANKTON OF ILLINOIS RIVER IN 1908. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) oooo ooo oooo o°o°o°o°o - e 2 g 2 S Se se uo 8 Oi S 3 8 < = 1898 ae aa s8 S83 38 3 3 2a 35 ae | ee | se. | Se | B82 | #2 | Ss Aa iS Sk =< = oS $0 Sa 8 8 q Soaps Wer ieee |S : 120 240 40 0 0 0 0 ‘ 200 - 500 0 0 0| 4,700 0 770 2,709 0 0 0 774 77 72 72 0 0 0 24 100 80 80 0 0 0 80 0 160 800 0 0 0 400 0 126 3,159 0 0 0 0 126 eter... 4 640 0 0 0 0 4 Bian. 800 2,000 0 0 0 400 0 ae... 220 11/200 40 40 0] , 600 0 maeet 1,120 16/800 40 0 0 40 40 Beh ea. 760 20/700 0 0 0 40 20 ae 1,420 32,300 20 0 0 0 40 eee... 1,100 25/100 60 0 0 40 40 a 57500 27/200 0 0 0 100 100 Bee. : 24/320 20/800 0 0 320 a 19,600 182,400 0 0 0 0 0 a0... 53/200 169/600 0 0 0 0 200 an 27/900 166/400 0 0 900} 4,800 200 in 12/160 126/400 0 0 840 40 80 i 5/680 103/800 0 0 160 40 80 De... 23,800 270,400 0 0 0 0 200 ae. 11,400 164/800 0 0 0 200 0 ie 14600 65,600 0 0 0 0 0 ce. 47500 30/400 0 0 0 300 100 SSE. 5... 1,320 2,400 0 0 0 0 40 ee 780 180 0 60 0 0 180 1. 1,680 10,800 0 60 0 0 80 pa... 840 11,600 0 0 0 0 0 peeee So... 360 11,200 0 0 80 0 40 Bi 400 2400 0 0 0 0 0 fees. 600 1/600 0 0 0 60 60 ae: 3,360 11,200 0 0 60 60 180 Bee... 57520 13600 0 0 0 0 120 a 240 8,000 0 0 0 40 160 Be os 4,320 16,000 60 0 0 120 180 POr ics: 19,000 0 60 0 120 60 iy 0 96/000 0 200 0 300 400 ae 2,600 29,000 0 0 0 0 80 aes... 3/920 27/500 0 80 0 40 40 Mies 51580 17/500 40 40 0 40 40 ee 2/400 22/000; 120 0 0 120 60 aa 300 8,000 0 0 0 0 180 as... 960 14/000 0 0 0 120 120 tse. 400 12000| 100 0 0 100 100 Lie 160 10/000 0 0 0| 2,000 320 ae, 4 6/000 12 0 0 0 120 nee: 440 9,000 0 0 0 500 0 ays 1,060 30,300 60 0 0 0 0 oe aaa 1/800 0 20 0 0 0 37. 920 5,400 0 0 0 20 0 4 Average......|. 4,780 36,707 11 10 39 318 76 124 b> (23) 340 TABLE I—concluded. ORGANISMS PER CuBIc METER IN PLANKTON OF ILLINOIS RIVER IN 1898. (An asterisk at head of column indicates that all entries in it are based on filter-paper collections.) z = = g 8 < 2 32 8 = 8 4 S i eee g s S 3 £ ies Ses eC. [Piers 3 a 8 a EES Mah Seen ae ce ee ga 5 a8 = 1S) Sia Jo) os oS oN OA a Sy G = a G G | Tanti ian | 0 0 20 1,220) 544,201,080| 1,042,720| 545,243,800 reo pee | 0 80 40 7/720 | 2021136/180 288,340) 202/424°520 Oe Tein 0 0 154 7,738 | 180,295,247 195'484| 180/490,731 Reba eouehee 0 0 24 648 | 619,030,830] 1,381,960] 620,412,790 Sa EGU e 0 0 80 2,160 | 297;341,760 651,200| 2791992'960 ica AG oe tke 0 0 0 6,000 | 653,122,000} 1,091/920| 654/213/920 bas Ue 0 0 0 35285 | 115,514,812 715;697| 116/230/509 Marty drs. ate. 0 800 160 1,124| 21,790,800) 1,809,688] 23,600,488 Fe ig Cecchi 0 40 40 3'360| 96,590,840 542'680| 97'133/520 cmaeiey aay 0 40 40 3,280 | 118,382,400 453'100| 1181835,500 ce OT Lela 0] 1,640 0 1/600 | 127/930/360 484'760| 1281451'120 TRIO N Eee 0. 80 0 2'020| 53,463,040 444'900| 531907/940 | Noicy Eero: 0 900 | 100 1,860| 42,470,860 363,980| 42,834,834 eT see 0 220 | 20 980| 905934/320| 1,432,400| 102/366/720 ios RK ee 0 400 | 0 3,100 | 927,956,220| 2/134'800| 930:091,020 CHE Yale 0 pola wo. 0 20/160 |3,872,537,280| 16,092/840 | 3,848,630,120 May 1Scn. 0 0 0 10,800 |3,200,166,960| 898,919,800 | 4,099 086,760 co edna 0 0 200 131600 |4'4671165,760| 42/826;200 | 41509'991'960 Neil aan a 0 100 0} 213/900 |2'148'960,400) 31/091;900 | 2:180}052;300 LEAD ae em 0| 1,200 0 5/360 | '190/671,160| 4;,969'580| '195'640/740 Ce ea pee 120 100 0 4,720 | 252;704,250| 2/772;/200| 255,476,450 lfeclon Ups nk 200 0 0 24,000} 259,129,000} 9,695,000] 268,824,000 CER TV bet Oo} 0 0 4400 |1,149'333,480| 10/959/400 | 1,160,292'880 CS GH see) 300 0) 0 31300 | '641/056,900| 155159;600| '656,216,500 ci Ge teed at 200 Ol) 300 10,900 | 612/686;240| 7;796;700| 620;482;940 Tila eens 40 0 120 5,800 | 257,668,840| 495,337,320| 753,000,160 Citi OF ee ve 120 60 120 5/320| 2231936,000| 4/135,160| 228,071,220 to OMI: 40 80 0 21680 |1,578,635,720| 1,717,240| 1,580,352 ,960 Ya ie 0 60 0 1/440 | '281/604;120 907;240| '282/511/360 Acre be eee 0 0 0 3,440| 369,169,240] 5,833,440| 375,002,680 RNC aie 0! 0 0 840 |3,084/000/880| 693874760 | 3,153,875 ,640 Cn Var Ya 0 0. 0 6,580 | 583,940'376| 1/240/920| '585/181,296 TONE a8 60 0 0 81420 | 544,041,260| 1/519,140| 545'560,400 ko aoa nd 160 80 0 5/320 | 797,312,600 597,880| 797,910,480 Sept. 6...... 0 0 0 4,320| 488,146,040| 60,463,480) 548,609,520 cng: se 60 60 0 2'420| 676,773,060| 1/712,720| 678485, 780 7 Oem 180 0 0 5'920| 330,837,120| 32/466,660| 363,303,780 CMTS ot FR) 0 0) 0 12/100} 511,099/300} 3/201;200) 514,300,500 Octane 40 40 0 2,740| 264,225,400] 2,035,720| 266,261,120 iat eee 0 0 0 1/240| 126/398/510| 1,495,880| 127,894,390 CR aaa 0 0 400 17140] 182/891/160| 1,967,020| 184/858,180 eee) g a eee 0 0 0 31860 | 218,768'810| 2/453,060| 221,221,870 Nowe seledes 0 120 60 4,360| 209,418,675| 1,189,380] 210,608,055 avg wane 0 0 0 15/300| 277,953'180| 1,281,220] 279,234,400 E15) as oe 0 0 100 7/500) 407:573,600 732,300| 408/305,900 ao pine ae 400 0 0 25,680 | 466,411,780| 1,109,040] 467,520,820 SISA) 0 80 240 1/900 | 364/032;900 7991980| 364/832;880. Weer neneeen 0 0 180 680 | 529,250,270 916,780) 530,167,050 as chet Wek 0 500 60 1,560 /1,715.442/415| 1,757,440| 1,717,199,855 CONOR eo 0 0 80 320 | 848'243/820 682/440) '8481926,260 CaO a ig a 0 0 80 340 | 387,414,000 548,700} 387,926,700 Average...... 37 135 52 9,393 | 723,283,871 | 34,226,468 | 756,548,801 BIBLIOGRAPHY. Amberg, C. 00. Beitrage zur Biologie des Katzensees. Inaug. Diss. 78 pp., 5 Taf. Zurich. Also in Vierteljahrsschr. d. naturf. Ges. Zurich, Jahrg. 45, pp. 59-136. Asper, G., und Heuscher, J. 85. Zur Naturgeschichte der Alpenseen. Jahresber. St. Gall. Naturwiss. Ges., 1885-86. 43 pp. Apstein, C. 96. Das Stisswasserplankton. Methode und Resultate der quanti- tativen Untersuchung. Mit 113 Abbildungen. 200 pp., 5 Tab. Kiel und Leipzig. Bertram, [A.] 92. Beitrage zur Kenntniss der Sarcosporidien nebst einem Anhange tiber parasitische Schlauche in der Leibeshéhle von Rotatorien. Zool. Jahrb., Abth. f. Anat. u. Ont., Bd. V., pp. 581-604. Birge, E. A. 01. List of Crustacea Cladocera from Madison, Wisconsin. Trans. - Wis. Acad., Vol. VIIL., pp. 379-398, Pl. 13. 94. A Report on a Collection of Cladocera, mostly from Lake St. Clair, Michigan. Bull. Mich. Fish Comm., No. 4, pp. 45-49. 1 table. "95. Plankton Studies on Lake Mendota. I. The Vertical Dis- tribution of the Pelagic Crustacea during July, 1894. Trans. Wis. Acad. Sci., Arts, and Letters, Vol. X., pp. 421-484, PI. VII-X. 97. Plankton Studies on Lake Mendota. II. The Crustacea of the Plankton from July, 1894, to December, 1896. Trans. Wis. Acad. Sci., Arts, and Letters, Vol. XI., pp. 274-448, Pl. XV.—XLII. Borge, O. 700. Schwedisches Siisswasserplankton. Botaniska Notiser, 1900, pp. 1—26, Taf..1. 341 342 Brewer, A. D. “98. A Study of the Copepoda found in the Vicinity of Lincoln, Nebraska. Journ. Cin. Soc. Nat. Hist., Vol. XIX., pp. 119-138, Pi vale Brunnthaler, Josef. 00. Plankton-Studien. I. Das Phytoplankton des Donaustromes bei Wien. Verhandl. d. k. k. zool.-botan. Ges. Wien, Jahrg. 1900; Baile pps 308311: 01. Die Coloniebildenden Dzinobryon-Arten. (Subgenus Eudino- bryon Lauterborn.) Verhandl. d. k. k. zool.-botan. Ges. Wien, Jahre. 1901, Bd. LI., pp. 293-306. Mit -5 Fig. im Text: Butschli, O. °80—’89. Protozoa. Bronn’s Klassen und Ordnungen des Thier- reich, Bd. 1., Abth. I-III]. 2035 pp., 79 Taf. Wetpzigaeue Heidelberg. Burckhardt, G. 00. Faunistische und systematische Studien tber das Zooplankton der grésseren Seen der Schweiz und ihrer Grenzgebiete. Rev. Suisse de Zoologie, T. VII., pp. 353-713, Pl. 19-22. 00a. Quantitative Studien tber das Zooplankton des Vierwald- stattersees. ~Mitteil. d. naturf. Ges. Luzern, 1900; Heft 3) pee 129-439; Separatabdruck, 311 pp. lenbhngiullle he |. 02. Report of the University of Illinois. 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Das Potamoplankton der Wolga bei Saratow. Zool. Anz., Bd. XXIII., pp. 625-627. 03. Report on the Fauna of the Volga and the Aquatic Fauna of the Government of Saratoff. Bull. Soc. Naturalists of Moscow, 1903, pp. 1-148, Pl. 1:, Il. (Russian.) EXPLANATION OF PLATES. iPrArE 1 Seasonal distribution of synthetic groups of planktonts, Chlorophycee, Bacillariacee, and Mastigophora, from July 1, 1895, to October 1, 1896. Note changes of scale indicated at bottom of diagram. Numbers in column at left apply only to 1895. In this plate and in II. and IV., apices exceeding the limit of the diagram are dropped down between dotted lines to show location. Circles at bottom indicate location of day of full moon. Piano 1G The same as above, from July 1, 1897, to April 1, 1899. Note change in scale from previous plate. Prate IIL. Seasonal distribution of total Rotifera and Crustacea from July 1, 1895, to October 1, 1896. The Crustacea included, belong almost exclusively to the Ento- mostraca. Apices exceeding the limits of the diagram are dropped down between dotted lines to show location. Totals include both adult and immature stages of the Entomostraca when detached from parent, and both free and attached eggs of the Rotifera. PraTE IV. The same as above, from July 1, 1897, to April 1, 1899. PLATE V. Seasonal distribution of Polyarthra platyptera. Total number of individuals, not including eggs, represented by ordinants, parts of which exceeding 200,000 are represented by diagonal lines instead of solid vertical lines. Thus parts of a seasonal plot which overlap those above it on the plate are represented by the diagonally-lined ordinants. 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GE lpob' oc MdiEeVZ Bel Seems a vie} | DAY }ADh}o-| JO woINgIW4SIC] yeUosoaS 00008 (000 OS) 000 0° 000 0S! 000 0¢ 0000S! 000'0S 0000S) ERRATA AND ADDENDA. Page 58, line 7, for ovalis read ovata. Page 85, line 8, for longicaudus read longicauda, and just above Phacus pleuro- nectes read the following paragraph :— Phacus longicauda var. torta, n. var.—This variety, for which I propose the name ftorta because of the twisted body, is figured by Stein (’78, Taf. 20, Fig. 3). It occurred sparingly in midsummer from July to September, rarely in October, in 1896 and 1897. Page 91, line 18, after T. caudata Ehrb. read T. lagenella Stein. Pages}153, line 3 from = bottom, 168, line 16, and 178, line 14, for ’98 read ’98a. Pages 156, line 11, 159, line 16, and 161, line 5 from bottom, for ’93 read ’98a. 361 BULLETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL HISTORY UrBana, ILuinois, U. S. A. Wow. VIII. | Lee 1908 me Arricre IT, NEW GENERA AND SPECIES OF ILLINOIS THYSANOPTERA BY J. DOUGLAS HOOD AE oe rSy i Rect we ARTICLE I].—New Genera and Species of Illinois Thysanoptera. By J. Doucias Hoop. In the present paper, descriptions are given of five new genera and fifteen new species of Illinois Thysanoptera. For much of the material upon which these descriptions are based, I am indebted to several of my friends and associates, among whom may be mentioned Charles A. Hart, Robert D. and Hugh Glasgow, John J. Davis, Lindley M. Smith, Henry E. Ewing, James Zetek, Frank C. Gates, and George H. Coons. In the measurements, non-chitinous portions have been excluded. For example, the length of the prothorax is taken to be its length along the median dorsal line, exclusive of the membrane connecting it with the head. Type specimens are in the writer’s collection, and in the collection of the Illinois State Laboratory of Natural History. SUBORDER TEREBRANTIA Hatipay Famity THRIPIDA! Uzel. HETEROTHRIPS gen. nov. (Fig. 1.) (repos, other than usual; Oped, thrips.) Head wider than long. Ocelli present. Antenne clearly nine-segmented; segments 3 and 4 conical, large, their combined lengths about equal to that of segments 5—9, each with an apical band enclos- ing small circular sensoria (?), disposed in two nearly regular transverse rows; segments 5-9 much nar- rower than 3 and 4, successively diminishing in diameter; segments 5-8 provided each with either one or two slender sense cones. Maxillary palpi three-segmented. Prothorax twice as long as head, sides decidedly arcuate; not armed with long spines. Second fore tarsal segment armed with a claw- med like appendage. Fore wings long, narrow, pointed, iciercinree. abe. with two longitudinal veins, separate for their female. a, left anten- : $ na, dorsal view; b, entire length, and set with from 20 to 24 stout right fore tarsus, out- spines; costa similarly armed with stout spines which Fa ge Oars 361 362 gradually increase in length toward apex of wing. Sides of abdomen reticulate, sparsely spinose; posterior margins of abdominal segments 2-8 prolonged into small equidistant flattened spines (excepting: under the wings), which may be united at their bases into plates; tip of abdo- men (in female) conical, tenth segment weakly chitinized in its apical median half; ovipositor well developed, curved downwards. This genus, although seemingly a specialized one and suggest- ing Sericothrips Haliday, has retained certain primitive characters (the nine-segmented antennz, the character of the sensoria, and the tarsal appendage) which indicate affinities with the Aolothripide. In view of the fact that in all the species of the order, a change in the number of antennal segments always consists in a reduction and never in an increase in the number of these segments, it might be assumed that the Thripide early divided into two branches, one of which, continuing more nearly along the original line, gave rise to the present genus, while the other produced the ordinary type of Thrip- ide. Heterothrips is, indeed, so sharply separated from all other members of its family, that a new sub-family might easily be erected for 1t; but it seems best to defer this until the Thripidez are better known. Heterothrips arisem@ sp. nov. (Fig. 1.) Female.--Length about 1.25 mm. Color nearly uniform dark blackish brown; tarsi, anterior tibiz, and third antennal segment pale yellowish. Head rather coarsely transversely striate, faintly but sharply con- stricted at posterior margin of eyes; frons acutely emarginate. Antennal segments 1 and 2 slightly lighter than body, shaded laterally with black, the former provided with a sub-transverse carina; segment 3 pale yellow- ish, with a narrow sub-basal white band, and apical third clouded with brown; segments 4—9 uniform light blackish brown, excepting the yellow- ish sub-apical band of sensoria on segment 4. Prothorax about twice as long as head and two-thirds as long as wide; sides and angles rounded; surface sparsely spinose, and faintly reticulate. terothorax about 1.3 times as wide as prothorax, and about as long as wide; mesoscutum transversely striate, and with four pairs of short spines; metascutum concentrically striate. Wings just attaining tip of abdomen; basal third widened, the sub-basal width slightly more than twice the sub-apical, and contained in the total length about 7.6 times; color blackish brown, excepting a broad sub-basal white band. Legs reticulate; femora nearly concolorous with body, the anterior pair shading to yellow at apex; fore tibiz yellow, shaded later- 363 ally with brown; middle and hind tibize blackish brown, extremities paler; all tarsi clear yellow. Abdomen lanceolate, widest at segment 4; spines short, inconspic- uous. Measurements:—Total length 1.24 mm.; head, length .10 mm., width .18mm.; prothorax, length .16mm., width .24mm.; pterothorax, width .32 mm.; abdomen, width .34 mm. Antenne: 1,28 ym; 2, 42 n; eee; 4. 50; 5, 34 3 6,34 ps7, 25 pw; 8,22 W; 9, 25 uw; total, .37% mm. Male.—Length .72—.80 mm.; prothorax, length .14 mm., width .22 mm.; mesothorax, width .22 mm.; abdomen, width .19 mm. Brachypterous. Last ventral segment of abdomen with a broad, semicircular emargination, each side of which is an acute tooth. Described from twelve females and two males, taken at Urbana, Illinois, in flowers of Jack-in-the-pulpit (Arisema triphyllum), by Mr. Frank C. Gates. Genus SERICOTHRIPS Haliday, 1836. Sericothrips pulchellus sp. nov. Female.—Length about 1 mm. Color dark blackish brown to black, with bright red hypodermal pigmentation. Similar to S. variabilis (Beach), differing from it as follows: Head uniform gray-black. Antennal segments 1 and 2 dark blackish brown, the latter grayish yellow at middle; segments 3, 4, and 5 grayish yellow, 5 slightly clouded apically; segments 6-8 gray, the basal third of 6 grayish yellow. Prothorax concolorous with head, with conspicuous black reticula- tion, and thickly dotted with black spots, the latter visible only under high power. Pterothorax nearly concolorous with prothorax, the red pigmentation usually quite conspicuous. Fore wings black, tipped with white, and with two broad white cross bands, one near base, other near apex. Femora nearly concolorous with body, pale basally; groun color of tibiz pale yellow, the fore pair clouded basally and laterally with brown; middle and hind pairs pale at extreme base, beyond which they are concolorous with the femora to, or slightly beyond, middle; tarsi pale yellow. Abdomen often pale at middle, and with segments 7—10 darker. Measurements :—Total length 1.0 mm.; head, width .17 mm.; pro- thorax, length .14 mm., width .21 mm.; mesothorax, width .28 mm.; Bedomen, width .3l1mm. Antenne: 1, 22 4; 2, 39 mw; 3, 62 4; 4, 59 pB; Bere 0, 95 f0,.7, 11 #; 8, 14 #; total,—-31 mm: Male.—Length about .7 mm. Coloration similar to that of female. This species is very close to S. vartabilis (Beach), but the colora- tion is distinctive. In living specimens, examined under a hand lens, 364 the head and prothorax are velvety-black and without luster, due no doubt to the microscopic reticulation. At Muncie, Illinois (the only locality from which I have seen speci- mens) this species was very abundant upon the hop tree (Pielea tri- foliata). As many as fifty individuals were frequently observed on the under surface of a single leaf, where their peculiar coloration rendered them very conspicuous. SUBORDER TUBULIFERA Hatipay.* Famity PHL(@ZOTHRIPIDA Uczel. Genus ZYGOTHRIPS Uzel, 1895. Zygothrips longiceps sp. nov. (Fig. 2). Female.—Similar to Z. minutus Uzel, from which it differs as follows: a. Length about 1.1 mm. head about 1.1 times as long as wide, half as long as antenne, and about 1.4 times as long as tube. Anterior marginal spines on prothorax large, subequal in length to the others. Posterior margins of abdominal segments 3—7 provided each with two pairs of straight spines, the inner pair short. Tarsi light yellow, tibiz yellowish, the first and third pairs clouded at base, and the second pair at middle, with brown or black Z. minutus Uzel. aa. Length about 1.47 mm. Head about 1.4 times as long as wide, three-fifths as long as antennz, and almost twice as long as tube. Anterior marginal spines on prothorax wanting. Posterior mar- gins of abdominal segments 3-6 pro- vided each with two pairs of long spines, the inner pair sigmoid. Tibie and tarsi uniform bright yellow Z. longiceps sp. nov. The measurements of the female of this species are as follows: Total length Zygothrips longiceps, female, head and Ih aed) mim. , head, length paleys jaauanl. width prothorax. (J. D. H., del.) .134 mm.; prothorax, length 2123. mee width (including coxe) .232 mm.; ptero- thorax, width .234 mm.; abdomen, width .272 mm.; tube, length .102 *The division of the Tubulifera into the two families Phlewothripide and Idolothripide, proposed by R. S. Bagnall (Ann. and Mag. of Nat. Hist., Eighth Series, Vol. I., No. 4, p. 356; Apr., 1908), seems to be an unnatural one, apparently separating from each other species which are more closely related than the ex- tremes of the respective families into which they fall. Fic. 2 365 mm., width at base .057 mm., at apex .032 mm. Antenne: 1, 24 yu; 2,44 mw; 3,44 pw; 4,46 435,45 pw; 6,41 w; 7, 38 w; 8,24 mw; total, .30 mm. Described from a single brachypterous female taken by the writer in a gall on Solidago, at Carbondale, Illinois, June 20, 1907. LISSOTHRIPS gen. nov. (Accoos, smooth; Ooed, thrips.) Head slightly wider than long, sub-globose, narrowed posteriorly; eyes directed forwards; cheeks full, sparsely spinose. Antenne about twice as long as head, eight-segmented; segments 1 and 2 broadest; 3 very small, shorter and narrower than any of the following segments, -excepting the distal one; 7 longest. Mouth cone broad, pointed, sur- passing base of prosternum. Prothorax shorter than head, with five pairs of very long bristles. Fore tarsi unarmed. This genus is closely related to Cephalothrips Uzel, but the longer, pointed mouth cone and the structure of the antennz are sufficiently distinctive to warrant the erection of a new genus. Lassothrips muscorum sp. nov. Female.—Length about 1.17 mm. Color blackish brown to black, legs and antennal segments 1 and 2 paler. Eyes moderate in size, coarsely faceted, situated on anterior surface of head. Ocelli lacking. Postocular spines long, blunt, expanded distally. Prothorax three-fourths as long as head; spines slightly expanded at tips ;¥mid-lateral spines and the pair at the posterior angles almost as long as prothorax. Pterothorax about as long as, and slightly narrower than prothorax; mesonotum with one long spine at each posterior angle. Abdomen one and one-third times as wide as prothorax; posterior borders of abdominal segments 2—9 each with two pairs of very long, sub- equal, pointed bristles, some twice the length of the abdominal segments. — Measurements :——Total length about 1.17 mm.; head, length .16 mm., width .17 mm.; prothorax, length .12 mm., width (including coxe) .28 mm.; pterothorax, width .26 mm.; abdomen, width .36 mm.; tube, length .12 mm., width at base .070 mm., at apex .034 mm. Antenne: Mei?) 4a 6 3, 32 0; 4, 42 pp: 5, 42 wp; 6,46 p; 7, 48 p, 8, 36 pw; total, -o1 mm. ; Described from several apterous females, from Arcola, Dubois, Mahomet,” Marion, Muncie, Pulaski, and Urbana, Illinois, taken in moss. 366 Genus TRICHOTHRIPS Uzel, 1895. Trichothrips americanus sp. nov. (Fig. 3). Female.—Forma brachyptera.