BEL ooo. cc en ee On the Pielexy 4 # Re 2 Ua ie i], Oo pl) ig2° i the A¢ tie. hy dreph! ENT ENS Bae ee by QL 596 H8R532 1920 Bae ENT fe } Raw ae es on the Biology of the Aquatic Hydrophilide By E. Avery Ricumonp : ee! A kaa na: BULLETIN OF > ee (aE EORTC Celi cantar AMERICAN MUSEUM OF NATURAL HISTORY =~ | Vou. XLUL, Arr. I, pp. 1-94 | oe New York nee : Issued 'SEP 27 1020 Me ad LL. Buchanan BULLETIN AND MEMOIRS OF The American Museum of Natural History Frank E. Lurz, Editor The following are the more recent papers on INVERTEBRATE Zootoey. Orders should be addressed, Library, The American Mu- seum of Natural History, 77th St. and Central Park West, New York City. 142. Ants Collected in British Guiana by the Expedition of The American Museum of Natural History During 1911. By William Morton Wheeler, 1916, Bulletin, XX XV, Art. 1, pp. 1-14. 15c. 143. New and Noteworthy Brazilian Muscoide Collected by Herbert H. Smith. By Charles H. T. Townsend, 1916, Bulletin, XXXYV, Art. 2, pp. 15-22. 10c. 144. Parasitic Muscid Larve Collected from the African Elephant and the White Rhinoceros by the Congo Expedition. By J. Bequaert, 1916, Bulletin, XXXV, Art. 21, pp. 377-387, 3 text figures. 10e. 145. The Geographic Distribution of Bombide (Hymenoptera), with Notes on Certain Species of Boreal America. By Frank E. Lutz, 1916, Bulletin, XX XV, Art. 26, pp. 501-521, 2 text figures. 20c. 146. Descriptive Catalogue of West Indian Cicindeline. By Charles W. Leng and Andrew J. Mutchler, 1916, Bulletin, XX XV, Art. 36, pp. 681-698, Pl. xm, 5 text figures. 20c. 147. Three New Species of Evaniide. By Charles T. Brues, 1916, Bulletin, XXXYV, Art. 39, pp. 717-720, 1 text figure. 10e. 148. New Species of the Bee Genus Andrena in The American Museum of Natural History. By Henry L. Viereck, 1916, Bulletin, XXXV, | Art. 42, pp. 729-732. 10c. 149. Insects of Florida (Part IV. Lepidoptera). By John A. Grossbeck (Edited by Frank E. Watson), 1917, Bulletin, XX XVII, Art. 1, pp. 1-147, 1 text figure. $1.25 150. New Acarina. Part IJ —Descriptions of New Species and Varieties from Iowa, Missouri, Illinois, Indiana, and Ohio. By H. E. Ewing, 1917, Bulletin, XX XVII, Art. 2, pp. 149-172, Pls. r-1v. 50c. 151. Supplement to Preliminary List of the Coleoptera of the West Indies. By Charles W. Leng and Andrew J. Mutchler, 1917, Bulletin, XXXVI, Art. 5, pp. 191-220. 2ZaC. 152. Second Paper on Brazilian Muscoidea Collected by Herbert J. Smith. By Charles H. T. Townsend, 1917, Bulletin, XX XVII, Art. 6, pp. 221-2338. 10c. 153. New Species of Bees of the Genus Andrena, from Equatorial Africa, in The American Museum of Natural History. By Henry L. Viereck, 1917, Bulletin, XX XVII, Art. 7, pp. 285-239. 10c. 154. Contributions to our Knowledge of the Bee Genus Perdita Smith. By Henry L. Viereck, 1917, Bulletin, XX XVII, Art. 8, pp. 241-242. 10c. 155. Notes on West Indian Syntomide and Arctiidze (Lepidoptera). By Wm. T. M. Forbes, 1917, Bulletin, XX XVII, Art. 14) pp. 339-345, 5 text figures. 10ce. 156. Effect of Humidity on Pupal Duration and on Pupal Mortality of Drosophila ampelophila Loew. By Adolph Elwyn, 1917, Bulletin, XXXVII, Art. 15, pp. 347-353, 1 text figure. 10e. 157. North American Cicadellide in the Collection of The American Mu- seum of Natural History. Subfamily Cicadelline. By Chris E. Olsen, 1918, Bulletin, XX XVIII, Art. 1, pp. 1-6, 1 text figure. 10e. 158. Insects of Florida (Part V. The Water Beetles). By Charles W. Leng and Andrew J. Mutchler, 1918, Bulletin, XX XVIII, Art. 3, pp. 73-116, 2 text figures. 40c. ais pie ie Pon eN OF THE AMERICAN MUSEUM OF NATURAL HISTORY VOLUME XLII, 1920 59.57, 68H Article I—STUDIES ON THE BIOLOGY OF THE AQUATIC HYDROPHILIDE/ By E. Avery RICHMOND pie Plates I to XVI CONTENTS PAGE Tl. — TESA OIE OTCON Ra avea chee cls: oro, cere cca eicecs cle eaneMe Ui re Lb fire ner eie ston ALEAaC REA a eae 3 [SYS GOTHIGN ca) apesegcia coke a crete ee eee edhe lee eecees aul OPE DR Rn a c 3 Eerie stom COlle Chin Me wan ree Nn Nie ot merce ce UNS Ayal WE Rn Ny 8 LAH IRGGIST ON LRREUT CANE? as ae Ae LARe CES DRS ERM seein ETN CHE it Sete em eae 2 9 Mee Gran erSTtORY AND MDLOLOGYA.. «cseates ok dec eae AMEN Ooi aN ae, es ae aE 10 Breuer SUA yer rete rte Oe ear ts AIG LI ake mle ARI tien, et 10 bared REPU GSTIR CF EE CEES WSCC meres elisa sane Umer ayte Mac eu aleaen Mase go vos 12 General Characters of the Family (Immature Stages).................. 14 General Characters, Life History, and Biology of the Forms Studied...... Uy ihc JEUGl op olivia tnveer