—Length about 1.7 mm. General color clear brownish yellow with more or less dark hypodermal pigmen- tation; prothorax and basal abdominal segments slightly darkened with brownish black; tube tipped with gray. Head slightly longer than wide; vertex elevated, rugose, sloping ab- ruptly to bases of antenne; cheeks rounded, faintly reticulate, sparsely spinose; postocular bristles slender, pointed. Eyes reduced. Ocelli want- ing. Antenne slightly more than twice as long as head; segments 1 and 2 concolorous with body, shaded laterally with black; 3—8 uniform dark blackish brown, excepting extreme base of 3, which is yellow; 3 sub- conical; 4—7 oblong, pedicellate, subequal in length, but becoming gradu- ally narrower; 8 lanceolate, pedicel- late; segments 3 and 4 each with two outer sense cones and one inner one; 5 and 6 each with one sense cone on either side of apex, the outer one on segment 6 very small. Mouth cone just attaining base of prosternum; labium broadly rounded; labrum pointed, surpassing labium by the length of the maxillary palpus. Prothorax slightly shorter than head, and (including coxe) about twice as wide as long; all spines present, long, pointed. Pterothorax about as long as, and usually some- what narrower than, prothorax. Wings short, attaining base of abdo- Fic. 3 men. Legs about concolorous with Trichothrips americanus, female. a, head coud body, all femora shaded laterally Pane rat. piace ee ora Oe with brown or black; tarsal cups Gary amoprerous foun, G- DB black; fore tarsi. armed will a) argue acute tooth. Abdomen large, heavy, about one and one-third times as wide as prothorax. Tube slightly shorter than head, twice as wide at base as at apex. Measurements:—Total length 1.68 mm.; head, length .21 mm., width .19 mm.; prothorax, length .18 mm., width (including coxe) .38 mm.; pterothorax, width .36mm.; abdomen, width .50 mm.; tube, length .18 mm., width at base .098 mm., at apex .045 mm. Antennz:1, 36 p; 2,90 p; 3, 62 4, 59 uw; 5,62 546, 99 ow 7, 57 38, O7 me totaly opaaeee Forma macroptera.—Similar to forma brachyptera in size; general color darker, the entire body shaded with grayish brown. 367 Head broadly rounded in front. Ocelli present. Eyes large, finely faceted. Pterothorax wider than prothorax. Wings large, reaching base of tube; color light gray-brown, spotted with darker. Male (Forma brachyptera).—-Similar to female, but smaller (length about 1.4 mm.). Prothorax about as long as head. Fore tarsi armed with a slightly larger tooth. Abdomen slender, tapering more gradually to apex. Described from several specimens from Carbondale, Homer, and Urbana, Illinois, taken under bark on rotten stumps. Trichothrips angusticeps sp. nov. (Fig. 4). Female.—Length about 1.4 mm. General color brownish yellow with considerable maroon-colored hypodermal pigmentation; head, pro- thorax, sides of abdomen, and tip of tube slightly darkened with brown- ish black. Similar to 7. americanus sp. nov., differing from it as follows: Head fully 1.4 times as long as wide; cheeks paral- lel; postocular bristles knobbed. Antenne 1.7 times as long as head, nearly concolorous with darker parts of body, excepting segments 1 and 2, and basal half of 3, which are paler. Mouth cone considerably sur- passing base of prosternum; labrum surpassing labium by twice the length of the maxillary palpus. Prothorax about .7 as long as head; all spines pre- > sent, long, knobbed. Legs yellow, all femora shaded slightly with brownish. Abdomen rather slender; tube .6 as long as head. _ ‘Fic. 4 Measurements:— Total length 1.44 mm.; head, Tere. ates length .22 mm., width .16 mm.; prothorax, length brachypterous .16 mm., width (including coxe) .34 mm.; ptero- ae gecicaraee thorax, width .30 mm.; abdomen, width .42 mm.; tube, ae arse! length .14 mm., width at base .081 mm., at apex .038 del.) me Antenne: 1,31 4; 2,49 nw: 3,53 4; 4, 50 p; 5, 53 gw; 6, 50 #; 7, 48 w; 8,50; total, .38 mm. Male—Similar to female, but smaller (length about 1.25 mm.). Prothorax five-sevenths as long as head. Described from eight brachypterous specimens, one of which is a male, taken under bark on rotten stumps, at St. Joseph and Urbana, Illinois, by Mr. C. A. Hart and the writer. 368 Trichothrips longitubus sp. nov. Female —Length about 1.8mm. General color dark blackish brown to black, pterothorax and basal abdominal segments usually paler; tibia, tarsi, and intermediate antennal segments bright lemon-yellow, the tibiz clouded basally. Head about as wide as long; cheeks slightly converging posteriorly; vertex elevated, slightly produced, and bearing the anterior ocellus at its extremity; lateral and dorsal surfaces noticeably transversely striate, sparsely and briefly spinose; postocular bristles blunt, almost half as long as head. Eyes slightly more than one-fourth as long as head, finely faceted. Ocelli anterior; anterior ocellus overhanging. Antenne slightly less than twice as long as head; segments 1 and 2 nearly con- colorous with body, 2 brownish yellow apically; 3-6 uniform bright lemon-yellow; 7 blackish yellow at base, shading to blackish brown at apex; 8 blackish brown; sense cones long, slender; segment 3 with one on outer apical surface; 4-6 each with one on either side of apex, and a small rudimentary one on dorsum. Mouth cone nearly reaching base of prosternum. Prothorax two-thirds as long as head, and (including cox) about two and one-half times as wide as long; all spines present, blunt, except- ing the pair at the posterior angles, which are pointed, and longer than the prothorax. Pterothorax broader than long, slightly wider than prothorax; sides arcuate, slightly converging posteriorly. Wings reach- ing base of tube; fore wings clouded at base, not narrowed at middle, and with the apical fringe on posterior margin double for about eight hairs. Legs slender; femora nearly concolorous with body, the middle and hind pairs paler basally; tibize lemon-yellow, clouded basally; tarsi lemon- yellow, unarmed. Abdomen large, heavy; bristles long. Tube fully as long as head, tapering evenly from base to apex. . Measurements:—Length 1.84 mm.; head, length .25 mm., width .24 mm.; prothorax, length .16 mm., width (including coxe) .40 mm.; pterothorax, width .44 mm.; abdomen, width .46 mm.; tube, length .26 mm., width at base .105 mm., at apex .050 mm. Antennz:. 1) (309. 2, 57 #3 3, 73 43 4, 68 uw; 5,68 fe; 6, 65 pw; 7, 68 4; 8, 46 metoralaeees mm. Male.—Similar to female. Prothorax and fore femora not en- larged; fore tarsi unarmed. Described from ten macropterous specimens (nine females and one male) taken in sweepings at Carbondale, Illinois, by Mr. C. A. Hart. This species is easily distinguished from all other members of its genus by the peculiar antennal coloration and the long tube. 369 Trichothrips buff@ sp. nov. (Fig. 5). Female—Length about 1.9 mm. General color black; antennal segments 1-3, tarsi, and articulations of legs, usually yellowish brown. Head nearly as wide as long, broadly rounded in front; cheeks slight ly converging posteriorly; lateral and dorsal surfaces noticeably trans versely striate, sparsely, briefly, and scarcely visibly spinose; postocula1 bristles blunt, slightly longer than eyes. Eyes almost one-third as long as head. Ocelli anterior; anterior ocellus scarcely overhanging. An- tenne slightly more than twice as long as head, faintly reticulate; seg- ments 4-8 concolorous with body; 1 and 3 usually slightly paler, dark- ened laterally, the latter pale yellow at extreme base; 2 brownish yellow, darkened laterally and basally; sense cones long, slender; segment 3 with one on outer apical surface; 4—6 each with one on either side of apex and 5 and 6 each with a rudimentary additional one on dorsum; 7 with a long, sub-apical one on dorsum. Mouth cone long, attaining base of prosternum. Prothorax about as long as head, and (including coxez) slightly more than twice as wide as long; all spines present, blunt, the pair at the posterior angles longest. Pterothorax rectangular, slightly wider than protho- rax, and about one and one-third times as wide as long. Wings short, attaining base of abdomen. Fore femora not en- larged; fore tarsi unarmed. Abdomen large, heavy, 1.3 times as wide as prothorax, narrowing roundly from segment 6 to base of tube. Tube slightly shorter than head, tapering evenly from base to apex. Measurements:—Total length 1.87 mm.; head, length .21 mm., width .20 mm.; prothorax, length .19 mm., width (including coxe) .42 mm.; pterothorax, width .43 mm.; abdomen, width .54 mm.; tube, length .20 mm., width at base .094 mm., at apex .042 mm. An- Fie. § renne: 1, 30 jue 2, 56 ies 3, 64 {ae 4, 63 [se Trichothrips buffe, eel head and oe, 6, 63 #; 7,62 #; 8, 42 w; total, prothorax. (J. D. H., del.) .44 mm. Male—Similar to female, but smaller (length 1.5 mm.). Prothorax and fore femora not enlarged; fore tarsi unarmed. Described from several brachypterous specimens of both sexes taken under bark on soft maple trees at Decatur, Homer, and Urbana, Ilinois. I name this species for Dr. Pietro Buffa, of the Royal University of Pisa, Italy. 370 PLECTROTHRIPS, gen. nov. (xAjxtpov, spur; Joc, thrips.) Head slightly longer than wide; cheeks full, without spine-bearing warts; vertex elevated, transverse. Eyes moderately large. Ocelli pre- sent, anterior. Antennz inserted beneath vertex, twice as long as head, eight-segmented; segments 3—6 provided each with two or three short, stout, roughened sense cones; segment 8 noticeably longer than segment 7, very slender, compressed, provided with a single terminal bristle. Mouth cone very small, only about one-fourth as long as prothorax, slightly wider than long, broadly rounded at apex; labrum blunt. Pro- thorax large, heavy, one and one-third times as long as head, with a prominent median groove; notum not attaining lateral margins; all spines wanting, excepting the pair at the posterior angles. Pterothorax large, lateral outline convex. Legs short, stout; fore tibiz with a stout, obtuse tooth on inner margin of apex; middle and hind tibize with re- spectively one and two long, very stout, tibial spurs on inner lower mar- gin of apex; anterior femora very large; fore tarsi with a very large, slightly curved, acute tooth. Wings present, not narrowed at middle. Male without scale at base of tube. This genus resembles Trichothrips Uzel in general structure, and should probably follow it in a linear arrangement of the genera. Plectrothrips antennatus sp. nov. Female.—Length about 1.8 mm. General color blackish brown, fading to brownish yellow on abdomen; tube bright brownish orange. Head six-sevenths as wide as long, truncate in front, widest behind eyes, and narrowed posteriorly; lateral and dorsal surfaces very faintly reticulate, sparsely spinose; postocular bristles slender, pointed, their bases situated near the lateral margins of head, and equidistant from posterior margins of eyes and anterior border of prothorax. Eyes finely faceted, moderately large. Ocelli placed well forward; anterior ocellus slightly overhanging; posterior ocelli opposite anterior third of eyes and contiguous to them. Antenne eight-segmented; segments 2-8 sub- equal in length; 8 compressed, fusiform-pedicellate as seen from above, and with a single terminal bristle; 3, 5, and 6 provided each with two short, very stout, roughened sense cones, one on each side of apex; 4 with an additional similar cone on the outer apical surface; circular sense-area on segment 2 situated nearer base than usual; antenne concolorous with. body, excepting segment 3, which is orange at base. Prothorax large, one and one-third times as long as head, and (in- cluding coxe) two-thirds as long as wide; all the usual spines lacking, save a single long pointed one at each posterior angle. Pterothorax slightly broader than long, and a little wider than prothorax; sides rather prominently arcuate. Wings reaching about to base of tube, Safi veinless; fore wings with an apical double fringe of eight hairs, and with the basal scale black. Femora concolorous with head and thorax; tibiz and tarsi yellowish brown. Abdomen large; sides sub-parallel as far as segment 6, thence curving roundly to base of tube. Tube about three-fifths as long as head, ab- ruptly narrowed at apex, and slightly narrowed at middle. Measurements:—Total length 1.8 mm. ({.71—1.89 mm.); head, length .32 mm., width .19 mm.; prothorax, length .27 mm., width (in- cluding coxz) .40 mm.; pterothorax, width .41 mm.; abdomen, width .45 mm.; tube, length .13 mm., width at base .082 mm., at apex .041 ae Antenne: 1, 41 #: 2,52 4:3, 57 ow; 4, 55 4; 5,54 pw; 6, 54 4; 7, 49 pw; 8, 54 mw; total, .42 mm. Male.—Slightly smaller than female (total length about 1.4 mm.). Abdomen more slender, tapering more gradually toward apex. Described from two females and five males, taken by the writer in June on a window of a wood-shed, Urbana, Illinois: This species could not possibly be confused with any other de- scribed one, distinguished as it is by characters of generic significance. NEOTHRIPS gen. nov. (Fig. 6). (vos, new; Joe, thrips.) Head almost one and one-half times as long as wide; cheeks par- allel, sparsely spinose; vertex ele- vated, narrowed anteriorly, not overhanging. Antenne stout, eight- segmented, about one and three- fourths times as long as _ head, inserted beneath vertex; segments 7 and 8 distinct, but united into a heavy, compact club, and with a straight, comb-like, ventral row of either nine or ten bristles; seg- ments 2 and 7 slightly longer than the intermediate ones, which are almost exactly equal in length. Mouth cone long, slender, acute, surpassing base of prosternum; labrum pointed. Prothorax large, trapezoidal, armed with five pairs of bristles. Legs short, stout; fore tarsi armed with an acute tooth which in the male is larger and Neothrips corticis. a, head and prothorax, fe- slightly curved. Male without scale male; b, tip of abdomen, female; c, right t .d 1 view, female; d, right fore leg, at base of tube. Se GD ae dee 5 i Fic. 6 S72, This genus is perhaps more closely related to Allothrips gen. nov. than to any other, standing between it and Plectrothrips gen. nov. Neothrips corticts sp. nov. (Fig. 6). Female.—Length about 1.34 mm. Color nearly uniform light yel- lowish brown, with considerable irregular reddish brown hypodermal pigmentation; tube bright orange-brown, darker at middle. Eyes very small, consisting of a few large, lateral facets; ocelli want- ing. Antenne nearly concolorous with body, segments 1 and 2 often slightly darkened laterally; sense-cones long, slender, segments 3 and 6 each with one and segments 4 and 5 each with two; three bristles on ventral surface of segment 7. Pterothorax about as wide as prothorax, its dorsum two-thirds as long as wide. Wings rudimentary. Tarsi and apices of tibie yellow; femora and basal three-fourths of tibiae nearly concolorous with body, lighter along inner surface. Abdomen large, heavy, about one and one-half times as wide as prothorax; sides sub-parallel as far as segment 6, and then converging abruptly to base of tube. Tube .7 as long as head, and about 1.4 times as long as its basal width; abruptly narrowed at apex and slightly nar- rowed at middle, where it is more heavily chitinized. Measurements:—Total length about 1.34 mm.; head, length .20 mm., width .14 mm.; prothorax, length (excluding non-chitinous por- tions) .15 mm., width (including cox) .29 mm.; pterothorax, width .28 mm.; abdomen, width .42 mm.; tube, length .14 mm., width at base, -095 mm., at apex, .036 mm. Amtennz:. 1,31 "5 2)°54 0/3) Gpeee 44 4; 5,44 uw; 6,45 w; 7, 50 w; 8, 29 w; total, .34 mm. Male.—Slightly smaller than. female (length about 1.2 mm.). Four bristles on ventral surface of segment 7. Abdomen more slender (about one and one-fifth times as wide as prothorax), tapering evenly from segment 7 to base of tube. Described from several specimens of both sexes taken under bark at Urbana and Hillery, Illinois, in winter. ALLOTHRIPS gen. nov. (Fig. 7). (addos, of another kind; Oped, thrips.) Head large, about as wide as long; cheeks full, sparsely spinose- vertex elevated between eyes, and sloping abruptly to insertion of antenne. Antenne stout, seven-segmented, less than 1.6 times as long as head, inserted beneath vertex; segments 3-6 subequal in length, very slightly longer than wide; 2 and 7 longer, the latter with a slightly arcuate row of four bristles on its ventral surface. Sis Mouth cone large, broadly rounded, reaching base of prosternum; la- brum blunt. Prothorax short, about two-thirds as long as head, and armed with six pairs of knob- bed bristles. Legs short, stout; fore tarsi unarmed. This genus is the only one of its family (excepting Kladothrips Froggatt) which has seven-seg- mented antenne. The reduction in the number of antennal seg- ments is a result of the union of the two apical ones, and the whole antenna is an exaggeration of the type indicated by Neothrips gen. nov., in which a separating suture is still distinctly visible. Fic. 7 Allothrips megacephalus Allothrips megacephalus, female, apterous form. = ° a, head and prothorax; 0b, right antenna, Sp. nov. (Fig. igs dorsal view: c,tipofabdomen. (J. D.H., del.) Female —Length about 1.3 mm. Color dark blackish brown, with maroon-colored hypodermal pigmen- tation; tarsi, tube, and antennal segments 1 and 2 slightly lighter. Ab- domen broad, about one and one-half times as wide as prothorax. Forma aptera.—Eyes very small, consisting of a few large lateral facets. Ocelli lacking. Pterothorax about as long as prothorax; meso- notum transverse, sub-rectangular, with six equidistant knobbed bristles along its posterior border, and with an additional similar pair near the posterior angles. Measurements:—Total length 1.31 mm.; head, length .21 mm., width .20 mm.; prothorax, length .14 mm., width (including coxe) .30 mm.; pterothorax, width .30 mm.; abdomen, width .45 mm; tube, length .12 mm., width at base .082 mm., at apex .044 mm. Antenne: 138 6; 2,57 w: 3, 51; 4, 41 pw; 5, 44 w; 6, 44 pw; 7, 67 w; total, .34 mm. Forma brachyptera.—Eyes moderately large, coarsely faceted. Ocelli present; a pair of long knobbed bristles behind the posterior ones. Pterothorax about twice as long as prothorax; mesonotum sub-pentago- nal, with two pairs of knobbed bristles along its posterior border. Wings attaining base of abdomen. Described from several females, one of them brachypterous, taken under bark on various trees at Urbana and Springfield, Illinois, in winter. 374 Genus ACANTHOTHRIPS Uzel, 1895. This genus is represented in Illinois by two species, which may readily be distinguished from each other and from their previously described congeners by means of the following key. I. Inner-surface of fore femora with a single sub-apical tooth. a. Cheeks with prominent spine-bearing warts. No latero-dorsal white stripe. b. Wings of both pairs with a very prominent blackish longi- tudinal vein reaching nearly to tip A. magnafemoralis Hinds.* bb. Wings without conspicuous longitudinal vein A. doanett Moulton, A. nodicornis (Reuter). aa. Cheeks without spine-bearing warts. A latero-dorsal white SERPS cc 4 econ eee arene ba kn VENER Eis Care ae pee A. albivittatus sp. nov. II. Inner surface of fore femora with a ‘‘long, sharp, and slightly curved”’ COOth near DaSekt nek ask en ee ene eee A. sanguineus Bagnall. Acanthothrips albivittatus sp. nov. Female.—Length about 2.1 mm. Dorsal surface roughened with numerous microscopic tubercles; ventral surface smooth. General color (reflected light) dull mahogany brown, with a narrow latero-dorsal white stripe which originates at the posterior margin of the eye and terminates in a small spot at base of segment 8 of abdomen; on the head the stripe is slightly narrower than the basal antennal segment; on the prothorax it broadens posteriorly and includes an irregular reddish spot; at the an- terior mesothoracic margin it is broken up into two subequal triangular areas, from which it continues as a much narrower line to the base of the abdomen; it is lacking on the first abdominal segment, and extends un- interruptedly from the second to the eighth. General color (trans- mitted light) yellowish brown, with maroon-colored hypodermal pig- mentation; legs blackish brown, non-pigmented, shaded laterally with . black; tarsi and inner surface of fore tibie paler; antenne uniform black. Head 1.4 times as long as wide; cheeks converging abruptly to eyes and to base of head; dorsal and lateral surfaces faintly reticulate, scarcely visibly spinose and not roughened by spine-bearing tubercles; postocular bristles long, pointedt. Eyes large, contained in length of head two and two-thirds times, and wider than the interval between them. Ocelli sub-approximate, opposite center of eyes. Antenne about one and one-fourth times as long as head; segments 3-6 urn-shaped; 7 and 8 closely united, the latter conical; sense cones long, slender; segments 3, 5, and 6 each with one on either side of apex; 4 with an additional *T have specimens of this species taken at Muncie and Urbana, Illinois. +These bristles are wanting in A. magnafemoralis Hinds. an} outer one; 7 with a sub-apical dorsal one. Mouth cone pointed, attain- ing base of prosternum. Prothorax two-thirds as long as head, and (including coxe) slightly less than twice as wide as long; all usual spines present, blunt. Ptero- thorax scarcely wider than prothorax; sides sub- -parallel, slightly con- cave. Wings long, without prominent longitudinal vein. Fore femora five-eighths as wide as length of prothorax, and with a sub-apical acute tooth; fore tarsi armed with a stout tooth. Abdomen about as wide as prothorax. Tube about .7 as long as head; bristles at tip shorter than head. Measurements :—Total length 2.1 mm.; head, length .36 mm., width .25 mm.; prothorax, length .24 mm., width (including coxe) .46 mm.; pterothorax, width .46 mm.; abdomen, width .47 mm.; tube, length .25 mm., width at base .092 mm., at apex .059 mm. Antenne: 1, 45 p; Reo sits fe. P12. 5, 100 956,73 vw: 7, 67 > 8, 38 @; total, .62 mm. Described from one female taken on the trunk of a Carolina poplar at Bloomington, Illinois, July 10, by Hugh Glasgow. Genus LiotHrips Uzel, 1895. Liothrips (?) ocellatus sp. nov. Female—Length about 2.2 mm. General color black, excepting tarsi and articulations of legs, which are slightly paler, and antennal seg- ments 3—5, which are at least partly yellow. Head 1.15 times as long as wide, widest just behind eyes, narrowing evenly to base, where it is .84 of the postocular width; vertex elevated between eyes, slightly overreaching insertion of antenne, and bearing the anterior ocellus at its extremity ; lateral and dorsal surfaces transv ersely striate, sparsely, briefly, and scarcely visibly spinose; postocular bristles blunt, three-fifths as long aseyes. Eyes large, one-third as long as head. Ocelli anterior; posterior ocelli opposite anterior third of eyes: anterior ocellus overhanging. Antenne eight-segmented, twice as long as head; segments 1 and 2 concolorous with body, excepting apex of 2, which is paler apically; 3 uniform bright lemon-yellow; 4 yellow, dusky at base and apex; 5 blackish brown, its second and third fifths brownish yellow; segments 6-8 concolorous with body.* Prothorax two-thirds as long as head, and (including cox) 2.4 times as wide as long; all spines present, moderately long, blunt, the two pairs near the posterior angles longest. Pterothorax slightly wider than prothorax, about as long as broad, slightly narrower posteriorly; sides convex, gently arcuate. Wings present, reaching about to base of tube; fore wings brownish at base, not narrowed at middle, with three sub- *I have not described the position of the sense-cones, as several of these are apparently lacking. 376 basal brownish spines on anterior margin, and with the apical fringe on the posterior margin double for fourteen hairs; posterior wings with a weak median vein reaching about to middle. Legs stout, not long; fore tarsi unarmed, ») i: Abdomen large, slightly wider than pterothorax, tapering roundly from segment 6 to base of tube. Tube about .8 as long as head, taper- ing evenly from base to apex. Measurements:—Total length 2.21 mm.; head, length .24 mm., width .21 mm.; prothorax, length .16 mm., width (including coxe) .38 mm.; pterothorax, width .42 mm.; abdomen, width .46 mm.; tube length .20 mm., width at base .092 mm., at apex .042 mm. Antenne 1,36 w; 2, 62 ; 3, 81 pw; 4, 81; 5, 73 p; 6, 67 2; 1, 02 fy 8, eee .50 mm. Described from a single female taken at Hillery, Illinois, in moss, by C. A. Hart and James Zetek. Genus CryptToTHRips Uzel, 1895. Cryptothrips carbonarius sp. nov. (Fig. 8). Male.—tLength about 2.22 mm. (abdominal segments somewhat telescoped). Color uniform coal- black, excepting tarsi and articula- tions of legs, which are dark black- ish brown. Head rectangular, about one and one-half times as long as wide, sides parallel; lateral and dorsal surfaces faintly reticulate, set with a number of short spines and a longer pair at middle of dorsum; vertex transverse; postocular spines long, slender, pointed; spines just behind ocelli about equal in length to the postocular. Eyes moderately large, not protruding, occupying the anterior angles of head. Ocelli moderately large, their diameter about three times that of facets of Fic. 8 eyes; anterior ocellus not overhang- Comair Giana Bee gail mys dng) postericr occlll 70a aa ters of eyes and almost touching their inner margins. Antenne eight-segmented, 1.4 times as long as head, uniform black ingcolor; segments 3-6 sub-clavate; 7 fusiform, Sy i | pedicellate; 8 fusiform. Mouth cone somewhat wider than long, apex broadly rounded; tip of labrum just attaining tip of labium. Prothorax about three-fifths as long as width of head, and (includ- ing coxe) about three times as wide as long; usual spines all present, the two pairs near the posterior angles much the longest; anterior mar- ginals moderately long. Pterothorax about 1.4 times as wide as long, somewhat broader than prothorax; sides nearly straight, slightly converg- ing posteriorly ; anterior corners scarcely projecting beyond the general outline. Wings present.* Legs nearly concolorous with the body; anterior tarsi armed with a stout tooth. Abdomen moderately stout, about as broad as pterothorax, widest at about segment 3, from which it tapers evenly to segment 6, and then rather abruptly to base of tube. Tube four-sevenths as long as head, widest at base, constricted just before apex; intermediate portion parallel-sided, exactly three-fourths the diameter of base; surface not spinose. Measurements :—Total length 2.22 mm.; head, length .46 mm., width .30 mm.; prothorax, length .17 mm., width (including coxe) .49 mm.; pterothorax, width .52 mm.; abdomen, width .62 mm.; tube, length .27 mm., width at base .104 mm., at apex .054 mm. Antenne: pee (ors, 125 4 106 > 5, OF ws 6, 81 p; 7, S57 ps 8, 47 ps; total .65 mm. Described from a single macropterous male, taken at Pulaski, IIL., May 21, 1907, in sweepings from grass and weeds, by Mr. C. A. Hart. Genus IpoLotHrips Haliday, 1852. Idolothrips flavipes sp. nov. (Fig. 9). Female—Length about 3.1 mm. Color of body coal black; all tibiz and tarsi, and at least the basal portion of antennal segments 3 to 6, bright yellow. Head very slightly more than twice as long as wide, narrower just be- hind eyes and at base, widest across eyes; finely striated and set with several stout spines; vertex conical, produced, apex overhanging inser- tion of antenne; anterior portion of head provided with a pair of prom1- nent bristles in addition to the postocular, situated on either side of the prolonged vertex. Eyes large, finely faceted, prominent, bulging. Ocelli small, their diameter about equal to that of facets of eyes; anterior ocellus occupying extreme vertex; posterior ocelli slightly in front of centers of eyes, and slightly removed from their inner margins. An- tennz eight-segmented, slender, about 1.4 times as long as head; seg- *The only specimen which I have of this species has been cleared in potassium hydroxide, and the wings, as a consequence, are unfit for study. 378 ments 3—5 clavate; 6—8 fusiform; segments 1, 2, 7, 8, apical half of 6, and apical fourth of 5, dark blackish brown; remainder of antenna lemon- yellow, excepting apex of 4, which is clouded with brown. Mouth cone about as long as its width at base, broadly rounded; tip of labrum just attaining tip of labium. Prothorax almost as long as width of head, and (including coxe) slightly more than twice as wide as long; surface finely reticulate; usual spines all present, the two pairs near the posterior angles somewhat longer than the others. Ptero- thorax sub-rectangular, about two-thirds as long aswide, and slightly broader than prothorax; anterior corners projecting slightly beyond the lateral margins. Wings represented by small pads, which are about equal in length to the head, and four times as long as broad. All tibize and tarsi bright yellow, the former often clouded with brown at base; re- mainder of legs concolorous with body: anterior tarsi unarmed. Abdomen broad, about one and one half times as wide as pterothorax, widest at segment 4, from which it tapers evenly to tube, giving the abdomen a lanceolate form. Tube almost as long as head, tapering evenly to middle, and then some what more abruptly to apex; surface not spinose. Measurements:—Total length 2.82-3 .34 mm.; head, length .53 mm., width .25 mm.; prothorax, length .21 mm., width (including coxe).46mm.; pterothorax, width .48 mm.; abdomen, width .74 mm.; tube, length .47 mm., width at base .114mm., at apex .052 mm. Ant- enne: 1, 48 mw; 2, 70.4; 3, 140 4:-4,.120 w: 5, 112 pw; 6, 9250 eae S, (0 ws totaly s.72 mana. Male.—Smaller than female (total length 2.58—2.97 mm.). An- terior femora no stouter than in female; fore tibiz provided with a stout tooth. Abdomen slender, tapering evenly from almost the very base. Fic. 9 Idolothrips flavipes, female, head and pro- thorax. (J. D. H., del.) Described from several males and females, all from Illinois, as follows: Dubois, Apr. 28 (C. A! Hart and LL. M. Snaith));) momen Mar. 30, Apr. 17° (C..A. Hart, J} D. BH.) SNsdi” GQ. Bolten eae specimens were taken among fallen oak leaves. — _ a a tn i Gy) bo SYSTEMATIC LIST OF SPECIES. Heterothrips ariseme@ gen. et sp. nov Sericothrips pulchellus sp. nov DADS LOMPIGE DS SPOMOV 25.5) eo. aca nls s vats Suelo ee le cee bes Lissothrips muscorum gen. et sp. nov Trichothrips americanus sp. nov ee PDSTISTICO SESS TOM die AM: Shale vb eee Ben hs SS LORIE SD OW Poe Sit eis Be sie wie ee Ne OUGIIE Si On ANON neces Serre nana RRR ets toe Rn a eae Plectrothrips antennatus gen. et sp. nov Mee SEC OTIGIS SMe eL SPs TOW 4). 5 os. otergen Gs tse WS din edad es Allothrips megacephalus gen. et Sp. NOV...... 2... cece eee eee es PVGaninoInTaps QlOViOlns SP. NOV... 22. 2,0. eee ne eee eae Bie pS )ROCEN INS SPs MOV 352 occ ce ok a ea ee te ewes iaeVLOLNIA PS COTOOVGTIUS SP. MOVs... se a ee tes Mego ies: ADV PCS SO IMON, 6.6 oo es yok ae Ree Kee Ree ee ae ce — OoOOMmONT AO MN FP WN Issued August 22, 1908. 379 BULLETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL: HISTORY URBANA, ILLINOIs, U. S. A. Vot. VIII. FEBRUARY, 1909 ARTICLE III. / ON THE GENERAL AND INTERIOR DISTRIBUTION OF ILLINOIS FISHES BY STEPHEN A. FORBES, Pu.D. ArticLE III.—On the General and Interior Distribution of Illinois Fishes.* By S. A. Forpes. The geography of Illinois is, in its most obvious features, so sim- ple and so monotonous that one naturally expects a similar sim- plicity and monotony in the geographic distribution of its plants and animals. The plan of its hydrography is as little complicated as the geography of its land areas. Surrounded on more than two thirds of its circumference by three large rivers, the Mississippi, the Ohio, and the Wabash, with Lake Michigan covering a narrow strip at its northeast corner and draining a bordering region of scarcely greater area, its other waters flow southwestward into the Mississippi and southward into the Wabash and the Ohio, all mingling finally opposite its southernmost extremity for their journey to the Gulf. Its principal watersheds are inconspicuous ridges or slightly elevated plains, most of them originally more or less marshy, and the headwaters and tributaries of its various stream systems so approach and intermingle that in times of flood they formed an interlacing network, through which it would seem that a wandering fish might have found its way in almost any direction and to almost any place. Its climate varies considerably, of course, within the five and a half degrees of its length from north to south, but by insensible gradations, with no lines of abrupt transition anywhere to set definite boundaries to the range of its aquatic species. Its surface geology is more diversified than its topography, and its soils, although uniformly fertile throughout most of the state, dif- fer notably in their origin and physicalconstitution, some of these dif- ferences being such as to affect more or less the surface waters and, through them, toinfluence the conditions of aquatic life. The extreme northwestern and the extreme southern parts of the state are bare of drift, and their soil is derived immediately from the underlying rock; but the surface of all the remainder of the state, excepting a * This article is a reprint, with minor ‘changes, of a chapter in the introduction to “‘The Fishes of Illinois,’’ by S. A. Forbes and R. E. Richardson. 381 382 smallarea abovethe mouth of the Illinois, has been repeatedly worked over by ice inthe course of the successive divisions of the glacial period. The oldest glaciated area, known as the lower Illinoisan glaciation, covers the greater part of southern Illinois and a narrow belt of the southeast part of the central section of the state. Next to this at the northwest, and immediately east of the lower half of the Illinois River, is the middle Illinoisan; above this, in the west-central part of the state, between the Illinois River and the Rock, is the upper Illinoisan; and still farther north, in the Rock River basin, are the Iowan and Preiowan glaciations, reaching northward across the Wis- consin boundary. East of the last three mentioned, and north of the southern Illinois district, the Wisconsin glaciation, the most recent of the series, covers about a fourth of the state. It is to the peculiar features of the lower Illinoisan glaciation especially that we shall presently be compelled to pay particular attention, because of their evident effect on the distribution of a considerable group of our fishes. The topographical relations of the state to the surrounding terri- tory are as simple and open as its own interior hydrography, and there is little to suggest the possibility of anything in the least pecul- iar in the general constitution or the relations of its fauna, or any- thing problematical or especially interesting in the details of the dis- tribution of its native fishes. We shall find reason to believe, how- ever, that this appearance is misleading, and that the subject, stud- ied in detail, contains matter of unusual interest, and presents prob- lems of considerable difficulty, a solution of which will lead us to some novel results. It is true, however, generally speaking, that the distribution of Illinois fishes reflects, in uniformity and relative monotony, the fea- tures of the topography of the state. A few species occurring in Lake Michiganand characteristic of the Great Lakesare, in fact, the only Ilh- nois fishes which are definitely and permanently separated from their fellows in other Illinois waters by what may be called geographical conditions, and these conditions are not physical obstacles to their passage from Lake Michigan to the Illinois River. Excluding, for the moment, these fishes special to the Great Lakes, we find elsewhere in Illinois a general commingling and over- lapping of the fish population of the surrounding territory, the limits 383 to whose range are climatic, local, and ecological, but topographic only in a secondary sense. THE GENERAL DISTRIBUTION Most of the 150 species of the native fishes of Illinois range far and wide in all directions beyond its narrow boundaries, thus illus- trating the breadth and the simplicity of our geographical affiliations with the surrounding territory; but a considerable number, on the other hand, coming into Illinois from one direction, do not pass be- yond it in another, some part of the boundary of the general area of their distribution passing through our state. Several southern fishes go no farther north than Illinois; some northern fishes go no farther south; some eastern species find here their western limit; and a few western species range no farther east. The comparison of these geo- graphical groups whose areas overlap by their borders here in Illinois is a matter of special interest to the student of distribution, because it is in them that we find indicated the more remote affinities of our fish fauna, and from them, if anywhere, we may glean suggestions of its various origins. It will be convenient for a discussion of this subject to divide the general expanse over which Illinois fishes are distributed, into the following twelve districts: 1, the upper Mississippi Valley, including the Missouri and its tributaries; 2, the lower Mississippi Valley, in- cluding the Ohio and its tributaries; 3, the far North, extending north- ward from the headwaters of the Mississippi, east to the Lake Supe- rior drainage, and west to the Rocky Mountains; 4, the far North- west; separated from the preceding by the Rocky Mountains range; 5, the Great Lake region; 6, the district of Quebec and New England; 7, the Hudson River district; 8, the north Atlantic drainage, from New England to the Chesapeake Bay; 9, the south Atlantic, from the Chesapeake Bay to Florida; 10, the peninsula of Florida; 11, the east Gulf district, bounded by the Mississippi drainage on the west; and 12, the west Gulf district, bounded by the Mississippi drainage on the east, and extending west and south to include the Rio Grande and its tributaries. The following table shows the recorded dis- tribution of our species over the territory so divided. 384 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FISHES | | o ue} | ue} : | : "ep meat | q ie fe) a = 0. | aie Bel lelele| | 2 oo a (21 8le)8\4 a | a |3)3 @ | )-21 al Sis a}a|/ Sls a (a (/4 (Sie la ale |g Sele ls A lel sisi a 5 a G)| 9 ~ |S alaiqis Oo | ga) alee SO Seige! izise SE rath) © iS) S60) 8/Sia| ol] ol Cieeee 6 /Q(D2)ale ja] a |S 1B le |e Silvery lamprey (Ichthyomyzon)...... seaelcteale | ete ads Brook lamprey (Lampeira).......... + AS |) Se Paddile=hisha(Polyodem) tts ses Ace + Ls ae] eon Lake sturgeon (Acipenser)....... + |/+). hae) = te Shovel-nosed sturgeon.............. hope Shall ic le al Sa dn Spine | Ic Wihiteystuneeon (2 Gs DUS) rasa cen. Seal ee eed (see ee eae Wons-nose dy Gar sw tviol urease iene Fee Sees! Wate By lites teint “ote a ae SROnt=MOSeMN GAT tac «,s-cinehe cues eee + Aisne) woes 2 Alligator-gar........ alae esellae |b are. iar | DogtishiCAgi7a) init nce oxsacetetenne rts ap) srl sar se Se |) ae |) Se Mooneye (alosozdes) 3.55 ee ae Bice sees ea eel atesd ede eranth case |oS = eae Toothed herring (tergisus)........... ae Se lle 3) ar) ar Sar Gizzard-shad (Dorosoma)........ + eee | ae ee Skipjack (chrysochloris)............. = ey ee O\elatershae racks. oo Seer ee, eee oe Stee lbaaal “| Makewnerring statins. wtee eyatder ne asin uter oe aes Wake zpro uit Ge ion eee eee anaes + i+). Me ais bax DSL ss SVR y erate ooh ci hres ee Me ae a ae ae lar lee ae ee lee jar ise jar | Black-horse (Cycleptus)............. ee as | a ee fe eh a Red-mouth buffalo (cyprinella)...... Bea aesee ner eats aser Ceeea ol eS «(ha Mongrel buffalo (urus).............. veel alle evel eee rgb ae Small-mouth buffalo (bubalus).......|....\...)... ails ae Sr EN 385 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FISHES—continued Far North ia ie | | oO = | 3 ba | | © gt | ost Ge || sa} a 6 |= l2 q 3 Ps: a |e = gy | o | Sh yee lacs OM IEO| |e Sefer la mM |/4\o/S/S] 8 Hd LS ie Ao TS eee We ieee! of a | ae) Sree 4 Biv igaia o AG |) 22h EEF || te! eos Cos} PISA a om) s ~ » l21SlealelolO] # uw Z iro az) oe, [lea |e lee 2 & - oO o 3 | w = =) Se (es je Onh S| alee el Os) enlace (Oo JOUG |Z lala lA) | P |e |e 8S TENE GZ 20 eee ee bared Pl es is tel I ca 3s =e] Seales | Blunt-nosed carp BEC LCES) a ha ee are Pa Pa ge Se) SF Make carp (thompsont).............- [Pesteae |Metesis aes okie cl ercerlions aed ae |e | | | | | | | | | Maillback carp (veltfer).....2.....56.| + pe el ee ae es (aa be |e] ie || | | PME SICKET. 6 otc ecole es oo es Derep eto taiemlaherlatnalichsnd st Uleeae SEER SSUGKET 6. en io eee ee he | + Hears) Soteictenyficlleraze has looted | Common sucker (commersonii)........ = | + a= a= se |b ipeelese | a5 Hloesucker (nigricans).............- | a5 Pee oor alt sa | ae White-nosed sucker (antsurum)...... ears Vaul F eles oy 4B) a Common red-horse (aureolum)....... + j+ |+ | | se | se Short-headed red-horse (breviceps)..... + | | + |+ Placopharynx duquesnet............-. SA eae ae eo eee eee | + |... Harelipped sucker (Lagochila)....... + | als ae Oe A | ee Sione-roller (Campostoma)...........| + |...|...|...[# |..-;#| # | # [4H Red-bellied dace (Chrosomus)........, + [+ ).)¢ [4 [...f # OF boo) Bevery minnow (H. nuchalis).......|....|...|...|+ |+|.--|+| # | + [+] Hybognathus nubila........... i | + | + ae, Black-head minnow (P. promelas).... moe eee | SIENA Sane eer een Blunt-nosed minnow (P. notatus)....| + |+)|...|+ i sles oar || Se, lar Horned dace (Semotilus)............| + Pe | A sce eal aus | i hea Opsope@odus emilig@........... 0.00 Beoie sy). cl 2 Nea saheie leer Nhat Golden shiner (Abramis)............ fete (ts | es ht teats | relita | Pte. oie 386 TABLE OF THE GENERAL DiIsTRIBUTION OF ILLINOIS FISHES—continued o ue) Me) 2 2 16 12 ae © | Saiee | @ 4 (8) lebote| | 2 eae a |4\5/8/e/8| | @ | 4 /Els rou West els i | a |S|B ~/sleis|Sifini 38) 3 lela a a qi 2 3) = = & % Ge See ea ire) es > e OQ |Z “Ss [eo | o o » Beeb e/8l8/8 | Bi Sis SQ |Z ale la) 2) |B le Bullhead minnow (Cliola vigilax). ... sar iae | ae | ae INCE O DIS ANOLCNUS a le iter enna af a INISIECOMUG G orale iota Sees ci ake i Shida + + | + IN ECOVMEG QU OCAUGGIES fy neha s wiehe a6). erie ete lite INE SHCTOT ODOM wrtle eenereners ons Raven Rare eye ola amet Se Straw-colored minnow (JN. blennius)..| + |+ |. qe) ae [SF |e UN) PPHCHAGODUUS HRI) oioie2 us vs) aos atone ee Oboe alee soe ars INE ROTI D Ors ines Bact teste toon det nusegat ate ieee Rete een | ae Ra ema fsttca |= = ING GHIGGAN OSHS os oho oma 6465608006 a | eae || ar Redtiny CNininensis): swen cecdcrn ccs serots che fesiue | seu et ts ta [eile etl cat pe Spot-tailed minnow (NV. hudsonius)...| + |+|+|+ {+}. a) ar |) SF Silverfin (N. whipplat).... 2. ua. - staal oleae cet ate Common shiner (NS Cormiuius)iw as oc3| ste) ia Note it ate elit Vt INIOLTOPES PISO TATA rsa brea 5, seen a aes fare Aa inal etoliesisl ee ails alae. jl) Sr INS TOOLS so cac0 a6 ane We alee phiner GN. aihertwovdes) e160) chasse alec eae ae || ar INIGLTO PES TUDYIFROUS a=. c4)eedeues ke ee aie aro oleate “elt Blackfin (N. umbratilis atripes)...... =F liste: Wletemelt ae ty Sta fiat EG) iO GNOMGGALG ris arene el Alta ott data Sucker-mouthed minnow (Phenaco- DEUS) eee PRN aleh RRO ASE IEE foe ap ar i Long-nosed dace (R. cataract@)...... ae (Sr loo ar se | ia anal Meg | | Far North 387 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FISHES—continued | | | | oO ms) | ue) E 2 | "st 3 | B: er) 3 | | | Oe Ge ce | okSn eh s ‘a |e | 3 vu | | oy | Sly Ge) a q a lg} | |}m |4\ 5/8 \ S18 Pele iiealae eee ee | ee eel | | ele; |ifeug| eel | (eel eesy gic SS ayes |S eee » 1218lalealol/O| # tw 7, eae l2@ligiPielale| 2@ eo le eas 6 lS ae er hel sag Ne Nicene qu eran NAGS | pes cps een ee | [See Black-nosed dace (R. atronasus).... + +/+ /4+ 5+ + | + Hybopsts hyostomus........000.0000| ey ae eae Spotted shiner (H. dissimilis)..... + + | + Baier chit) (AINDIODS) 600.22. eee eos) bate ei |) th a RORETESECINUD a cicks cecntecie heh sre sates» + Jee} | | sar River chub (kentuckiensis)......... + lets I+ le SSE sete fe Se Flat-headed chub (Platygobio)......4....|.. Je. -|ee. eee [ee- cf fe [ele | | | | RAIS GAG (JAICOIUS os ce ee ee eels we fsele a ee sec eel ee se sag alae lise | MP ORAM UILLG ce alas ess tt aon ee foie ea (a's cea eles e[e ers laws leafs lcteiles Channel-cat (punctatus).............| + +i+) + | + |+)...)+ Great Lake catfish (/acustris)...... | af \ae ema | Yellow bullhead (natalis)............| + Vee se |e le Common bullhead (nebulosus)........ |} + |+/+ | ape + Foo Moelle | sla5 Black bullhead (melas)..............) + natal miu iced ea | | eM, DLN mie tag a) pele Sy 22 eres (elas c|eoa[oeetes olen cles ote | ee, 1 a alain Common stonecat (N. flavus)........| +. |...]-..|+ oA Selseklaaaal| St |. iadpole Cat (S. SVTINUs)........2 65> . t+. ae ae ae | ar Freckled stonecat (S. moctwrnis).. 6. -J..sdee fools fee ede fee | =f eerste ae Slender stonecat (S. exilis)........ af ae . | ar |) ar | | | | Brindled stonecat (S. mturus)....... eats A eal salae cll ce | Sr | ae he Pam RE Mee a) rt nn sos ceed f) ES | AE) ace | eaten es «|e a | Pe Grass pike (Esox vermiculatus)........ + | ets place, ict ce Its 388 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FISHES—continued Piles (ERUAVGews) mrnaisn niterses eee ae: oe Maskall wage cass ih etiam elena Menona top-minnow (F .diaphanus m.) Striped top-minnow (Ff. dispar)...... Common top-minnow (Ff. notatus).... Chologasier Papillay ers a) ce cr ayes et elon pas eal cect eet erate |sse a aeteal eat Viviparous top-minnow (affinis)...... rece alts tla Broolkisticislebacks ee ey aniline) toes Nine-spined stickleback............. ETOULSPEECI Negeri ute cullen tnaneuieewats Birookisilversideharce rin ine een Pirate=perclie Ti Metin maitre eters Pigmy sunfish (Elassoma)........... Beet Seetclle Ua eee White crappie (annularis)........... Blackicrappien(Sparo7des).. sere ace IRoVeraGl UUM Ne. cA nas douasoeace sone etry |e pee se FROCK AG ASS iiss aplenty Ho seen pores te Warmouth (Chenobryttus).. Green sunfish (cyanellus).......:.... NEC DOILISHES GHA TINS aaa eee eee ees A ees farte al eee nee esl lec alels L. symmetricus TE SCURRY O MUS: Meaceate ets wt aaah oor er sc) 3g iol) ie) S "2 lena ae Oe ike q @ Wiel lela) een am |2i/eleie/e| | ® | 8 1alg 2 eis ls(s\5l4| 2 | 2 lalale we}, |ze} || (ou SE) |] RS! 4 Seale |e /e/2) = | = [aisle 2 | Sialsi|s/s |e ele ea ~ » ESSE /E/E/S/8| 8 | B iS lal 6 jQHi4lalela|4a)P |e le le + | + anal ab) Bae lose) se + +) + + Jf + + + J+) +] + [+]. +)+[+}/+i + | + |+}: ak + +4), ee i+ + + +. | obit + |+)...|+ (+) + + + J+ ft iti +t | + + Jt i+ l+ i+) +4 | + | +|...f+ | + | Ur Weel ee | | + /+]...J+)4+]f4+]+) + | 4 bes ol taal | tl tl ena | | | + lt f+ f4]4+]..J+) 4 | + Jef. f+ + J+ f+ lt) + | + +i. + | + | + +i, a Aaa PAN Gabe ae 389 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FISHES—continued o | | | | Bolg |S aa elke q @ J ‘a |B | = 3g | 3 | x » |.2}.0 | 2 & GE oigir M |/4|o|/S/8] 8 eh ol sclg eae |e lb | 2 |e lle Vret || Sex (ave =| Ags ae Sisleisistelel= le cals wey o|] oO} aia ro} So H H | Z, So a PIS TElY 2 Q se o | % 3 n| £ Ser A | ce H 3) 2 ° O | @ e) a iS ia} OJ Z\a le ial} P |e le PRABOMIS MINTALUS 2.6 ee ee slo ees led cle altect a's Vite aricity anew Monug-eared sunfish................. = Jt pe i+] + | + f+ | Orange-spotted sunfish (humulis)..... pie ee ee ess Ree eee ect al fete eae PECL (PONIGUS) ince. oe oe ces bee Wee Siam ae |ar it ae kare ise) apomotis heros...........+++ ales alicranle Pumpkinseed (gibbosus)............. se aRiare ae ar lo +) +] Small-mouthed black bass............ + Jt + /4 040...) 4) 4 4) Premenoutined black bass....-.....-| F pe (Fie i+ lie | ope le]: Paike-perch (S.\witrewm).......5..+-- Stee Wate ve lites 'stp | eicealichee |e oes shots Sauger (S. canadense griseum)....... qe ae | + PEM CHC Os fhe swith ibe eee 2) S54 Seles Steam iets Moc-peren (P: caprodés).............| + |-e|...|+ |. giae | ae lar |lsr | Hadropterus evermanni.........0..0.\oeeslee slew fos sleesfee eles. ap |i ar BEIIRONOCEPUOIUS «005.0 0002 sae en ese s| oF ae, jl Mor Black-sided darter (H. aspro)........) + Atami S| ae 45 Hadropterus ouachite............... Se 0 EDS a | + | ae ae 0. OS ee Oe cdl endl Ockcl eae dened Seka eseeo} lai a|a2 |e Cottogaster shumardi................ a ae ae eects | | Green-sided darter (blennioides)...... + 5 el eel Jeelb] + | + Johnny darter (B. nigrum).......... ge [eee | Sey ae) Se ae Boleosoma camurum........000 cece Cares ite oe ae iar | se lap ie | Far North Ft t+ t+ $f 390 TABLE OF THE GENERAL DISTRIBUTION OF ILLINOIS FIsHES—concluded o : : @ Se oy ae q ‘cd fo) a © ames q ® 415 lolole) | 3 eee » a |4(\8ie\s)e a |e |2)% Biro | | Soles gj | gw |S) B mg | RA se |e | tl ee ee Ey Ten ate a rete 5 o Z S SyslElS/5/a| £1 &18ls 6 |G)miz\alela)a | o |Ela Grystatlaria GSPrella, cute Sia ike pies + + Sand darter (Ammocrypia).......... + + | + |i. Banded darter (E. gonale)...........| + tt] +t f+ Blue-breasted darter (FE. camurum)...| + ;+ | + ESF COSIOMG LOWE toe a nieces ete a oe SAY ea hore ned eres is ci te FP OSSUO etree CR uta EN cern ae es eee + «| te) ste aha hata Rainbow darter (EZ. c@ruleum)....... ta sla «|. op PS aera Etheostoma obeyense.............5+- Pa el Hoss ee dierent a fiat oa Poe SSQUAWIGE PS ere Aue otras wleuss rotate Le) Olea a) alee aie Fan-tailed darter (E. flabellare) ...... ap se be o|ae Poe ole ase. I) ae Boleichthys fustformis............+-. Set ate eevee | te lea ote ce Least darter (Mzcroperca).......2..: SF UlarelE alltel aes White bass (Roccus chrysops)........| + |+ | Wises | ste Wellow bass (Worone) tesa c.e se ae ee col 2iralig setae ee se |) ar Sheepshead (A plodinotus)........... =e ar | Sicha os). cic | WGRIESS WombbeN Dg doo 0 suacdano ose naar ateiamleicitartibace lasik a) TF OTS FIGCU AM rs uaee i lene ayer denen or Uranidea kumltentt............-+-+:| + Bitinbote Clog \aeraes vier bee pene nore tei se SP ar je ae | ar [sees || —— | ————— INumbernorspeciess een ere ein 108) 53} 19] 40] 45) 23) 56) 134] 131) 47) 4 | Far North 37 391 Arranged according to the number of Illinois species in each, these districts succeed each other in the following order. | Per cent. of ee tee | No. of Districts | species | all Illinois | species Lower Mississippi and Ohio valleys.................| 134 89 Upper Mississippi and Missouri valleys............... sigs 87 TES (Saree 12 oF So i ee | 108 | Me: RE eee CISCII@ bes eo Ae eis oe wet Sis we elpue asi ove 56 37 Quebec and New England.. S Ncrters ay Ae ree 53 36 The west Gulf and Rio Grande district.............. 47 Sil PERSO EMMA GIENTIDICTOUSHEIC hes occ\e isis erect G)teco Be ee nb eek 45 30 PeEetOLEMTAGIANGIG {CISC scp: ie al2|elgl elalalz)al iis 5) 3/2/84) 9/4] 2/Si2/ 2) 2) 413 56/4/83 /3/S/4)e lea) Sl2/ 8) 8 i052 4} + | + | }1 f+ ]+ | + Zs ne ieee | | ee ar jij 3|4}4)./2) 2 |e Ae lealice | Oe ee 8 \aubee 7 ee ee ie ball tes baal benz, 3. | eee Zl ete| a3 2 +) +]}+]+ a wiped (a) ol) +]. | + (20a + |. | +] 0 | 0 + [+] + | + +) + ]+ f+ 1 2 |. :| 0: eRe 18 vesta los 9 |. 2 1 | See 1 Ee a lean qe | se 1 AO ellie 9) 2 +) + ])+ )4+ Bec yates hed 2)-4) 4.17] 44 Se 1) 6) 544/..) 8) 15 1 24 1.13 |, 3 eee HOM aA eid sees +} + | 0 1| 19 | 39 V1). 8 loa | 395 INTERIOR DISTRIBUTION OF ILLINOIS FisHES By RIVER SYSTEMS _ SPECIES AND NUMBER OF COLLECTIONS OF EACH—continued Districts Sections | BY | Saeed eae | 80 5 | es Gms: ge gsm (IR =| % 2c aa ee el i E Beals beh atl cg ie 2 eh oe (eee ae Ba ia i Pe er | Be) sisi ala) aisia|2| el 4/2 3 | Soles] oon eralivcra mace e) ISo|e/S|s|/S)/M/E lala) S| 24/3/32 (al a ces ca Chub-sucker.......... 2) 45) a8 2) 20 147 619 | 40 |e |p eee cuemeeeeseker.....5...| 4 | 1 | 13 | 1 13} 16.1) 4 Se) ee Common sucker........ 1 | 14 | 69 9 AS ed ah ly | + 1+ + Long-nosed sucker..... OU de leer baal | 1 Oe | Mepesueker..........-. Th | a oust 1 OR ea 1+ | +- |+- White-nosed sucker..... ...| 2) 14 ]+ 1 \ ae) ae || ae | | | Common red-horse..... Dales 1390) | Se LON E25 sa 2 Vecteaglt ore ae Short-headed red-horse.!.. : 4] 39/1 3 7 2 se | ar i ar || ar | Placopharynx duquesnei|...| 1 1 = 1 ue | Bre) acai eae Harelipped sucker...... Ths lkeovoserad ae aR sll! {Oe |) OP |p ae Stone-roller......... esl 20 || 99 14 roo 365 (ie | We | Ot ee ae ae Red-bellied dace....... 4 | 13 2 4 | ar | ae [ar Silvery minnow........| 2 Gaipsow el VO 104) 27) Oper So ea eet Hybognathus nubila..... 1 3 1 Hae fh ce al) ae Black-head minnow.... 8 | 67 12 6 5 j++ | F | + Blunt-nosed minnow....| 3 | 33 |162 |3 | 19 | 31 | 77 |8 |13| 25 || + | + | + Horned dace........... Pe COU £2 16} 10 |) 24 |4 | 6.) 44) + | ey + Opsope@odusemilig..... 3 AOR! 1 1) 1 USS Ol Aa eat 396 INTERIOR DISTRIBUTION OF ILLINOIS FISHES BY RIVER SYSTEMS SPECIES AND NUMBER OF COLLECTIONS OF EACH—continued Districts Sections RY | aa Sedies Ele a eS eee | al eee O28 ates | Sealed ee 2 a)/%}/4/%| #) 4) e/3),/ 4) < S)a4/S/S/S|/e/Flalal 3/2) 8le Golden shiner.......... 1 | 18 lisa | 1 19 | 50 |7 10} 10 | + | + | + Bullhead minnow...... 1 | 14 [110 522 | 38 |4 | 3) 2) |e aemeaes Notropis anogenus......|...|....| 2 + | 0m eG Notropis cayuga........ | 1 4] 29 |2 5 1 1 “Ee eke Uae N. heterodon........ Sst t 4 3 + )+)+ Straw-colored minnow..)1 | 22 /108 |4 | 9/| 6 | 44 ‘leat | Si sei) Ar Notropis phenacobius....|...|. 2 | “| Onsiag IN BY HAG ain Mat sie Sad ere Boel tech d pails 10 2 “elected N. illecebrosus......... eee ee 1 ily) | + | +/+ )+ Spot-tailed minnow... A ESSA Aae ne 2 | ap sr |) se Redfin. i... 4. 0:..00s:h0c| 4142 |9 [46 | 4), ...]4 9) g0" geen Silverchair e ee 3 | 34 [116 |1| 8 |.29| 7112/3) 6 aie Common shiner........|1 | 19 |105 Mil) 1s |} Be 1/12) + | + |] + Notropis pilsbryt....... oe 1 + 90) alee Ne gejuiusse ee | eS 2d aol to 5 2|.5 | | eee Shineras. ev usierte dene 35) 8ile82 16.) 28 eA On| aelouladd | + [+] + Notropis rubrifrons..... 2 ee Sune | Semele || 8) Bilackhnr se 8 eae cease 2 9 | 67 3 AS SO |S: [ial fp ate | ap. Pap if ae Ericymba buccata....... 4 2558 di ar ii @ ose | se INTERIOR DISTRIBUTION OF SPECIES AND NUMBER OF 397 I_tutinois Fishes By River Systems COLLECTIONS OF EACH—continued Sucker-mouthed minnow Long-nosed dace........|... Black-nosed-dace...... Hybopsis hyostomus.... . oie Bemctea Shiner. .........|..-- See TEC MTD! < coh os cle ceca l's one's Beorers chiub:......... oe 2Uiniare (lath ae MITER GAUGE) ole eck ec: cove = ese Peele st ns Ictalurus anguilla...... Bee erammel-cat.... css. oe bad Common bullhead... Black bullhead ... Mud-cat......... 5 OGG A SE gee Districts | Sections 2 o| o ars a3) eles) | 3 alee A = ~ al pe eb ee ler a le SMe oiled teeta) Ree ot Seales cll esl oh gayle og 2/8) e/S| 8) 4] 3 lw) 2) &] a] 3 Sra pals )S (S|) eine) o |e | ole NAS | 78 Ve asta tom fe ane g | + steer isl 0.) sOulpee pleas | (lanai Deo sp eMedia fl <3 it ae: ee 2 LO e372 |e Aeon ee ol ae ae 7 5 Aas | ey eee 1 | 12 | 90 8 | 10 | 16 feces ie hae Flat-headed chub...... ee asec es ecto istettolicceecoleetelerealt Geom LO, Oo };+ 1 1 | oe Onan + + So et 17 |108 Talon zero | ti 2) + + | + ee A Eo Perorae bas aS 22 10} 18/3 }4| 6] + |+]+ 42 i pet Fag ere eee ee ee daitaa ie | 40°) 45 \ 354 Vel 40 fee ati Seah S| Pale tall ot alee feeraia tae |e Gt oteestieea. Wa 49 +/+ ]+]0 2/132 |...) 11 | 14] 21/3] 8 gl aioh ae Nee 398 INTERIOR DISTRIBUTION OF ILLINOIS FISHES BY RIVER SYSTEMS SPECIES AND NUMBER OF COLLECTIONS OF EACH—continued Districts | Sections | & | »| © | rune | e| | slel e 2 | a Buie epee Do B | ey iter ee lel ee fe a aa ms | Re lgeteas Real bac ee ta | = 5) a) 8B) S| Se) Blala) és] 2) 5) 3 Freckled stonecat...... Pat lara har 1 =e | OS Siets Slender stonecat......./ 1 1 2 2/+ /+]+ Brindled stonecat...... sicbalemeasil i al 1 | 26 3) LO ete eee Mud-muintiowats24.505. Bees ol beach al 1 AA Sieg ames F Grass; pike vere ceasae eas Se ees eile taal A LA AOS OG sO | Bee lice olin Bile: Heke aoe coer ell eon eatieel te eee 1/-+|+1]0 Miuiskaililtim essere eeielaeieta esta es | Oy @ Menona top-minnow....|...|....} 11 | 7 =F | Be | mig ah! Striped top-minnow....|...) 1 | 75 | 1 8 See | a eae Common top-minnow...|1 | 6 | 66 6 | 23ele SS. Sea ieraoe | + +/+ Viviparous top-minnow.|.../....| 1 1 2 PS) | Oe hes) Chologaster papilliferus.|...|.. 6 | Oo) SOR ears Brook stickleback...... pel eeaie tlehi2 | +2 | SOS Nine-spinedstickleback|o..|/)55 <|.5- | | mie (eri oL) WrOut-perch’..een ee am: Boel esreP pac (il Srl | ae iar’ | © Brook silverside........| 1 6 | 89 | 2 2 e204 Sire oF Pirate-perch.: 42.02.40. LAs A Sa (22) 9 | 18419 111) 26) Pigmyisumfishi.. 2.4. eee leseerie clare (a doe et eesetallet- ae 5 1] 0 Oe a 399 INTERIOR DISTRIBUTION OF ILLINOIS FISHES BY RIVER SYSTEMS SPECIES AND NUMBER OF COLLECTIONS OF EACH—continued Districts Sections | ie | | } al | } | een | | | cee een | a & aw | | |. | een pc Rae } | 2 H | | 5) HI @ oO Gee Wace hel lecrn |) ca | Bail” |e | le lee al eel le} | 3 HS Se etl = a iat = ie? a Go a 13 | | | B | 3 2 RENT QA eel | s| 4) 8 le) a] 4/2 lee) 8] 2) 2/3 eS 5 SEI Wee ae a (BOD) eta aces 5 | lore |Ale|S|/M/Elmlal dial oja | | Fal Wibite:crappie.:9...... Be Oe EL Op 2s | 13 WE SS) ON Se) ae. |) se Black crappie.......... Pee See sOnls (tS So | 43) ise |) ael +/+ + ie, | | | aad sunfish. ...2..22|...)..-| 1 or A ee) SOs, Ome rel Sepeeeer es | ASS A) Sb 2) a lade.) 2 ee le | Se Warmouth............|... 3 | 83 3) 5|10/6|6/11))+ | + | + Green sunfish.......... 2| 20 [158 |...] 16) 33 | 57] 7 12] 15} + | + | + Lepomis ischyrus.......... 1 | 3 2 eee se ae eae |) (0) | | | | MMNIEEIAETNS ofa asareie, <=. %)\-9 d's. lan-|.-+-| 24 |---| 1 | [lee elt eapes Nae esel Sreell oe ae Long-eared sunfish........ WMeselazclrtc|: 27ST Ne | 8 Gee eee ieee hao | Seeenee potted suntish..|..-) 5i/192 22} 22.) 25 23 2) 3'| 3) | | Red seb. ss. ba ee 794 | 6 3/38 }1| 1] 6 We. eae Eupomotis heros... ..... Sabet 5 LAE Ora On! bats Pumpkinseed..........|...| 4] 82/4] 2 | 1 Ta eee eee ts | | | Small-mouthed black 225. ee 69 |... 5 2 8 | 1 Sillege |i ae. | se oat | Large-mouthed black | | eee ee eae eos 4b tou!) Soles oal 2A ety lf. ar Rate est | | HE) Ee re ee Re 2 ae a a VP sd i alee en lca ec 400 INTERIOR DISTRIBUTION OF ILLINOIS FISHES By RIVER SYSTEMS SPECIES AND NUMBER OF COLLECTIONS OF EACH—concluded Districts wn 4 o| @| S a) i sz] § Dall coal ee lal eae Bat | | Ay Goal ees el ere a ela = Ee awh ome oi Stailliare oe Wee tee eee ioe Ole Palais | Me DAUGS ees grist te seek alae Le eS 3 1 Wellowsperchine see all lMetea faded 6 Wopeperchy cua ee se Aas tes 5 9 8 Hadropterus evermannt..|...|....| 3 Hf. phoxocephalus.......|...| 12 | 58 SLs a, Owl: Black-sided darter...... BN iS || WO i P22 |) 4 Hadropterus ouachit@....|...|.... 1 Ue ADO SE ated eo peste anton Sore elke tl EVER SCCCMUS © Sata oy ikea Bis een aes eel 1 Cottogaster shumardi....|...|....| 14 |. 2 1 Green-sided darter...... Bana 8 aia ear 36 Johnny, Ganter..a-e. are sy | 2 Milo sil) lO) | 27) ie 5 Boleosoma camurum....|...| 1 | 45 | 2 2 melee aele7) Crystallaria asprella..... leet 2 1 Seba GEWANSIC, Coo oo dso 6 pe tare 7 1 Za Bandedidarterma-ee ce cr olnie tone ae 1 Blue-breasted darter....|...| 2 GR lis eotecesllkete ae Etheostoma tow@....... Sao ers 7A ela hebeer cite’ Nees? PE SSA uN arlene Seal 4 119 | ab |] aa | Big Muddy Saline 11 Sections S S§i2|3} 28 | + | + | 0 | oleae 2+ )+4 1+ | o | + | 0 |e ae eee 11] + |e | o | oO |+ 1+ lolo Io + | 0 | o |} 1 || 0 + | + 8 | elie 10) |) ee ;+ | +] + [+ +] + Pee ere | =: 1//o}|+ ]0 1 | ones 4) 42 | senha a a re 401 INTERIOR DISTRIBUTION OF ILLINOIS FISHES By RIVER SYSTEMS SPECIES AND NUMBER OF COLLECTIONS OF EACH—concluded “T — — ae — Districts | Sections n | = i Oo 2 | SYR) | o Bl oy cs (= oF $ 5 5 A ba > 2 PIAS GSS Ps a | 8 ie) a (S) “ [a4 < Q, ay, ro} 2 | a ~ n = a7 n irr = A = a “a | 00) x 3 |S | oe es S| ie S\alelso\u) elie! silel eis i 3 (e) pc} 4 4 is°] aieet Lx) Fel O} O|4/S|2|/S)M)/ EF lala) dS] 24] S| a Rainbow darter........|2 | 9 | 39 1 DOM de | Aegis la. eet Etheostoma obeyense..... AS cll Ger ata loecacecl cal rene =e Saas ice eval Ary| OF) @ || Sr He. squamiceps......\.... Sos ee aoa ee eRe eee 1 SF Ses foe al ot ane OS ay | Fan-tailed darter...... 1 (Oyj? alih Hae al eal 4! Sallaire tere || st isalechinys fustformis...|...| 1 |. 13 |...|....- §5|18/3/}8] 8] + |+ | + east Garter: . 2.2.22 eel alee MOI ler Alst. poe, eee mela ote Oo; + | eeretass 2.5.1.5. -| 1 1 2 | 36 12°) 12° |e cal saleewles of QWs oe le Yellow bass...)....... LMC SESSA eet a ama (ee a Ned ede aa Pare ey ne Sheepshead. .......... Moimetesasoey tetas 01 ei |i Mall eich sale Mehers thumb ........ Breteler alc DA yl oe elev fe, Beh altar laces Boe ona es eels ‘CDETIS (FIRGIS GE OIL TE ee | a eee etter aS allt ecoal| th che ail eee, + (0) (0) | Uranidea kumlienti....|.. |....|.... Pee eects cal ete alte Stee ee If te) || S707) OY6) i cia ee ae io) elk gee Pees dee Ml Dt |} + | + 0) THE ILLINOIS BASIN AND THE OTHER DISTRICTS COMPARED The key to the distribution of Illinois fishes within the state is the species list of the Illinois basin. Covering fully one half the area of Illi- nois, and extending in a broad belt diagonally northeast and south- west across its northern two thirds, this basin contains nearly every variety of stream, lake, pond, and marsh to be found between the 402 Great Lakes on the one hand and the giant flood of the Mississippi on the other, and it is to be expected that its fish population will be highly typical of Illinois as a whole. It includes, in fact, more than four fifths of the species on our Illinois list, and the special features of the various other basins and areas may best be seen by comparing them with this characteristic central basin as a type. The following is a list of the species of the Illinois system obtained by us in collections, arranged in the order of the frequency of their appearance in 1,115 collections made from that stream and its tribu- tary waters. SPECIES OF THE ILLINOIS BASIN, AND NUMBER OF COLLECTIONS CONTAINING EACH Species Collections | Species Collections* | | Goldentshinen eee ei: 183 | Common red-horse....... 90 Bile cil leery caer eee tase 179 Gizzard-shad............ 89 Blunt-nosed minnow...... 162 Brook silverside.......... 89 Greeny SuniiSh sees ance e 158 Silvery mlinnow.....5> me 86 Black) bullhheadats sone. 144 Warmouth. 2.5.2 saa ae" 83 Redfin (lutrensts).......... 142 Shiner tees hes oe ee 82 Large-mouthed black bass 135 Yellow bullhead......... 82 Spot-tailed minnow....... 133 Pumplinseed..-.2 555: 82 Tad polevcatinescs sate cea 132 Notroptis heterodon........ 81 Blackicrappies seas. eee 130 Sucker-mouthed minnow 78 Etheostoma jessi@......... 119 Mellow perch. 2.) arein an: 75 Wihttercrappies. es: nen cre 119 Striped top-minnow...... 75 SPhVenii. Cee ad a ease ae ees 116 Morned idacese a. ree 72 Orange-spotted sunfish... . 12 Black-sided darter....... 70 Bullhead minnow......... 110 Common /suckersio3..4 69 Straw-colored minnow..... 108 Small-mouthed black bass 69 *A cross (+) in this column indicates the known occurrence of a species which is not represented in our collections from the I]linois basin. 403 SPECIES OF THE ILLINOIS BASIN, AND NUMBER OF COLLECTIONS CONTAINING EACH—continued Collections | Species Species Collections Mhannel-cat. 0.2... ese. | 108 Wa clefimittt pace pre ere 67 Common Shiner... 5.....- 105 | Black-head minnow...... 67 Nounny darter...... 22). 4%:.1 100 | Common top-minnow .... 66 Eee -FONMET .).. 0... 25 8 | eo | FIO SSUGKEIe weariness Cee 61 MesllowrOAaSS;.\. c\.a os eek | 95 | Grassipikes scm om ae 61 BETIG EDS ce ccs ciclsd 2 eos 90 | Hadropterus phoxocephalus| 58 Blunt-nosed carp......... 54 ECE facet ccr as Be: 17, PEACE -PCLCM cic as vj ns 6 54 | Notropts gilbertt.......... iis Sheepshead.............. 53 | White-nosed sucker...... 14 MAOrENOSed Saris. i122 2 - 52 | EDOM SPOTClii/nescvereversreqe r= ait 14 Opsopeodus emili@........ 49 | Cottogaster shumardi...... 14 BIO -SUCKET . oasis ees es = 48 Striped sdeker..n).. 4 13 Small-mouth buffalo ...... 46 | Red-bellied dace......... 13 Boleosoma camurum....... 45 SENEIRSEo Gd 05 or 13 Common bullhead......... 42 Boleichthys fusiformis..... 13 Brallback Carp ..i.c..5. 5. 39 | silvery lamprey.......... 12 AI DOW Garter... . 0626. 39 | Menona top-minnow.... . 11 Short-headed red-horse. . 39 | Pan-tailed darter... 324°. 11 Long-eared sunfish........ oi | River CAEP ctoti caine os ctnneters 11 RMEMIECUBASS < . 3.00. 5 so 22 2s 36 | Least darter... 10 BROCE ASS 50 oes ee me 35 Vee icoarer aetna ar 10 BPE BETCH o66'oc) oc o's 9 a sls 35 ll) Paddle-fich <7 Species oe n ea (ec aah te a He, ca Fa era NS ase Se he eal 2 9 3 rd 2) 3) 5 q 3) & ° 2) a | Gages aie ce) o a ) se) at a) & rl Qy fa) fo) aq a Wa) q S| Ce ae elec adam ie seems pe) Ke E EP ele al il2i 2a ee Ach ft) g/a/o0/)8)|14)a!la)| > ae 289 | Common sucker......|132 3 | 19 | 71 1 | 49° | 39 | 47 1) TAO Sis ZOAN ALOSSUCKER yey. vie lete: 99 | A W631 25 i 4 7 20) 563i 54 302a| Chub-sucker..........\131 Ol | Sy 4s lB Se Wp aks 57 | 32iaiese 303: 1) Striped sucker... 2.55.40 1 2) tay S850 03 19 | 26 | 32 305 | White-nosed sucker. ..| 18 i | 24 ) BO Oo Wes cclicese ills ae alle cere ell eee 314 | Common red-horse... .|143 9 | 32 | 40 4 | 47 | 57 | 28 | 15 || 65 6 | 55 319 | Short-headed red-horse| 55 | 13 |.25 | 15 | 22 j....J....]..../.... 14 | 14 |) 4 328 | Stone-roller.......... 195 ny Ae oS) 1 | 65 | 63 | 23 | 14 1105 7 VS 334 | Red-bellied dace...... QBN LO: feoscscah FAL IRS 20a Pee ee ee | 340 | Silvery minnow.......|183 | 12 | 36 | 32 7 | 30 | 47 | 40 | 13] 67 | 33 (54g 349 | Black-head minnow...| 95 | 14 | 30 | 48 AW GD || SO) |) 8 || 440 12 5.3 350 | Blunt-nosed minnow. .|376 5 | 34 | 43 | 12 |108 | 50 | 34 | 16 202 | 20 | 46 355 | Horned dace......... 151 4 | 28 | 63 2 || 42 | 48.) 36 | 116°) S19 17a 391 | Opsope@odus emilig....| 40 | 13 | 6 | 36 | 32 .eeele ss nn 394 | Golden shiner........ 303 | 12 | 17 | 29 | 32 | 28 | 32 | 57 | 11 | 820) 445 ecm 398 | Bullhead minnow..... 187 | 17 | 31 | 28 7 | 36 | 67 | 17 | 16 || 62 | 11 \o4aeee 405 | Notropis cayuga...... 29 }....| 13 | 26] 57 | 13 |.54 | 38.) 8 |e 406 | N. heterodon..........| 92 | 19 i ipa fs Sa ea GX O Yn enamel eres ie tate ec 14 7 22 408 | Straw-colored minnow |185 TN AAS eSy7 3 | 63 | 49°] 26 | 25 [103 | 10 | 50m 429 ECOLOGICAL TABL E—continued ALL ILLINOIS SPECIES WITH AT LEAST TEN AVAILABLE RECORDS EACH | g i Water (97 species) |Current (49 species) /Bottom (62 species) Z, = cA. | wn | n » n g g a q Fs 8 ls el) eae os § 5 [ol] S| | & 5 5 Species = D ee eo Nat eS Kis . Oi 21 o St MOM large 2 a) a | & cof eo o > € 9 a (e) 9 a 8 - Di) se) Ae! fe) o oe | @ Le) 8 fan |) Sc eee (ecole cet) Obes aq | 3 § Re | A ue Wi St | ee cee rl) a8 Sag a/ mlal ses) 213) 8)] 8) €] sia] si] E 2 3 g ie ey > e | 3 a > 3 } S 2 SCs ervey Ou ml q 2) g fe) ro) q 2) 278 S| 2 Sele ie) — q a * 5 Al fa | oe | ae) ees 3 Sela lost om I oa eee |) 22s! il = ue) ee See Si Syl) 2 G. |) =a) Cl eee 3s | 0 a > 6 | & we oe > BV esial aaee = |S =I SON 16 30 P44 2 Sea ee 1381] White crappie........ 166 | 15 | 19 | 17 | 34 | 14 | 64 | 29 | 7 | 43 | 35 } 1382) Black crappie........ LON) AN Oe AO a Ae? 281-25 1383) Round sunfish........ 1S cea eee 23 0 ISS) IRerelke IES, Go uodacone 48 LW A) | DAE Niles | ZO) |) OS | tS | SO i 27 e138 7" Warmouth. a eiudel te 1224 AQ ety at a\-45 17 | 88 1391] Green sunfish........ 313 | 7 | 25 | 52 | 11 | 80 | 39 | 45 | 16 |156 | 28 1397) Lepomis minzatus..... PAWN Oe Nes eeeares| i tbule’ peck . 1399} Long-eared sunfish... .|112 2|12|)76) 4] 17 | 41 | 47 | 12 | 41 | 37 iO) Orange-spotted sunfishj174 | 12 | 25 | 34 | 20 | 21 | 38 | 38 | 24 | 60 | 30 1403 Bluegill. 5 20). Yea tie A 0s) 7s Saal ae ea eae 24 || 25 1408] Pumpkinseed .........| 85 Gi Lie GAS 5G: Ae reall eee rallies al ene |). | ea | Bottom (62 species) | = | Variable = fon Available collections nan oS 48 20 48 76 . 126 39 19 31 om 11 Zs aie 2 a Z a | § 3|/ dis 5 fe) bs} P=} | fea || = 6 | 68 | 26 NO) || a) ./100 6 | 94 16 | 84 11 | 89 60 | 40 ia cek9) 23) \ O47 8 | 92 .|100 431 g ECOLOGICAL TABLE—continued Gi ALL ILLINOIS SPECIES WITH AT LEAST TEN AVAILABLE RECORDS EACH 4 Water (97 species) |Current (49 species) A Dn | w ~» g ner q ci {e) C () oO ist g Species 2 e a leg | oe a e181 2] |slel =| * a ai aa ee Aalda| of «a g Pearce Sale Wao 6) ee -e Nae: | ores = Ss ro) ra v on 3 x po | "os Bde We eis eo) sel op | > 3 & Y 3 > e | 3 & Sole ows iO | eo) o ed OR ee 85 Ud | SY | ad 3 | G2 | Sd | ake Black-sided darter..../159 | 6 | 42 | 47 1 | 49 | 70 | 30 Cottogaster shumardi...| 16 | 55 4 | 18 Green-sided darter... .| 24 46 | 53 #46) Johnny darter........ 23a ees? 1 025.)..53° |) Lo Mmale,| (68 ||’ 32 Boleosoma camurum...|107 | 9 | 23 | 42 | 17 | 17 | 41 | 59 Seem aatter.......... 19 | 13 | 47 | 39 manded darter........| 32 | 3 | 74 | 23 18 | 89 | 11 Etheostoma jessi@..... P58 eZOR | 19e te Lo | 24. i) 12 | 830) 17 Rainbow darter....... Boappsa) 4a | 45 | tise. sa | 47 } | i] Etheostoma squamiceps | 10 | 35 | 64 : ee ote | | ; Fan-tailed darter..... 307) 9 He aah var 432 ECOLOGICAL TABLE—concluded ALL ILLINOIS SPECIES WITH AT LEAST TEN AVAILABLE: RECORDS EACH | Jordan and Evermann Nos. Water (97 species) |Current (49 species)|Bottom (62 speci q a q q xe) 2 fe) ro) Se ne) B Sey ltrs elle as; Species © 7 oy og ae 2 oie a n H a = i) i) = Sa se Ae Eley Seine 5 Ba: B72) 22) oe ci 5 & ay} a iG = as ve s s a/ Pl e|3| 2) 8/8) S| ei) a) glee Wari eetcehoa lf Sp Bertil ace Bo Sa) SS llc tes BS sill. G4 | Ai @ | oO) A) ew | DD | eee Boleichthys fustformis..| 56 Tt AD Dak 2, 21,7 33eson Weastycdantenec. wanna. 42h AP OS Te oo a White bass.........../ 56 28 |...) 8) 46 |. .l0. de. NMelllowaloaSsneean er 100 | 20 Bode on SQ et eelica Sols oll ee Sheepsiedd ter a see S02) BO | to Di 27 Wee cone aiie ei aye: Si] eae eee | | if } GENERAL SUMMARY The principal conclusions of this article may be thus sum- marized: 1. The 150 native species of Illinois fishes here recognized, are so distributed within and without the state as to indicate an unequal commingling of the faune of the surrounding territories, southeast- ern species preponderating over southwestern, northeastern over northwestern, eastern over western, and southern over northern. 2. The Illinois basin may be taken as typical, in its fish popula- tion, of the ichthyology of the whole state—occupying, as it does, a central position, including more than half the area of the state, and containing a great variety of waters and situations fit for the habita- tion of fishes, and more than four fifths of the species found anywhere in Illinois. The more important fishes of the state not known from this basin are a few distinctively northern species, most of which are peculiar to the Great Lakes, and a few southern species which do not range as far north, in this state, as the mouth of the Illinois. The ~ 433 remainder are very rare in our territory, most of them coming from the west and south, and they are extremely insignificant elements of our fish fauna. 3. Ifthe ten stream systems of the state be brought into com- parison one with another, it appears that the six larger areas, con- taining the largest streams and presenting the greatest variety of situations, are much more closely affiliated ichthyologically than are the four smaller areas. The least closely affiliated with each other and with all the rest are the Michigan district of northeastern I]linois and the Big Muddy basin in the southwest. The closest relations are those between the Illinois, the Rock, and the Mississippi. 4. Inthe absence, in Illinois, of geographical barriers to the dis- persal of fishes, the causes influencing their distribution are climatic, geologic, and ecological. As Illinois extends through 5.5° of lati- tude, differences of climate between the northern and the southern sections of the state are sufficient to affect, in considerable measure, the distribution of its plant and animal species—differences which, in its ichthyology, express themselves in the presence in northern Illinois, but not in southern, of 17 species of general northward range; and in southern Illinois, but not in northern, of 14 species of general southward range. These two groups of species meet and mingle in the great north and south rivers of the western half of the state, in an area of common occupation about fifty miles in width, from the latitude of Springfield northward; while on the eastern boundary of the state, occupied by small streams of various direc- tion, these groups are separated by an interval of about a hundred and seventy-five miles over which no representative of either group has been taken. 5. Geological limitations to the dispersal of fishes are illustrated by peculiarities of distribution in southern Illinois as related to the area of the lower Illinoisan glaciation, which 34 species evidently avoid while 35 other species enter upon it freely and inhabit it suc- cessfully. A comparison of the ecological relations of these two groups of species as represented by our collection records, shows that they are strongly distinguished by the repugnance of the first group, and the indifference of the second, to waters with a muddy bottom, collections of the first group having been made from such situations in an average ratio more than three times as great as that for the second. The waters of this region, on the other hand, are re- 434 markably and persistently turbid, never clearing themselves spon- taneously. This is owing in part to the extremely fine division of the soil, and in part to its generally acid character and the consequent lack of “granulation,’’ or cohesion of its ultimate particles in gran- ules, such as occurs in the alkaline soils of the other geological areas of the state. The surface waters of the district are soft and slightly alkaline, but contain much silica, and much solid matter in suspen- sion which it is extremely difficult to remove completely by any ordinary filtering or precipitation process. The inference is plain that it is to this condition of the waters—due to the geological his- tory of the soil of this region—that the unequal distribution of these fishes is largely to be attributed. 6. In consequence of another clearly recognizable inequality of distribution, partly coincident with the two preceding and partly in- dependent of them, two additional groups may be distinguished; one of 8 species, distributed in this state mainly through the Ohio and Wabash drainage, and the other of 27 species, distributed through the Mississippi and its more northerly tributaries. The general dis- tribution throughout the country at large of each of these two groups of species is quite varied, and offers no hint of a reason for these dif- ferences in Illinois. Two hypothetical explanations are suggested— the first presupposing different centers of population outside the state, from and towards which these species move, into and out of Illinois streams, with the spring rise, summer recession, and winter cooling of the waters, one of these centers to the west and north, and one to the east and south; and the second presupposing an organiza- tion of the fish population into more or less distinct communities of mutually. well-adjusted species, each community so adapted to its environment that members of adjacent communities can not success- fully intrude upon its territory. 7. An analysis of our statistical data of ecological distribution gives us many instances of a marked difference in preference of situation between nearly related species inhabiting the same area, the effect of which is to break the force of a competition between these species such as would prevail if they were similarly distrib- uted ecologically as well as geographically. Closely related species are, aS a consequence, often found much less frequently associated in their common territory than either is with widely unlike species of the same geographical range. Exceptions to this rule are found 435 where similar species occupy adjacent areas of distribution which merely overlap by their borders. 8. iD’ xv.) y Bt . 6 é Sica \ Distribution He re oy 4 be want of s Be} l ' cael iy Hybognathus Il A Yl, oy - th nubila 4 J 2 31 Yor f SA | \ 1k j *. 4 1 af 1 bad = 5 eat Ill. and Miss. Canal pees Drainage Canal » County Seat XXVII Distribution of Pimephales promelas ek NG t ics ~ Pi > fol v7? ae hee \ =) a Ill. and Miss. Canal see Drainage Canal . County Seat XXVIII Distribution of r yey (\\ os \ hn 1 A NW rw wn j N aaa Drainage Canal , County Seat XXIX Nee ray, Saat Distribution Pai fu) DG pad ey : . * oY e IN 4 oh TS ee Semotilus , : bh. 5 ap? atromaculatus Dae i i) Be = } b U TF eens = bel Wwe uA pay \ } Saas aS Sa lh Nm: Jil. and Mich. “WPe oe voll. a iss. Re ny " Se: We Distribution of Opsopoeodus soul. and Miss. Canal paset Drainage Canal - County Seat {~~ -2 ah YU .)e | ae CC @ e a 2} g ~ Yoeea a: ; “a a ; | ; | 5 | < re ; as TAS a 9 .----ll]. and Mich. Canal } ig ea cae SY X wh ff WW TaN XXXI Distribution of Abramis crysoleucas Pay SiS Oe es c eer snes ..---[li. and Mich. Canal wml. and Miss. Canal ..---Drainage Canal - County Seat Distribution of Cliola vigilax act cae SNES a ih ne eae ae Ill. and Mich. Canal ass NB MePireaA 2! ( vowelll, and Miss. Canal \Sj res fs Drainage Canal _ q M ToANER - County Seat C Tre We OY a Qi ia Distribution .----Il]. and Mich. Canal cull, and Miss. Canal ..---Drainage Canal - County Seat eexiVe & Distribution of of Notropis “ 4 ‘BE ey i a wr blennius pt SSP ee Sa A a Us G it Wr PSN) X XXXVI Distribution of Notropis gilberti Ill. and Mich. Canal ... Ill, and Miss. Canal ..---Drainage Canal - County Seat XXXVI an, We ak of |Z ee ed WE UE area ne \e = tg iy z Uv ot awe ey \ a us a. SY Ce S a F ___lll, and Mich. ome G pe A" ee vooulll. and Miss. Can a NG _....Drainage Canal > i oes . County Seat : eS Via SN Ne XXXVIII \ BSers I Distribution Ve of Notropis hudsonius 7S XXXIX_ Distribution of Notropis lutrensis ,— seoreees _...Drainage Canal - County Seat KL EYL Os ae asf 8 Distribution “SS eae of my'2i Notropis p whipplii Sp o--=, ie ‘ae Ill. and Mich. Canal i ~ rt Ill. and Miss. Canal ey, Drainage Canal . County Seat a ae as Den f Xa Distribution of Notropis atherinoides Wa Ill. and Miss. Canal ..--Drainage Canal - County Seat XLIV Distribution of Notropis at rubrifrons 2-7 fei a oe le , ie ma oa oe . ae pute? Ill. and Mich. Canal y an fi tg ( es Il and Miss. Canal Wey | ie sot Drainage Canal a cm iY b eo - County Seat WS aS VS Jt r, wea > M4 aM Distribution of Ericymba b uccata he a a het _uullll. and Miss. cant | ae, Drainage Canal . County Seat of Phenacobius ° we oie «™ mirabilis. / aj 2 ee rn 5 a PQ . County ae Lxv ¥ Distribution “WY of Fundulus TL bax notatus : aS Saute Wear ¥ 5 ae SEGAL | Sts aS =e Bar mee Ill. and Mich. Canal % ire: eK é ees atte ag \ , Te ..-.-Drainage Ca nal - County Sea t Rl - ‘XQ LXVI Distribution of _ Gambusia L K) == Ye eS rT x = 5 nat — € 3 u 5 Fee t. = ~ 4 an ON a2, Sine “= > mat K < ~ a \) ae i & : 0 Dr. = 4 ~ offs EY PM - oy we of fo r \ ‘f UA = S (IY ey Sn] Be © —F— eas Il. and Mich. Can eel, and Miss. Canal .....Drainage Canal . County Seat Ill. and Mic Z in e ....Drainage Canal RESINS | Distribution hn AY oe, i of ) : y Labidesthes oak sicculus ie a Ke af Yea Ee a ~ . e Siete | ca ni ay a land Mich. Canal} ia pete ( wlll, and Miss. Canal - Drainage Canal +S RIVE Distribution LXIX somes aes cael Aw Fg Ass oe \ J oo y, . V Z | Se ; 744 a J Tuy if ~ Sf? Is A = : Ae ete ey A ZA tyr) g 4 if ewe: ae ao eo ¥y ZZ \ aca er io q ny Sb 25 1 a IN. and Mi ots Mig oe lll. and ze — ....-Drainage - County 28 ea My” } a 4 TAA cele sa a Geena ns mae . a ay M7 hae Je ad ls —then nik amt bo ..-Drainage Canal ee Seat BE LXXx1 Ne at onsen RS ba ‘ of i U Es p } Pomoxis sparoides sae Ill. and Miss. Canal Sera Drainage Canal - County Seat 3 Ne LXXIl N Distribution of ba | \ ye ae QO CRU Se@) Lxxul\ Ne Wy Distribution u H of Ambloplites rupestris y P _ SEZ Ds | eS : Oe — if : 25] pee is " Ny i! : Ao ‘if i er of Chzenobryttus me TES Tf LXXIV ery HAE OY istributi Sas AL ha AVY Distribution W PSS a) oe \ ack K f Bre} gulosus LXXVI Distribution of Lepomis megalotis RS Yee Tha a HEY des: a ae ms a _-----Ill. and Mich. ca, ve + ae Il and Miss. Canal | s ede Drainage Canal \e @ . County Seat LXXVIII \ Distribution of Lepomis ty Wee Y Pst ay pallidus l= ...---Ill. and Mich. wouelll. and Miss. Canal sees Drainage Canal - County Seat UXXKIX: Distribution of Eupomotis gibbosus ye ea : 2 Drainage Canal « County Seat LXXX Distribution of Micropterus dolomieu Sa Ill. and Mich. Canal cigs Ill. and Miss. Cana! Bi Drainage Canal - County Seat eee Ee < as cS Exxel % Distribution ““S of Stizostedion vitreum is aes A | ae ; NY Sec ke hy Ss . Ue aoe a Ill. and Mich. Canal welll, and Miss, Canal ..---Drainage Canal - County Seat __... Ill. and Mich. C Se adas Ill. and Miss. C _....Drainage Canal - County Seat Ne LXXXIV \ Distribution of Perca Eee CRS e ee of i ay kee “Y ee ae pees Ill. and Miss. Canal ie 3 Drainage Canal . County Seat Pred sl GB Pre of Hadropterus A A ™ |. ce% ) rf cog ST poke AA rn, : ee Distribution LXXXVII \ of Hadropterus nal ° Canal __...Il]. and Mich. Cai _...-Drainage Canal - County Seat wuelll, and Miss. ay vA Re f ; NNR ENS a : bh Ya ie : */ ee Sy Spay, SS yan coon Et Distribution W aiaenl N of po S A Eas " Diplesion fee NOY iy p j a : ee 2 Qe as 8 A 2) V_y eh 4 =| 6 > Sj oe ae Va ( at hoe = & 7 é Ls D < (Samy Sp a d “ / Cy a4 \ inf a / y : SAQ Ls e | ...--ll. and Mich. Aloo o para =a ( ToAve® 7) 447 Se. XCOT y Distribution %* an of Etheostoma of Etheostoma Jessize nee m3 Ill. and Mich. a vowel, and Miss. Canal ..-Drainage Canal e) - County Seat oF heen A LA ue We YS? = : By Le th .----lll. and Mich. Canal X pe “Deis Vee fAveE® Ill. and Miss. Canal inage Canal County Seat XCVII Distribution “2X of Etheostoma flabellare y vod LG Re cs SS | Sy J OLY Saree _....Ill. and Mich. Canal ! aby Ni pe ls sll and Miss. Cana Sas 5 ...--Drainage Canal x bsg gave® . County Seat pIF 2 O XCIX Distribution of Microperca punctulata C > Distribution of Roccus chrysops } yee AG Are 4 a lll and Mich. Canal = aia aD ay oe of Morone — interrupta ~ Distribution Cll Aplodinotus grunniens ...---Ill. and Mich. Canal onli, and Miss. Canal ' \s OO 5 rR. 7}. ee eared Pa 5 " ARSED Tr) en pains z 7 i J Is Tr i z 2 y CHF 19) =k < r 4 Southern species (a) al Canal _._..-Ill. and Mich. Can _...-Drainage Canal snaulll. and Miss. . County Seat BULLETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL HISTORY URBANA, Ituinois, U. S. A. ARTICLE IV. Vou. VIII. FEBRUARY, 1910 THE ECOLOGY OF THE SKOKIE MARSH AREA, WITH SPECIAL REFERENCE TO THE MOLLUSCA. BY FRANK COLLINS BAKER Curator of the Chicago Academy of Sciences BULLETIN OF THE ILLINOIS STATE LABORATORY OF NATURAL HISTORY UrgBana, Iviinots; U. S. A. mov. VIII. — ARTICLE IV. THE ECOLOGY OF THE SKOKIE MARSH AREA, WITH SPECIAL REFERENCE TO THE MOLLUSCA. BY “FRANK COLLINS BAKER Curator of the Chicago Academy of Sciences ILLINOIS PRINTING COMPANY DANVILLE, ILLINOIS j 3 . : . ~~ & < . z CONTENTS. PAGE NM ee eae ee es he Sl Ree Nitin hale a Wleeg oe se bp Rade ee Oe Os 441 IMMER SETI Prd ee i he cy hd Pe Se we ee ee ne OO Oe 441 GS SeTSTEEDT Sie 2 SPR Ug cee aa ee en ee 442 IEEE IEISUL eC ARIONG a Poste ot she. ee ha vie ee eink «Wn, wh alaleimeltls Qe efocele We 442 SSE SETS IEG GRRE Seek, I Bs SCA a a eg 443 NE MCAS WEIS le Sl es eet ye kPa eee ava as pew inns a eee ae 446 pees Intermediate Ridge or Sand Spit... 256... ee ee oe teh 446 C. The East Branch of the North Branch of the Chicago River.......... 447 Prmerbiia Glemyw OodbeCachnRid ge cy., feaieiy Ss ci. wig be 6 a eos ie Seo e dawns ewes 447 Benne North Branch of the Chicago River... ... 26... asec ccc bss eee 448 PREETI SEL S oro serene eke Me a aia 's wh dian, W's (eye 018 a eee a wl Pale A ele 449 Seuaied Discussion and Comparison of Stations.............:..0ccceeeeees 449 Pe KOKICN Marsh Stations) Miatid EL. cuss. wc co cine nes oe ec ceive sisted 449 Pee ne tacermediate Ridge. Stations III to KX... ......6 5.60. e ees 452 C. The East Branch of the Chicago River. Stations XXI to XXIX..... 472 = Glenwood Beach Ridge. Stations XXX to XXXIV............... 479 E. North Branch of the Chicago River. Stations XXXV and XXXVI. .484 ITN te Neato Cee rer. tee fens coe Sac St ie «sane sides cca 'e Sed alale aisle dy 484 oi SIV Sra SS) haba 6] eters (ee re ee 487 PE ACIS CARS tis science Phila vad ee es vise ho oe Pu als ala dis Be 488 ee ot SONNE Suede Ny oon le da ete we deel swe a ova Aw ada elects 489 Meee ataiorue ot the Mollusca: .>. 2... 220.62 ee a ee ees 491 Re ire EN EP Ne aS ls oR n(n ore win em Hiebe dw as Pee Bae dhe 497 “eet ea A Nets Articte IV.—The Ecology of the Skokie Marsh Area, with Special Reference to the Mollusca. By FRANK CoLiIns BAKER. INTRODUCTION. The present paper is an attempt to place on record a minute study of asmall area with special reference to its molluscan inhabit- ants. It is believed that this is one of the first attempts to apply the ecological method, so notably used by the botanists (Cowles, 1901; Jennings, 1909, etc.), to the study of the Mollusca, although Adams (1906) and Ruthven (1904) have included this class of ani- mals in their report of the Ecological Survey of Michigan, and Pilsbry (1905), Elrod (1901-03) and Adams (1900) have made valu- able contributions to molluscan ecology. Attempts to study the mollusks of a restricted region from an ecological standpoint are, however, rare, the writer having been unable to find any papers in which these animals were studied purely from this standpoint. It was thought that an exhaustive study of the habitat relations of all the mollusks of a given area might throw some light on their specific distinctions (especially those of the fresh-water pulmonates), and the studies herein detailed seem to warrant the belief that some good results along this line have been accomplished. These are referred to under the head of taxonomy (page 489). METHOD OF STUDY. The area in question was visited once or twice a week from May 18 to September 5, 1908; some additional work was also done in 1909. Many of the stations were visited several times, and nearly all were examined twice or more. Specimens were collected from the edges of the pools and ponds as well as from the deeper parts. In the woods almost every old log and piece of rotting wood was examined, and in the dry ponds the ground was dug up in many places in search of any burrowing mollusk. All material has been carefully preserved with exact data, and now forms a part of the ecological collection of the Chicago Academy of Sciences. 441 442 It has been thought of value in this connection to list all those species of animals which have been found directly associated with the mollusks in their various habitats. Thus, if a beetle was found under bark with a mollusk it was secured and listed with the mol- luscan species found at this station. So, also, the aquatic insects were listed in connection with the aquatic mollusks. ® As an ecological survey is not complete without a knowledge of the plant societies, the more characteristic plants have been listed in connection with the various habitats. This list does not pretend to completeness, its purpose being to indicate those species of plants most intimately associated with the molluscan habitats. At the time the survey was made, a collection of the nesting birds of the Skokie region was secured for the museum of the Academy, and it has been thought of value to include a few notes on these. ACKNOWLEDGMENTS. My thanks*are due to the following persons who have greatly aided in the work of the survey: &To Dr. H. C. Cowles, University of Chicago, and Miss Carrie A. Reynolds, Lake View High School, for identifying the majority of the plants; to Mr. V. E. Shelford, University of Chicago, Mr. Chas. A. Hart, of the State Laboratory of Natural History, and Mr. J. J. Davis, Assistant to the State Entomologist, for assistance in working up the insects; to Mr. A. E. Ortmann, of the Carnegie Museum, Pittsburg, for the identification of the crawfishes; and to Mr. Frank M. Woodruff and Mr. Edward R. Ford for assistance in the determination of the birds as well as for many notes and sug- gestions on the same. The photographs of habitats have been made by Mr. F. M. Wood- ruff, of the Chicago Academy of Sciences, and the author. On each photograph the name of the photographer appears in parenthesis. ECONOMIC: CONSIDERATIONS. An area such as is herein described has a distinctly economic value, affording, as it does, both concealment and food for verte- brate life. The birds find excellent protection for their young in the thick vegetation, and abundant food is provided in the numer- ous ponds, streams and woodlands. The habitats are especially 443 favorable for a large variety of avian life. The thrushes, catbirds and thrashers find nesting sites in the large number of thorn-bushes (Crategus); the woodpeckers and bluebirds, in holes in the rotting trees; the rails, bitterns and marsh wrens find protection among the cattails; and the crows and hawks find nesting locations high up in the tall trees. Many low bushes harbor the nests of the summer yellowbird, the goldfinch and the indigo‘bird. In fact the environ- ments obtainable here are suitable for a large majority of the nesting birds of northern Illinois. Food is everywhere abundant. The ponds and streams as well as the woods and fields teem with invertebrate life (mollusks, in- sects, crustaceans), thus affording endless supplies for the sustenance of nestlings. The preponderance of insect-eating birds in this region should be gratifying to the farmers, as during the spring these birds destroy vast numbers of injurious insects—a fact which is, unfortunately, not fully appreciated by the agriculturists. The hawks and owls are also very beneficial in destroying injurious rodents. In this connection the humble snake must not be over- looked, for it is equally valuable for this purpose. A number of birds were observed to feed on crawfish and also to feed their young on this crustacean. The stomachs of the young of the green heron and American bittern contained crawfish of large size, as did also the stomachs of the parent birds. The great blue heron, green heron, American bittern, and a single specimen of the fish- hawk were observed fishing in the East Branch of the Chicago River, evidently for crawfish, which are very abundant in this stream. Stomach pellets from the screech-owl were also observed to contain the remains of crawfish. It would seem eminently desirable that in a farming district, tracts of land similar to those recorded below should be preserved, that the birds may be allowed to nest unmolested; and the agricul- turist should be impressed with the value of these animals as de- stroyers of noxious insects, especially during the nesting season. GENERAL TOPOGRAPHY. If a map of the Chicago area as it appeared during Pleistocene time be examined, the following features will be noted in the north- ern part of the region, in the vicinity of Glencoe. 444 EXPLANATION OF Fic. 1. A. Map of area surveyed—from Glencoe west to Shermerville, a distance, east and west, of three miles. The width of the map (north and south) represents one mile. 1-36. Stations studied. 37. Chicago, Milwaukee and St. Paul Railroad passing through Shermerville. 38. Chicago and Northwestern Railroad cut-off. 39. Chicago and Northwestern Railroad passing through Glencoe. 40. Chicago and Milwaukee Electric Railroad. Large trees and virgin forest. | Shrubs and small trees. UUM Swamp. @ Houses. — Roads. Small ponds and pools. Unmarked spaces indicate open fields. This map is based on the Highwood topographic sheet of the United States Geological Survey. B. Profile section from Glencoe to Shermerville (the vertical scale is much exaggerated, in comparison with the longitudinal scale). 630, 670, etc., altitudes above sea-level. East Arm of Skokie Bay. West Arm of Skokie Bay. Small bay west of Skokie Bay. Skokie Marsh. Intermediate Ridge. East Branch of the Chicago River. Glenwood Beach Ridge. North Branch of the Chicago River. BiG O Gee 8 e wt a ty ; '‘§ on, eigee ae ‘ “og : tens i) 4 Mg Tay wae A4 " ‘ £499 pe ij fi + i Ao9 ey ff? ‘\ 4 630 ws a Fy FIGURE 1. 445 A rather large bay, called Skokie Bay, extended northward for a considerable distance. It is this ancient Skokie Bay which, when the ice-sheet had retreated to such an extent that Lake Chicago (now Lake Michigan) no longer discharged its waters by way of the Des- plaines-Illinois rivers, became partly drained and now forms the region familiarly known as the Skokie Marsh. A second bay lay to the west of Skokie Bay. A glance at the cross-section on the map (Fig. 1) will show the relation of Skokie Bay to this small bay, the Glenwood ridge separating the two. It seems evident, that ata stage later than the time at which the Glenwood ridge was formed, there must have been a period when Skokie Bay was itself divided into two arms. This condition is very plainly marked in the topography of the country, the ridge between the east and west shores of Skokie Bay being one of the conspicuous features of the land- scape, especially at its highest point, overlooking the East Branch of the Chicago River. This ridge attains an elevation of twenty feet above the surface of the stream. The height of the Glenwood ridge in this area is 670 feet, or twenty feet above the ridge previously mentioned. The cross-section shows the relation of these three elevations. The view of the Skokie Marsh from the top of the highest ridge at the western edge of the town of Glencoe, is really quite picturesque, and on a bright, cool morning in early spring is sure to leave a lasting and pleasing impression. The recession of the water of Skokie Bay has left some peculiar topographic features: the bed of the bay proper (see map and section) is now the Skokie Marsh; the surface of the ridge, which divided Skokie Bay into two arms and which was probably a long sand spit, contains a large number of pools of various sizes, which are more or less dry in the summer and fall; this area is rather sparsely wooded; the smaller arm of Skokie Bay is now occupied by the East Branch of the North Branch of the Chicago River; the small bay to the west of Skokie Bay is now occupied by the North Branch of the Chicago River, while the ridge between these two - streams, which is believed to be equivalent to the Glenwood beach, is heavily wooded, with but few of the small pools so characteristic of the lower ridge to the east. The area surveyed, which is three miles long and one mile wide, is thus seen to comprise five rather distinct areas, which may be designated as A, B, C, D and E. 446 A. Skokie Marsh. (Plate VI.) A strip of low, marshy land, about one mile in width, through which a small stream flows in the spring and early summer. In late summer and fall this stream is reduced to a series of pools sepa- rated by dry land. The marsh, which is covered with water from a few inches to several feet in depth in spring, becomes dried out in the fall and the ground becomes hard and sun-cracked. The marshy area is open, for the most part, and is covered with a thick growth of cattails and other aquatic vegetation, while toward the margins a tall, thick growth of swamp grass (Calamagrostis) suc- ceeds the reeds. The marsh is dotted here and there with many small ‘“‘islands’’ composed of several species of marsh-loving trees (see Fig. 1). These “islands” are surrounded by a dense growth of cattails, which attain a height of over ten feet and are very difficult to penetrate. The Glencoe road crosses the marsh, and on either side a rather deep ditch has been made, which is filled with aquatic plants. In two places these ditches form a large, deep, circular basin, connecting the ditches and spanned by a low bridge. The stream also widens as it flows under the Glencoe road bridge, forming a wide, deep pool. In the fall these ditches become more or less dry, and the basins are reduced to small pools. B. Intermediate Ridge or Sand Spit. A triangular piece of territory about a mile wide, lying west of the Skokie Marsh. The ground is from ten to twenty feet above the surface of the stream and is well wooded for the most part. The slope on the eastern face of this ridge is very gradual, but on the west it is quite abrupt, forming a rather steep terrace bordering the East Branch of the Chicago River. Scattered throughout this area are numerous depressions of various sizes, from a few feet to two hundred feet or more in diameter. These are of varying depth, from a few inches to several feet. In the spring they are filled with water and support a varied fauna and flora, but in the summer they dry up wholly or partially. These may be termed summer-dry ponds or pools—a name which seems more comprehensive than the word swale, which is used in the eastern states. About a dozen 447 such ponds were examined in this area and careful notes were made of their biotic contents. This triangular area divides naturally into three subordinate areas: one beside the road running at right angles with the Glencoe road and between this and the Northwestern Railroad cut-off; one west of the railroad; and one bordering the East Branch of the Chicago River and separated from the second area by a field about three hundred feet in width. The first area is a few feet above the Skokie Marsh stream, the second is on rising ground, and the third is on an elevation twenty feet above the river. A large part of the southern portion of this area is cleared for grazing purposes. C. The East Branch of the Chicago River. (Plates XVII.,2, and XVIIT.,1.) This stream is quite wide in the spring, and is from one to six or more feet in depth. It occupies a little valley with a rather broad flood-plain flanked on either side by abrupt ridges about ten feet high, forming, in this part of the area, distinct terraces. The river meanders considerably and also varies in width and depth. The latter is shown plainly in the late summer, when the river is reduced to a succession of small, muddy pools, varying from a few inches to ' three or four feet in depth (Plate XVIII.,1). The river may be prop- erly termed an intermittent stream. The flood-plain varies in width from a few feet to two or three hundred feet. It is covered with swamp grass, interspersed with reeds in the lower places. Trees have invaded this area, and such species as the swamp white oak and maple are abundant on the broader portions, in some places forming large groves, or thick tangles—as where the button-bush borders the river near the south- ern end of the area in question. In several places the river spreads over the entire flood-plain, forming a characteristic bog. In most places, however, the river occupies little territory outside of its bed, except in times of very high water. D. Glenwood Beach Ridge. (Plate XXII.) This area lies west of the East Branch of the Chicago River, between this branch and the North Branch. The beach reaches 448 an elevation of 670 feet, or forty feet above the river, and twenty feet higher than the ridge on the east side of the East Branch. This region is rather heavily timbered, the trees being large and the ground being covered with an accumulation of debris, showing that the area has not been disturbed by man. About a third of a mile west of the East Branch a large ridge is encountered which is very abrupt, rising suddenly from a level plain and gradually sloping toward the south until it reaches the level of the surrounding area. This was probably a sand spit extending into Skokie Bay. Small ponds, like those found in the area east of the East Branch, are generally absent, although there are several ponds and semi-marshy spots at the foot of the sand spit mentioned above. Several small streams drain into the East Branch during the spring, but aside from these, this area is quite free from summer-dry ponds, owing, probably, to its greater elevation and the absence of large depres- sions in which water might gather. To the south, this territory is cleared for pasture and farm land, and the same may be said of the areas bordering the Shermerville road, which cuts through this portion of the region. Bordering the river to the north, the ground is lower and forms a wet, marshy area in spring. This is especially true of those portions of the terri- tory to the north of the Glencoe road. E. The North Branch of the Chicago River. (Plate XVIII, 2.) This stream, which is not of an intermittent character as is the East Branch, is from twenty to thirty feet in width and is quite deep. It flows through a low area, the banks also being low, just a foot or so above the stream, and the territory on either side is swampy and reed-grown. East of the St. Paul railroad bridge, the river forms an extensive arm at the foot of the railroad embankment, which is marshy and supports a fauna different from that of the river proper. The river flows through the village of Shermerville and is becoming contaminated with sewage, like the larger stream at the southward. This area was found to be very poor biologic- ally. 449 SEASONAL COMPARISONS. The area herein discussed is typical of many in the middle west, especially in those states bordering the southern part of Lake Michi- gan. It is typical also of those areas in which the volume of water fluctuates through the seasons of the year as well as in the same season in different years. In spring, there is an abundance of water in all the streams and ponds, and every depression in the woods (as shown in Plate XVI.) is filled with water and supports some kind of animal life. Spring conditions are shown in plates XVII., XVI.,2, XX., XXIII., and XVIII.,2. In the fall the water evaporates, either en- tirely or to such an extent as to leave only small pools here and there. This condition is shown in plates XVII.,1, XVIII.,1, and XXIV.,1, which should be compared with the photographs of the same habitats in spring. The difference in one year as compared with another may be seen by comparing plates XVII.,1,and XXIV.,1, which were taken Sep- tember 5, 1908, with plates XVI. and XXIII., of the same habitats, taken September 10, 1909. It will be recalled that the year 1908 was much drier than 1909, this difference in precipitation causing a marked effect on the summer-dry ponds of this area. The year 1909 has, therefore, been much the more favorable year for inverte- brate life in these ponds and streams, owing to the less rigorous conditions of the environment. The effect has also been notably different on the vegetation, which was much more luxuriant in the fall of 1909 than at the same period in 1908. The five areas just described break up into a number of more or less distinct stations, the biota of which differ more or less. These stations will next be taken up in detail. Their positions may be ascertained by consulting the map. A. SKOKIE MARSH. (Stations I anp II.) STATION I. (Plate VI.) Skokie stream and tributary ditches. This stream was once a tributary of the East Branch, but it now ceases to exist at a point southwest of Glencoe. It is an intermittent stream, in the spring 450 being about five feet in width and from knee to waist deep. In cer- tain spots, as at the bridge over which the Glencoe road passes, it widens to form a pool twenty feet in diameter and from six to eight feet indepth. The ditches are about five feet wide and two or three feet deep. In two places (1*) the ditches form wide pools ten or fifteen feet in diameter and six to ten feet in depth. The characteristic plant life is as follows: Chara sp. In the deep pool. Polygonum muhlenbergii. In the ditches in a few inches of water. Sagittaria latifolia. In shallow water. Iris versicolor. In shallow water. Sparganium eurycarpum. In shallow water. Typha latifolia. On edge of pool. Salix longifolia. A heavy clump bordering the deep pool, north of the Glencoe road. The animal life observed was as follows. Mo.Luusks (FLUVIATILE SPECIES). Musculium partumewm. Physa gyrina. Planorbis trivolvts. Segmentina armigera. Lymnea reflexa. INSECTS. Limnotrechus marginatus. Water-strider. Corixa interrupta. Water-boatman. Notonecta undulata. Back-swimmer. Hydroporus undulatus. Diving beetle. Dytiscus larva. Larva of diving beetle. Culex sp. Mosquito. Libellula basalis. Dragonfly (adult). Anax junius. Dragonfly (nymph). Zattha fluminea. Water-bug. LOWER VERTEBRATES. Ameturus melas. Black Bullhead. Esox lucuus. Pickerel. Rana pipiens. Leopard-frog. Natrix grahami, Water-snake. STATION IT. (Plates VII. and VIII.) The open marsh. Itisaboutamilein width. In the spring the whole surface is covered with water which is from a few inches to 451 several feet indepth. In the late summer and fall this area is either entirely dry or with only a few shallow pools distributed over the surface. Scattered over the marsh are numerous forest islands from fifteen or twenty feet to over two hundred feet in diameter. Some of these are irregularly round in outline; the largest ones, however, are of an oblong shape. There are three distinct plant societies in the marsh, which may be characterized as follows. I. THE FOREST ISLANDS SOCIETY. Populus tremulotdes. American Aspen. Ribes floridum. Wild Black Currant. Salix longifolia. River-bank Willow. iW THE TYPHA LATIFOLIA SOCIETY: Cattails surround the forest islands, often reaching a height of ten feet or more, presenting an almost impenetrable jungle. In several places small areas of cattail islands occur, and the ditches and streams are lined with Typha. III. THE IRIS VERSICOLOR-CALAMAGROSTIS CANADENSIS SOCIETY. The greater part of the swamp is covered with these two plants, interspersed here and there with clumps of Sagittaria latifolia, Sparganium eurycarpum, Sium cicutefolium and Eupatorium pur- pureum. The bluejoint grass (Pl. VIII., 2) reaches a height of eight feet or more, affording excellent concealment for the nests of marsh-inhabit- ing birds. THE. FAUNA OF THE MARSH. INSECTS. With the addition of a few small beetles in the fall, the insect fauna of the marsh is the same as that of the ditches and stream. MOLLUSKS. FLUVIATILE SPECIES. Physa gyrina. Very abundant. Lymnea reflexa. Rare. 452 LAND SPECIES. Succinea retusa. Very abundant. Succinea avara. Less abundant. Agriolimax campestris. Abundant. No difference could be detected between the mollusk fauna of the marsh and that of the forest islands except in the distribution of Agriolimax campestris, which was found only about the trees of the islands. i BIRDS. During the nesting season the following birds are more or less abundant: Blue-winged Teal. Nesting site not located. American Bittern. Nesting among cattails. Least Bittern. Great Blue Heron. Nesting site not located. King Rail. Nesting among cattails. Virginia Rail. Nesting among cattails. Sora. Nesting among cattails. Florida Gallinule. Nesting among cattails. Marsh Hawk. Nesting in marsh. Kingbird. Nesting on forest islands. Traill’s Flycatcher. Nesting on forest islands. Bobolink. Nesting on border of marsh. Dickcissel. Nesting on border of marsh. Red-winged Blackbird. Nesting in marsh. Swamp Sparrow. Nesting on border of marsh. Song Sparrow. Nesting on border of marsh. Grasshopper Sparrow. Nesting on border of marsh. Leconte’s Sparrow. Nesting on border of marsh. Field Sparrow. Nesting on border of marsh. Savannah Sparrow. Nesting on border of marsh. Catbird. Nesting on forest islands. Short-billed Marsh Wren. Nesting in marsh. Long-billed Marsh Wren. Nesting in marsh. B. THE INTERMEDIATE RIDGE,OR SAND SPER. (Stations ITI-XX.) (Plate IX.) A low, wet area, on the western edge of the Skokie Marsh. It is well wooded, many of the trees being of large size. A rather wide opening extends diagonally through this area, and is occupied by a summer-dry pond. In the spring the pond is from one to two feet 453 in depth and there are several small streams which flow through the wooded portion, in which there are also many small pools in depres- sions of greater or less size. These afford good habitats for a num- ber of mollusks. The flora of this region comprises a number of distinct plant societies which may be classed as follows. (1). That of the central nucleus, the pond, which provides a habitat for Typha latifolia. Cattail. Iris versicolor. Large Blue Flag. Asclepias tncarnata. Swamp Milkweed. (2). That at the edge of the pond, which is marked by the presence of Salix longifolia. River-bank Willow. Ulmus americana. American Elm. Quercus bicolor. Swamp White Oak. This plant society is closely encroaching upon the first society, and will ultimately exterminate it by invading the entire area. (3). The large forest-trees form a distinct society which follows closely upon the society mentioned above. The trees are of large size, showing that the area has been untouched by man. The fol- lowing species comprise the dominant types: Ulmus americana. American Elm. Tilia americana. Basswood. Crategus punctata. Large-fruited Thorn. Crategus mollis. Red-fruited Thorn. Corylus americana. Hazelnut. Quercus bicolor. Swamp White Oak. Carya ovata. Shellbark Hickory. (4). The ground beneath the forest growth is carpeted with low- growing plants, among which the following species are conspicuous: Arisema dracontium. Green Dragon. Campanula americana. Tall Bellflower. Cicuta maculata. Water Hemlock. Osmorrhiza longistylis. Smoother Sweet-Cicely. Rudbeckia laciniata. Green-headed Coneflower. The entire area is an excellent example of plant succession. The poison ivy or poison oak (Rhus radicans) grows luxuriantly on the western edge of this area. (2) 454 STATION III. This includes the pond, and also the ditches within this region. INSECT LIFE. Limnotrechus marginatus. Water-strider. Corixa tnterrupta. Water-boatman. Notonecta undulata. Back-swimmer. Culex sp. Mosquito. Zattha fluminea. Water-bug. Libellula basalts. Dragonfly (adult). MOLLUSKS. FLUVIATILE SPECIES. Musculium partumeium. Occasional. Physa gyrina. Very abundant. Segmentina armigera. Very abundant. Planorbis trivolvis. Common. Lymnea reflexa. Common. LAND SPECIES. Succinea retusa. Common. Succinea avara. Occasional. STATION IV. A small stream which drains from ditch beside Glencoe road into the center pond. Also, hollows in the wooded area which are filled with water in the spring. In the fall, all of these habitats are dry, and the dead shells of mollusks may be sa scattered over the surface or under dead leaves. MOLLUSKS. FLUVIATILE SPECIES. Spherium occidentale. Very abundant. Aplexa hypnorum. Very abundant. Physa gyrina. Occasional. Segmentina armigera. Very abundant. Planorbis parvus. Rare. Lymnea caperata. Occasional. Lymnea parva sterkii. Rare. LAND SPECIES. Succinea retusa. Common. Succinea avara. Occasional. 455 STATION V. The wooded area. The ground beneath the trees is covered with leaves, dead twigs, old logs and other wood debris, which af- ford cover for the following species of land shells: Succinea ovalis optima. Plentiful. Succinea avara. Plentiful. Zonttoides arboreus. Common. Vitrea hammonis. Rare. Polygyra fraterna, Very common. Polygyra albolabris. Rare. Polygyra thyroides. Very common. Pyramidula alternata. Common. The larger Polygyras appear to frequent the base of large trees, while the smaller species are common under the forest debris and leaves. Succinea ovalis is plentiful under old leaves. Pyramidula alternata and Polygyra fraterna prefer to hide under “started”’ bark on dead stumps and logs, in company with the large beetle Osmoderma scabra. Of twenty-one specimens of Polygyra thyroides, five individuals had a pronounced denticle on the parietal wall. The specimens of Succinea ovalis optima vary greatly in the height of the spire and in the width of the last whorl. ANIMALS ASSOCIATED WITH THE MOLLUSCA. INSECTS. Osmoderma scabra. Beetle; under bark. Melanotus communis. Beetle; under bark. CRUSTACEA, Cambarus blandingi acutus. Crawfish. LOWER VERTEBRATES, Eutema sirtalis. Garter-snake. Storeria occipitomaculata. Storer’s Snake. BIRDS. Red-headed Woodpecker. Northern Flicker. Chimney Swift. Blue Jay. Crow. 456 Cowbird. Young; in yellow warbler’s nest Song Sparrow. Indigo Bunting; nesting. Northern Yellow-throat. Yellow Warbler; nesting. Red-eyed Vireo. Catbird; nesting. Brown Thrasher; nesting. Wood Thrush; nesting. American Robin; nesting. STATION VI. Clay hole about twenty feet in diameter in woods on west edge of Skokie Marsh, north of Glencoe road. The pool is almost circular in outline, but a ditch-like depression has been formed on the southwest edge, which extends irregularly for some forty or fifty feet. There is no vegetation in or about the pool. Physa inhabited the pool by thousands, all, however, being immature. During a visit in July they were observed to form a dark border about three inches in width entirely around the pool. In the ditch-like outlet fully adult Physas were found, as well as Planorbis. Only two species were found, the Physa being by far the most abundant. These were Physa gyrina, Planorbis trivolvis. During the summer and fall, the ditch-like outlet is dry. In the clay pit no Planorbes were found, and only immature Physa. In the ditch-like depression were the dead shells of Planorbis and of adult Physa. Old shells of the latter were marked with four well-defined varices, indicating rest periods. rd STATION VII. (Plates X., XI. and XII.,1.) A marshy pond about three hundred feet in greatest diameter, west of the Northwestern Railroad cut-off. The pond is roundly — ovate in shape. In the spring the water is from one to three or ~ four feet in depth, but in late summer and fall the pond is reduced — to a number of isolated pools here and there and a small wet area — in the center. . 4 FIGURE 2. Diagram showing relation of characteristic vegetation of Station VII. Thefzonal arrangement is*notable. @ Typha latifolia. o Iris versicolor. A Sagittaria latifolia. Y Salix longifolia. C Crategus, Pyrus and Viburnum. O Quercus, Carya, Ostrya and Populus, the oaks predomi- nating. The vegetation is divided into a central area and more or less distinct concentric zones of plant societies (Fig. 2), which may be described as follows. (1). A nucleus of cattails, Typha latifolia. (2). First zone, a wide expanse of reeds, [rts versicolor, inter- spersed with Sagittaria latifolia and Sparganium eurycarpum. (3). Second zone, consisting of bush-like trees, as follows. Crategus punctata. Large-fruited Thorn. Crategus tomentosa. Pear Thorn. Crate@gus coccinea. Scarlet Thorn. Pyrus coronaria. American Crab-apple. Viburnum lentago. Nanny-berry. Salix longifolia. River-bank Willow. 458 (4). Third zone, the forest proper, containing Quercus macrocarpa. Mossy-cup, or Bur Oak. Populus tremuloides. American Aspen. Ostrya virginiana. Hop Hornbeam or Ironwood. Quercus bicolor. Swamp White Oak. Carya ovata. Shellbark Hickory. The western end of the pond is free from reeds, is very shallow, and supports the following marsh-loving plants: Proserpinaca palustris. Mermaid-weed. Ranunculus multifidus. Yellow Water-Crowfoot. Sium cicutefolium. Hemlock Water-Parsnip. Ranunculus multifidus covers the bottom of the pond every- where, in the deeper as well as in the shallower portions. The invertebrate life of this station is quite varied*. The fol- lowing species were observed. INSECTS. Limnotrechus marginatus. Water-strider. Corixa tnterrupta. Water-boatman. Notonecta undulata. Back-swimmer. Zattha fluminea. Water-bug.t Libellula basalis. Dragonfly (adult). Hydroporus undulatus. Diving beetle. CRUSTACEA. Cambarus blandingi acutus. Crawfish. MOLLUSKS. Molluscan life was quite abundant in the pond. Lymne@a was found plentifully on dead pieces of cattails and reeds, many having hibernated on the stems of the reeds, two to four inches above the water; other individuals were found in the water attached to the submerged base of the cattails. The Lymneas were not found in open patches of water where no cattails grew. Planorbis occupied the same habitat as Lymne@a. Physa was rare in this area. Suc- cimea was plentiful on the stems of cattails near the water. Seg- *The vertebrate life of stations VII-XVII, is listed on page 468. +This water-bug preys upon mollusks. Mr. B. F. Isely, of Tonkawa, Okla- homa, has observed it feeding upon Physa in an aquarium, large numbers of the snail being eaten. ‘ Nee ae ee ey | a en a, ee | th es ae 459 mentina, as well as Musculium, was common in open spaces in the pond. The following species were secured. FLUVIATILE SPECIES. Musculium partumeium. Common. Physa gyrinma. Common. Segmentina armigera. Common. Planorbts trivoluis. Common. Lymnea reflexa. Common. LAND SPECIES. Succinea retusa. Common. STATION VIII. Woods surrounding Station VII. The ground is high and dry, the trees are rather far apart, producing an open woodland effect. The ground is covered with dead leaves, rotting logs and stumps, and the various debris found in such a habitat. The ground about the pond is quite high and the slope pondward is rather abrupt. Polygyra albolabris was found in fair numbers in holes in logs and stumps and under old logs; Polygyra fraterna was common under logs and ‘“‘started’’ bark; the smaller land snails were plentifully distributed in old stumps and on chips and other small debris; while Succinea ovalis was common under dead leaves in small hol- lows. Zonitoides was plentiful under “started” bark. The following species were secured. LAND MOLLUSKS. Polygyra albolabris. Occasional. Polygyra fraterna. Common. Pyramidula alternata. Rare. Agriolimax campestris. Common. Zonttoides arboreus. Common. Succinea avara. Rare. Succinea ovalis. Common. INSECT LIFE. Ceuthophilus sp. Cricket; under log with land shells. Pterostichus permundus. Beetle; under log with land shells. 460 STATION IX. A small pool to the southeast of Station VII, and connected with that habitat by an area of low swampy ground, forming a depression in the high ground surrounding Station VII. Area about fifteen by twenty-five feet. The vegetation is the same as that of Station VII. This station is carpeted with Ranunculus multifidus. Yellow Water-Crowfoot. Proserpinaca palustris. Mermaid-weed. The following mollusks were observed, Physa gyrina being the predominating species. FLUVIATILE SPECIES. Spherium occidentale. Rare. Musculium partumetum. Common. Physa gyrina. Abundant. Planorbis trivolvis. Common. Segmentina armigera. Common. Lymnea reflexa. Rare. LAND SPECIES. Succinea retusa. Common. Agriolimax campestris. Common. Lymnea reflexa is a migrant from Station VII. STATION. Xs / A small pond about thirty feet in diameter, almost circular in outline, two hundred or more feet from the larger pond (Station VII), and connected with that station by a narrow stream of water. The pond hole is from six inches to two feet indepth, and the bottom is composed of soft, tenacious, clayey mud. In the spring the hole is filled with water, but during the summer and fall the water evaporates, leaving the mud in hard, irregular cakes, the cracks between being filled with vegetation. The mollusks find a retreat in these cracks, into which they crawl and estivate. An epiphragm is formed, as in the helices, and many individuals are thus enabled to survive the dry summer, to be revived in the late fall when the rains begin, thus providing for the perpetuation of the species. Physa gyrina is the most abundant species in this station, the dead 461 shells being scattered over the mud and in the cracks in endless pro- fusion. Only about three per cent. of the shells contained living animals. . The vegetation of this station is as follows. On the Dry Bottom. Ranunculus multifidus. Yellow Water-Crowfoot. About the Border. Iris versicolor. Large Blue Flag. Crategus punctata. Large-fruited Thoriu. Tilia americana. Basswood. Ulmus americana. American Elm. Mollusks as listed below were obtained. FLUVIATILE SPECIES. Musculium partumeitum. Common. Physa gyrina. Very abundant. Segmentina armigera. Rare. LAND SPECIES. Succinea retusa. Rare. INSECTS. Notonecta undulata. Back-swimmer. Corixa interrupta. Water-boatman. Zaitha fluminea. Water-bug. STATION XI. A small stream, dry insummer, extending from Station X,in a curved direction, to the railroad embankment. The bed of the stream is about a foot in width, but in the spring the water covers the area to a width of from two to five feet. The following plants were noted in the immediate vicinity: Onoclea sensibilis. Sensitive Fern. Ribes floridum. Wild Black Currant. Crategus punctata. Large-fruited Thorn. Carya ovata. Shellbark Hickory. Sium cicutefolium. Hemlock Water-Parsnip. Quercus bicolor. Swamp White Oak. Caltha palustris. Marsh Marigold. Anemone canadensis. Canada Anemone. 462 Mollusks of the following species were secured, all fluviatile: Spherium occidentale. Rare. Musculium partumetum. Common. Segmentina armigera. Common. Aplexa hypnorum. Very common. Physa gyrina. Common. Lymnea caperata. Common. Lymnea reflexa. Rare. Lymnaea reflexa is undoubtedly a migrant from Station VII, prob- ably floated down during high water. But two specimens were found after a careful search. STATION XII. Woods bordering Station XI. The ground is low and conse- quently wet in spring. Swccinea ovalis was observed on leaves of various plants, four to five feet from the ground. It was also found : under dead leaves. In summer this area is dry and the ground is quite hard. The following land mollusks were secured: Succinea avara. Rare. Succinea retusa. Rare. Succinea ovalis. Common. Polygyra thyroides. Uncommon. Polygyra fraterna. Common. OTATION 2 Lie Wet portions of woods connecting stations XII and XIV, evi- — dently fed by overflow from Station XIV. Vegetation the same as that of Station XI. The following species of mollusks, all fluviatile, were secured. Of the first three species, the Lymnaea was the least abundant and the Aplexa the most abundant. Spherium occidentale. Common. A plexa hypnorum. Very common. Lymnea caperata. Uncommon. Planorbis exacuous. Rare. STATION XIV. (Plates XII.,2, and XIII.) A small pond about thirty feet in diameter, rather pyriform in shape. The water is knee to waist deep in the spring, but in the 463 fall it is reduced to a small area in the center. The plant societies here form into zones, as in Station VII, though not with the same regularity (Fig.3). There is a central portion (see Pl. XII.,2) which SS O96 = aes (6) 2 H852 Pos waht ot) Ta & ° pe®, ° bi & # ire s s ages x KKK 302 Coat ae # x * RG? SO a0 0° tela, KKK y C20 S Oo, oN KKK ® Ky 285 99,be * 3K Kor? (6) o, K KR 00 9 P on Nod erase” oS Ch Fur * * 302," 6, 66 \ ont. * on 5 0 meaty tei St a O 25 020, fo) = ° eye a oo” oy, E fo) at le ee. Derauta aa eee oP fa) S oO © 0000890 fe} QO '1P fe) FIGURE 3. Diagram showing relation of characteristic vegetation of Station XIV. The arrangement of Typha and Cephalanthus in distinct asso- ciations is noteworthy. Cephalanthus occidentalis. Typha latifolia. Iris versicolor. Quercus. Carya. Populus. Ulmus. WuUnOoO @ * is open and free from vegetation. The north side and west end of the pond are occupied by button-bush. The edge is bordered by a zone of Iris. There is a zone of cattails (Typha latifolia) at the south side; the east end is shallow and is filled with swamp grass. The following trees occupy the area surrounding the pond: Quercus bicolor. Swamp White Oak. Cephalanthus occidentalis. Button-bush. Salix longifolia. River-bank Willow. Populus deltoides. Cottonwood. Populus tremuloides. Trembling Aspen. Ulmus americana. American Elm. Carya ovata. Shellbark Hickory. 464 Animal life was fairly abundant, the invertebrates being as follows. INSECTS. Limnotrechus marginatus. Water-strider. Corixa interrupta. Water-boatman. Notonecta undulata. Back-swimmer. Zaitha fluminea. Water-bug. Tropisternus dorsalis. Water-beetle. Cybister sp. Larva of water-beetle. Sympetrum rubicundulum. Dragonfly (nymph). Libellula basalis. Dragonfly (adult). Anax juntus. Dragonfly (nymph). MOLLUSKS. FLUVIATILE SPECIES. Physa gyrina. Abundant. Segmentina armigera. Common. Lymnea reflexa. Rare. LAND SPECIES. Succinea retusa. Rare. STATION XV. (Plate XIV.) An open area about thirty-five feet in diameter in the midst of a rather thick growth of trees. The ground is covered with dead leaves, dead branches and other forest debris. The forest surrounding the area includes the following species: Quercus bicolor. Swamp White Oak. Carya ovata. Shellbark Hickory. Ulmus americana. American Elm. Under the leaves and in cracks in the dry earth the following mollusks were found. FLUVIATILE SPECIES. Spherium occidentale. Common. Physa gyrina. Very rare. A plexa hypnorum. Common. Lymnea caperata. Rare. LAND SPECIES. Succinea avara. Rare. 465 During the spring this area is very wet, forming a miniature pond, a few inches in depth, but in the summer and fall it is dry and sun-baked. STATION XVI, (Plate XV.) An oval depression on the highest portion of the intermediate ridge, about one hundred feet in longest diameter. The center of the pond is filled with cattails, about which is a zone of grass and aquatic plants. The pond is edged with bushes and bush-like trees, while the forest proper succeeds this formation. There are thus four different kinds of plant societies, or three zones surrounding a Bowes Oo O SySES oO Me Siglo 1e) ws S 2040. S (@) ° : oO Poo 6 o Bye OT ree oO 4 re SC OO +o ae 7% oO e 4,9 16) + ¢ brj06 ar he 0 0 ARE Fy Se Tertegons rots hats o ) ogo ote OF fet o'nty Oot xt eet te oe O10 COROT IE ALG hae Fup atias taste Pit 05 a o,0T. 0 10) oO 900% 000° oso ° ) O ARO OG. O. OG OR OV Om. .6 Oo FIGURE 4. Diagram showing relation of characteristic vegetation of Station acVI. Cephalanthus occidentalis. Typha latifolia. Iris versicolor. Dulichium spathaceum. Sagittaria latifolia. Quercus coccinea. Quercus bicolor. Salix longifolia. Populus tremuloides, Corylus, Hamamelis, Viburnum, ete. tmnmO bi+-o @ + central nucleus. (Fig. 4.) The plant societies may be tabulated as follows. 466 CENTRAL AREA. Typha latifolia. Cattails. FIRST ZONE. Sparganium eurycarpum. Sagittaria latifolia. Iris versicolor. Dulichium arundinaceum. Broad-fruited Bur-Reed. Broad-leaved Arrow-head. Large Blue Flag. Sedge. SECOND ZONE. This zone is confined to the east, west and north sides. On the north side the button-bush has filled the pond to the Typha society. Populus tremulotdes. Cephalanthus occidentalis. Corylus americana. Hamamelts virginiana. Viburnum lentago. Salix longifolia. American Aspen. Button-bush. Hazelnut. Witch Hazel. Nanny-berry. River-bank Willow. THIRD ZONE. Quercus bicolor. Quercus coccinea. Carya ovata. Ulmus americana. Ostrya virginiana. Swamp White Oak. Scarlet Oak. Shellbark Hickory. American Elm. Hop Hornbeam. In the late summer, the first zone becomes covered with small plants, ferns, etc., among which the following species are notable: Viola blanda. Fragaria virgimana. Ranunculus multtfidus. Onoclea sensibilis. Aspidium thelypteris. Aspidium cristatum. Sweet White Violet. Scarlet Strawberry. Yellow Water-Crowfoot. Sensitive Fern. Marsh Shield Fern. Crested Shield Fern. Ranunculus multifidus is abundant over the entire ponded area, both under water and forming a carpet on the dry border. Insect life is abundant in the spring, but is rare in the fall owing” to the almost complete drying-up of the pond. species were noted. The following 467 INSECTS. Corixa interrupta. Water-boatman. Notonecta undulata. Back-swimmer. Zaitha fluminea. Water-bug. Limnotrechus marginatus. Water-strider. Mollusks were very abundant in this pond, especially the larger species. Only a few individuals of two or three species (Musculium, Physa, Lymnea) were found in the central cattail area, the major- ity being found about the edges of the pond near the button-bushes, where they had taken refuge beneath the wet leaves and grass when the water disappeared. Under decaying logs and about the roots of the shrubs were the best localities for the majority of the species. The Lymnzas were abundant under damp vegetation at the east end of the pond (July-August). In this wet situation the Lymnzas, as well as some Physas and a few Musculiums, are able to survive the long dry summer and are ready to revive when the fall rains begin. The following species of mollusks were secured in this pond. FLUVIATILE SPECIES. Spheriwmm occidentale. Not common. Musculium partumeium. Common. Physa gyrina. Common. Segmentina armigera. Common. Planorbis exacuous. Common. Lymnea reflexa. Common. LAND SPECIES. Succinea avara. Rare. STATION XVII. A small depression about 100 feet southwest of Station XVI, thirty feet or more in diameter. The arboreal vegetation in and about this spot is as follows. Ostrya virginiana. Hop Hornbeam. Cephalanthus occidentalis. Button-bush. Quercus bicolor. Swamp White Oak. Carya ovata. Shellbark Hickory. 468 In summer and autumn this locality is dry and becomes filled — with dead leaves. Under these leaves the following bivalve — mollusk may be found in large numbers: Spherium occidentale. Very common. VERTEBRATE Lire; Stations VII—XVII. The area included in Stations VII to XVII abounds in avian life, both during migration and in the summer months, the locality — affording excellent nesting sites for the birds, a majority of which nest in the vicinity. Vertebrates were observed as follows. LOWER VERTEBRATES. The following species were found about the edges of the ponds ~ and pools: Rana pipiens. Leopard-frog. Amblystoma jeffersonianum. Jefferson’s Salamander. Hemidactylium scutatum. Scaly or Four-toed Salamander. BIRDS. American Bittern. Nesting in reeds of Station VII. Green Heron. Nesting in oak tree on edge of Sta- tion VII. Young out of nest July 29. Great Blue Heron. Sparrow Hawk. Red-shouldered Hawk. Red-tailed Hawk. Cooper’s Hawk. Yellow-billed Cuckoo. Flicker. Red-headed Woodpecker. Downy Woodpecker. White-bellied Swallow. Whippoorwill. Nighthawk. Kingbird. Wood Pewee. Chickadee. Crow. Blue Jay. 469 Red-winged Blackbird. - Nesting in Station VII. Song Sparrow. Red-eyed Vireo. Warbling Vireo. American Redstart. Yellow Warbler. Ovenbird. Northern Yellow-throat. Catbird. Robin. Wood Thrush. Bluebird. STATION XVIII. (Plates XVI. and XVII.,1.) An oval depression 80 by 125 feet in the edge of the woods east of the East Branch of the Chicago River, bordering an open field. In the spring this depression forms a large pond, two or more feet in depth, which supports a varied and abundant fauna. In the sum- mer and fall the water evaporates, leaving an open space in the woods, with dry, mud-cracked surface which is covered with dead leaves. Aquatic vegetation (excepting alge) is rare in this pond, only a few flags growing in a wet depression, subject to overflow from the larger body of water. The characteristic vegetation is as follows. In the Pond. Alge. Sp. undet. Bordering the Pond. Iris versicolor. Large Blue Flag. Cephalanthus occidentalis. Button-bush. In the Forest surrounding the Pond. Quercus bicolor. Swamp White Oak. Quercus coccinea. Scarlet Oak. Ostrya virginiana, Hop Hornbeam. The insect and molluscan species thrive well among the thick clumps of algz. The following species were secured. (2) 470 MOLLUSKS. FLUVIATILE SPECIES, Physa gyrina. Very common. Lymnea reflexa. Rare. LAND SPECIES. Agriolimax campestris. Common. The absence of Spheriide is noteworthy. INSECTS. Hydroporus undulatus Diving Beetle. Dytiscus sp. Larva of water-beetle. Notonecta undulata. Back-swimmer. Corixa interrupta. Water-boatman. Limnotrechus marginatus. Water-strider. Leucorhinia sp. Dragonfly (nymph). Libellula basalis. Dragonfly (adult). Epieschna heros. Dragonfly (nymph). CRUSTACEA. Cambarus blandingi acutus. Crawfish. STATION XIX. An irregular depression, two hundred or more feet west of Station XVII, lying in a northeast by southwest direction. This area is about one hundred feet long by forty feet wide, and is well stocked with plant life, among which the following species are con- Spicuous: Iris versicolor. Large Blue Flag. Sparganium eurycarpum. Broad-fruited Bur-Reed. The following species of trees surround the area: Ostrya virginiana, Hop Hornbeam. Crategus punctata. Large-fruited Thorn. Carya ovata. Shellbark Hickory. Quercus bicolor. Swamp White Oak. Cephalanthus occidentalis. Button-bush. During the spring this depression is filled with water to tl e depth of about eighteen inches. In the summer the water evapo- rates and the ground becomes hard and sun-baked. The mollusk B 471 bury themselves in the mud-cracks, and hide under leaves and in crawfish chimneys. The old stumps in and about this area afford shelter for several species of land mollusks. The following species of Mollusca were secured. FLUVIATILE SPECIES. Spherium occidentale. Common, Physa gyrina. Rare. Lymnea caperata; Rare. LAND SPECIES. Agriolimax campestris. Common. Zonttoides arboreus. Comme Strobilops virgo. Rare. The following were associated with the land mollusks. BEETLES. Penthe obliquata; adult. Meracantha contracta; adult. Alobates pennsylvanicus; adult. Antsodactylus baltimorensis; adult. Scotobates calcaratus; adult. Patrobus longicornis; adult. Pterostichus scrutator; adult. Alaus oculatus; larva. ORTHOPTERA. Ischnoptera sp. Cockroach (nymph). CRUSTACEA. Cambarus blandingi acutus. Crawfish. STATION XX, A small pool east of Station XVIII, extending from the edge of the woods into the open field. The pool is shallow, irregular in shape and bordered by a few scattering trees from Station XVIII, among which the button-bush (Cephalanthus occidentalis) is con- spicuous. It is dry in the summer and fall. Physa gyrina was the only animal observed, and this was very abundant. 472 VERTEBRATES IN THE VICINITY OF STATIONS XVIJ—-XX. In the triangular piece of woodland, between the river and the open field, including within its borders Stations XVIII to XX, a number of vertebrate animals were observed. REPTILIA. A large garter-snake (Eutenta strtalis) was observed nicely tucked away between a large piece of ‘‘started’’ bark and the stump of an old tree. It was discovered while pulling the bark away in afsearch for mollusks. AVES. Birds were very plentiful in this area, and were as noted below: American Bittern. Great Blue Heron. Green Heron. Cuckoo; nesting. Flicker; nesting. Crow; nesting. Bronzed Grackle. Red-winged Blackbird. Blue Jay. Cowbird. Swamp Sparrow. White-throated Sparrow. Bobolink; nesting. Chewink. Catbird; nesting. Wood Thrush. Brown Thrasher; nesting. Robin. Bluebird. C. EAST BRANCH OF THE CHICAGO RIVER. | (Stations XXI-XXIX.) ) STATION X XI. 1 | (Plates XVII.,2, and XVIII.,1.) As previously intimated, in the spring the river is quite wide and contains an abundance of water (Plate XVII.,2), but in the fall (Plate XVIII.,1) is reduced to a succession of elongated pools into — 473 which the aquatic life crowds at this season of the year. The bottom of the river is composed of sticky blue clay. The whole area is much trodden by the feet of cattle. The principal plant life of the river is as follows: Polygonum pennsylvanicum Pennsylvania Persicaria. Polygonum hydropiperoides. | Mild Water-Pepper. Tris versicolor. ~ Large Blue Flag. The Polygonum forms large masses in the shallower portions of the river. — MOLLUSKS. The molluscan fauna of the stream is quite varied, the mollusks being able to adapt themselves to the rigorous summer conditions, at which time they retreat to the small pools which are left in the deeper parts of the stream. The appended list of species is large, considering the character of the habitat. Lampsilis parva. Common. Anodonta grandis. Common. Anodontoides ferussacianus. Occasional. Spherium stamineum. Abundant. Musculium transversum. Abundant. Physa gyrina. Abundant. Ancylus rivularis. Common. Planorbis trivoluis. Abundant. Planorbis parvus. Common. The pelecypods thrive in the soft blue clay, the unionids in the deeper parts, the sphzeriids along the shore in shallow water. Ancylus rivularis and Planorbis parvus live on the stems of rushes. INSECTS. The insect life of the river is apparently the same as that in the larger ponds and pools of the intermediate ridge. The following were observed: Limnotrechus marginatus. Water-strider. Corixa tnterrupta. Water-boatman. Zattha fluminea. Water-bug. Dineutes assimilis. Water-beetle. Notonecta undulata. Back-swimmer. 474 VERTEBRATES. The river vertebrates observed were as follows: Rana pipiens. Leopard-frog. Chrysemys marginata. Western Painted Tortoise. Ameiurus melas. Black Bullhead. STATION XXII. In many places the river forms bayous of considerable depth, which are largely filled with Iris versicolor. This area, as well as certain portions of the flood-plain adjacent to the river, is subject to overflow. Physa and Planorbis are abundant in this habitat, and Lymnea parva sterkit is common on the margin on leaves and sticks, or on the bare surface of the mud. It is seldom found in the water. MOLLUSKS. Physa gyrina. Planorbis trivolvis. Lymnea parva sterki1. STATION XXIII. Small streams running into river, on west bank. These streams start from springs in the higher ground and gradually enlarge until, in several cases, a stream has been formed two or three feet in width. That there is frequently a large volume of water is shown by the depth to which the stream has cut, forming a miniature valley, and cutting away a large portion of the surrounding area. In the summer and fall these streams completely dry up. The banks on the west side of the river are more heavily wooded, thereby holding the water and storing it up in springs. Physa gyrina was the only mollusk found in these streams. STATION XXIV. (Plate XIX.) The flood-plain between the river and the terrace-like banks. The ground is low and level, and subject more or less to overflow from the river during high water. The vegetation is made up of two main plant societies—(1) the trees which have descended from the terraced banks and (2) the more natural semiaquatic vegeta- tion. The notable species of each group are as follows. 475 Vegetation characteristic of wet and swampy localities: Cephalanthus occidentalis. Button-bush. Iris versicolor. Large Blue Flag. Verbena hastata. Blue Vervain. Lobelia cardinals. Cardinal Flower. Penthorum sedoides. Ditch Stonecrop. Trees encroaching from higher ground: Carya_ ovata. Hazelnut. Populus tremuloides. American Aspen. Ulmus americana. American Elm. Quercus bicolor. Swamp White Oak. Crategus punctata. Large-fruited Thorn. Acer saccharum. Sugar or Rock Maple. Beneath decaying logs and under “started’’ bark, in depressions in the bark, in rotting stumps and in crevices, the smaller land mollusks, as well as insects, are more or less abundant. MOLLUSKS. Agriolimax campestris. Common. Zonttoides arboreus. Common. Vitrea indentata. Rare. INSECTS. BEETLES. Ceruchus piceus. Adult. Alaus oculatus. Larva. ORTHOPTERA. Ischnoptera intricata. Adult. LOWER VERTEBRATES. Amblystoma jeffersonianum. —Jefferson’s Salamander. Rana pipiens. Leopard-frog. BIRDS. The avian life was abundant, the following species being noted : American Bittern. Great Blue Heron. Green Heron; nesting. American Osprey. 476 Belted Kingfisher. Yellow-billed Cuckoo. Hairy Woodpecker; nesting. Northern Flicker. Nighthawk. Long-billed Marsh Wren. Blue Jay. American Crow; nesting. Red-winged Blackbird. Swamp Sparrow. Pheebe. Song Sparrow. Yellow Warbler. Northern Yellow-throat. Catbird. STATION XXV. A small depression about eight feet in diameter, a few feet fron the river, north of the Glencoe road. In the spring this spot 1 filled with water which overflows into the river, but in the summe and fall it becomes perfectly dry. It is bordered on the one side near the road, by a number of Crategus bushes (C. punctata), an on the other side by an open field. It is noteworthy that the mollusks are the same as those in th smaller summer-dry ponds mentioned previously. The Lymnaea 1 not found in the river. The Lymnea is the most abundant, th Physa being represented by only a few individuals. Physa gyrina. Lymnea caperata. STATION XXVI. (Plate XX.) A rather large area (several acres) of virgin forest, situate north of the Glencoe road and west of the middle branch of th river. The vegetation consists of the following trees, which are « large size: Quercus bicolor. Swamp White Oak. Ulmus americana. American Elm. Carya ovata. Shellbark Hickory. Corylus americana. Hazelnut. Tilia americana. Basswood. Crategus punctata. Large-fruited Thorn. A77 Beneath the trees the vegetation consists of bushes and ground plants, among which the following are conspicuous: Sium cicutefolium. Hemlock Water-Parsnip. Rudbeckia laciniata. Green-headed Coneflower. Cicuta maculata. Water Hemlock. Campanula americana. Tall Bellflower. Trillium sp. Wake-robin. Arisema triphyllum. Jack-in-the-pulpit. Viola palmata. Early Blue Violet. A small brook flows through this forest, and empties into the East Branch of the Chicago River. The banks of the brook are low, from six inches to a foot above the water, and are thickly lined with low-growing plants and flowers. Lymnea caperata is apparently the only mollusk which inhabits this brook. STATION X XVII. Small pools in depressions caused by heavy rains. These pools overflow into the brook mentioned under Station XXVI. The only life observed in these pools was a mollusk (A plexa hypnorum) and a leech. The mollusks were observed crawling over the dead leaves on the bottom of the pool or swimming, shell downward, on the surface of the water. The leech was found on the surface of the leaves. STATION XXVIII. (Plate X XI.) The whole area of Station X XVI is covered with old stumps and logs, all half rotten, with the bark “‘started’”’ and on many logs partly peeled off. There is also an abundance of the usual forest debris of small sticks, leaf mold, fallen trees, etc. In the spring these half-decayed relics are partly hidden by the long grass, vines and flowers which abound in this area. The logs and stumps are further ornamented by huge fungus growths. Life is very abundant in this station. The following species were noted. MOLLUSKS. Pyramidula alternata. \ Found under old logs and crawling Polygyra thyroides. J over the surface of the ground. 478 Succinea avara. On old logs, sticks, etc., above the water. Vitrea hammonts. Vitrea indentata. Helicodiscus parallelus. On old logs, in crevices and under Vertigo ovata. “started ’’ bark; also in moss. Carychium exale. Zontitoides arboreus. Euconulus fulvus. On rather dry bark on ground. Agriolimax campestris. On wet bark and leaves; in dry weather under ‘“‘started’”’ bark and under logs. INSECTS. Insects were not abundant in species, but individuals were numerous of the few species observed. These were secured under bark of rotting logs. BEETLES. Penthe obliquata. Adult. Copris anaglypticus. Adult. Elater sp. Larva. MYRIAPODA. Lithobius sp. Centipede. BIRDS. The following summer-resident birds were observed at this Station: American Woodcock. Nesting. Red-shouldered Hawk. Nesting. American Sparrow Hawk. Nesting. Screech Owl. Nesting. Yellow-billed Cuckoo. Nesting. Downy Woodpecker. Northern Flicker. Nighthawk. Crested Flycatcher. Wood Pewee. Pheebe. Blue Jay. American Crow. Cowbird. American Goldfinch. 479 Song Sparrow. Rose-breasted Grosbeak. Indigo Bird. Scarlet Tanager. Tree Swallow. Red-eyed Vireo. Cerulean Warbler. Ovenbird. Yellow-breasted Chat. American Redstart. Catbird. Brown Thrasher. Nesting. White-breasted Nuthatch. Chickadee. Wood Thrush. American Robin. Sration XXIX. A wide ditch beside road near Station XXVII. The water was tagnant and the animal life consisted of one mollusk (Physa gyrina) nd a leopard-frog (Rana pipiens). D. GLENWOOD BEACH RIDGE. (STATIONS XXX-XXXIV.) STATION XXX. Heavy woods on west bank of East Branch of the Chicago River. [he surface rises somewhat abruptly at first and then becomes evel. The area is rather heavily timbered and the ground is sovered with a large amount of forest debris. In the early spring the ground is almost carpeted with flowers such as the early blue violet (Viola palmata). The principal forest trees are as follows: Quercus bicolor. Swamp White Oak.. Ulmus americana. American Elm. Carya ovata. Shellbark Hickory. Ostrya virginiana. Hop Hornbeam. Populus tremuloides. American Aspen. Acer saccharum. Sugar or Rock Maple. 480 The following mollusks were observed: Philomycus carolinensis. Common. Polygyra albolabris. Rare. Polygyra thyroides. Common. Zonitoides arboreus. Common. Vitrea hammonmis. Common. Helicodiscus parallelus. Rare. Philomycus lives under large logs, as do also the Polygyras. The small helices are abundant under “started” bark. All of the Polygyra thyroides were dentate. VERTEBRATES. Avian life was very abundant in this station and the following species were noted: Red-shouldered Hawk. Nesting. Screech Owl. Yellow-billed Cuckoo. Nesting. Red-headed Woodpecker. Northern Flicker. Nighthawk. Crested Flycatcher. Wood Pewee. Blue Jay. American Crow. Nesting. Cowbird. American Goldfinch. Nesting. Indigo Bunting. Nesting. Towhee. ‘ Rose-breasted Grosbeak. Scarlet Tanager. Chipping Sparrow. Yellow Warbler. Nesting. Ovenbird. Catbird. Nesting. Wood Thrush. Nesting. Brown Thrasher. Nesting. American Robin. Nesting. STATION XX XI. A small pool about a quarter of a mile from the river, and ap- parently the head of one of the streams flowing into the river in the spring. The small depression is choked up with dead leaves in the 431 summer and fall. Under these leaves Aplexa hypnorum is very abundant. The bordering vegetation is the same as that surround- ing the pools mentioned under Station XXXII. The following mollusks were observed: Aplexa hypnorum. Common. Succinea avara. Rare. STATION XXXII. (Plates XXII., XXIII., and XXIV.,1.) A pond about three hundred by one hundred feet, situated on the edge of a rather dense forest of American elm, shellbark hickory and swamp white oak trees. The pond is bordered on the north by the heavy forest, on the east by the open forest, on the west by a steep ridge and on the south by an open field. Unlike the ponds previously considered, the aquatic vegetation is scant and confined to a few scattering Iris at the north end. The bottom of the pond is composed of sticky blue clay. The pond is very interesting, lying, as it does, at the very base of the steep ridge and differing so mark- edly from the other ponds of this region in the almost total absence of cattails (Typha) and other reeds. Plate XXII. shows its loca- tion at the base of the ridge and Plate XXIV., 1, shows its condition in September after a prolonged period of drouth. In the early spring, the water extends to the trunks of the trees, as shown in Plate XXIII., which was, however, photographed in September, 1909. Comparison between this plate and Plate XXIV., 1, will illustrate the effect of a dry and a wet season on the ponds and pools in this area. “Only a few species of mollusks were observed in the pond. #: At the north end, under wet leaves, in a low area subject to inundation, Ancylus parallelus was found in considerable numbers attached to the under surface of the dead leaves. The following species of trees were noted about the pond: Carya ovata. Shellbark Hickory. Populus tremuloides. American Aspen. Quercus bicolor. Swamp White Oak. Quercus rubra. Red Oak. ; Ulmus americana. American Elm. Tilia americana. American Basswood. Acer saccharum. Rock Maple. Salix longifolia. River-bank Willow (in pond). 482 Vegetation at the north end: Iris versicolor. Great Blue Flag. Cephalantkus occidentalis. Button-bush. MOLLUSKS. Musculium partumerum. Common. Planorbis trivoluis. Common. Ancylus parallelus. Common. Segmentina armigera. Common. INSECTS IN POND. Hydroporus undulatus. Water-beetle. Graphoderes liberus. Water-beetle. LOWER VERTEBRATES. The only aquatic vertebrate seen was the Western Painted Tor- — toise (Chrysemys marginata), which was very abundant. . AVES. The following birds were observed about the pond. Green Heron. Kingfisher. Red-headed Woodpecker. Flicker. Crow. STATION XX XIII. A large area in the woods, about four hundred feet north of © Station XXXII, subject to periodic inundation. The area covered, appears to be two hundred feet long and thirty or more feet wide. — The forest is quite dense, and is composed of the same kinds of trees as those recorded for Station XXXII. The wet area is sparsely covered with tall grass and reeds and other water-loving plants. Among others, the following are conspicuous: Iris versicolor. Large Blue Flag. Cephalanthus occidentalis. Button-bush. Sparganium eurycarpum. Broad-fruited Bur-Reed. The mollusks noted below were observed: Planorbis trivoluis. Rare. Succinea avara. Common. Polygyra albolabris. A few observed under logs. 483 The absence of Lymnea caperata as well as of Spherium occiden- tale and Musculium is noteworthy. STATION XXXIV. (Plate XXIV., 2.) Open fields and meadows north of the Shermerville road and west of the East Branch of the Chicago River, on rather high ground. The fields are allowed to grow grass for hay. The meadow clover (Trifolium pratense) is the most conspicuous plant, with the addition of the buttercup (Ranunculus acris) in the spring. In many places in these fields and meadows there is an abundance of old pieces of wood, small pieces of board fences, rotting stumps and other debris, under which the smaller land mollusks abound. This station yielded the following species. MOLLUSKS. Agriolimax campestris. Bufidaria contracta. Bifidaria pentodon. Euconulus fulvus. Strobilops virgo. Zonitoides arboreus. Several species of beetles and a myriapod were found asso- ciated with the mollusks, as follows. BEETLES. Coccinella 9-notata. Platynus punctiformts. Euphoria nda. MYRIAPODA. Lithobius sp. Centipede. BIRDS. The birds noted below were observed in and about the fields: Red-headed Woodpecker. Northern Flicker. Chimney Swift. Kingbird. Blue Jay. 484 Bobolink; nesting. Meadowlark; nesting. Bronzed Grackle. Field Sparrow; nesting. Song Sparrow. Barn Swallow. Brown Thrasher; nesting in Crategus bush near road. American Robin. E. NORTH BRANCH. OF THE CHICAGO RIVER. (STATIONS XXXV, XXXVI.) STATION XXXV. Swampy, ditch-like overflow (from the river) on east side of railroad embankment, north of Shermerville. The water is shallow and stagnant for the most part. Iris versicolor was the conspicuous plant. Three species of mollusks were abundant: Physa gyrina. Planorbis trivolvis. Lymnea caperata. STATION XXXVI. (Plate XVIILI.,2.) The river. No opportunity presented itself for examining the bed of this river for pelecypods. It is used for sewage purposes, and is, therefore, a difficult stream to study. Two species of fresh-water pulmonates were observed in abun- dance: Physa gyrina. Planorbis trivolvis. SUMMARY. A study ot the two appended tables reveals some suteresting facts. In Table I (terrestrial species), Station XXVIII yields the largest number of species (11), and Station V follows with eight species. These habitats are the heavy woods where there is an abundance of forest debris. The Succineas are present in the ma- jority of stations, retusa and avara being most frequently seen. The : 485 ‘small zonitoids, the pupoids and Philomycus seem to be the least widely distributed in this limited area. The last was observed in but one habitat. The typical molluscan societies and their habitat relations may be summed up as follows. In swamp with Typha or Iris. Succinea retusa, Succinea avara, Agriolimax campestris. On low ground subject to overflow. Agriolimax campestris, Polygyra thyroides, Polygyra fraterna, Pyra- midula alternata, Zonttoides arboreus, Vitrea hammonis. On higher grounds, raised above overflow. Succinea ovalis, Agriolimax campestris, Polygyra albolabris, Philo- mycus carolinensis. On dry ground. Strobilops virgo, Helicodiscus parallelus, Vitrea indentata, Euconulus juluus, Bifidaria contracta, B. pentodon. Living under ‘started ”’ bark, etc. Zonitoides, Vitrea, Strobilops, Helicodiscus, Vertigo, Euconulus, Bifidaria and Carychium. Pyramidula is frequently found under “started ”’ bark, and Polygyra albolabris haunts holes and large crevices in dry weather. Table II (fluviatile species) is also of interest. Station XXI, the East Branch of the Chicago River, yields nine species. The highest number of species from any other habitat is seven, which number was observed in Stations IV and XI. Both are summer- dry ponds. Physa gyrina is the most abundant species, occurring in alljbut six of the fluviatile habitats. The naiads are the least abundant, occurring only in the East Branch of the Chicago River. The habitat relations of the molluscan societies may be sum- marized as follows. Found in all varieties of habitat. Physa gyrina. (4) 486 In large summer-dry ponds. Physa gyrina, Planorbis trivoluis, Planorbis parvus, Planorbis exacuot s, Segmentina armigera, Musculium partumerum, Ancylus parallelus, Lymnea reflexa. "i In small pools of very transient character. Lymnea caperata, A plexa hypnorum, Spherium occidentale. In the river, which does not run dry. Spherium stamineum, Musculium transversum, Lampsilis, Anodonta, Anodontoides, Physa gyrina, Planorbis trivolvis, Ancylus rwularts. | Semiaquatic; on the edges of river and pools. Lymnea parva sterki. In brooks and overflow from river. Lymnea caperata. * * * * TIAXX UAdWOAN NOILVIS ****saroadg jo [eo], sete eee eel eeeeeewweel es we eee “eulo} ely eIABA[OG eee eeeweeleeeeeeeeeele ee ee *saprolAyy PIABAIOD “*") “sriqejoqe eIABATOg sevseeltseeeede oss + cpa paUapUL BATHE A srerereadececreeels ss 2 +“ STTOTUUIBY BOIITA Hennte|emmeeds sess SHAM] snpRuOONg trssresrdascrercende © © s sSHOTOGI SAPIOPWUOT “stiqsedurvo xeulljolsy Sevvteccce|[seccsycccs|nccccacssn|evcencavcu[nescctevse|tscessvces|sucvoucsse[nesassesac|is 0 ee . OSIIA sdopiqo1g seteescculscvevercct|sncccscsen|eevarecnesleccsnceere|esconecee| sie s : uopojued eLiepylg Vashaeende| depts tase | exate cect] Rexsnent er] (Nov. Comm. Acad. Imp. Sci. St. Petersburg, XX., 1776, p. 484.) Wildcats were formerly found throughout the state wherever _ there was extensive heavy timber, and they are still not uncommon in the heavily wooded portions in the south. I obtained the skull _ of a specimen at Olive Branch, Alexander county, in 1908. A number of them had been killed in that vicinity. Merriam says that in the Adirondacks they nest in hollow trees, making a soft bed of moss. From two to four young are produced in a litter. In thinly settled sections the wildcat often destroys the farmer’s lambs, small pigs, and poultry. Their regular food in a wild state consists of rabbits, squirrels, and other small mammals, together aie A, 570 with such birds as they can get. The early settlers of the county declare that wildcats were found in the county between 1835 and 1840, but I can get no proof of their being found later. i TIMBER-WOLF. Canis occidentalis (Richardson). Canis lupus occidentalis Richard., Fauna Bor. Amer., Mamm., I., 1829, p. 60. The timber-wolf ranged originally over all the timbered portions of the United States and the adjoining portions of Mexico and Canada. Whether all the forms found in this territory should be classified as belonging to one or more species has not been well settled. They were formerly abundant along the wooded bluffs — and the forest areas everywhere throughout Illinois, and are still — found in the state occasionally in various localities. 4 The species varies so greatly in both size and color that no exact — description of it can be given. Judging from the scanty material available, perhaps the average specimens met with in this state might be described as follows: Length, 4 feet (1220 mm.); tail, 15 inches (380 mm.). Young pups with soft woolly hair, buff to ochraceous in color, lighter below. Ears tipped with tawny ochraceous bordered with — black. q General color of adult gray, with more or less ochraceous. Color lighter below, the feet sometimes becoming nearly white. In the wilderness wolves live chiefly on rabbits and deer. The number of deer killed by them is enormous. In more civilized sec- tions of the country they take up with whatever animals they can catch and kill. Their liking for sheep is proverbial, and a bounty on wolf scalps is still offered in most parts of the state. During the years 1883 to 1905 inclusive, bounties were paid on 159 wolves © killed in Champaign county. Wolves have been reported within the county since that date, and it is not at all unlikely that a few still exist in the heavy timber along the Sangamon River and — the Vermilion. ; They den in such shelter as is furnished by caves, upturned — trees, etc. There are six to ten pups ina litter. Judging from the list of bounties paid in this county, the number in a litter here is from four to nine. a 571 PRAIRIE-WOLF; COYOTE. Cants latrans Say. (Long’s Exped. Rocky Mts., I., 1823, p. 168.) Prairie-wolves were formerly abundant throughout the prairie and plains region of the United States and Canada to the Saskatch- ewan.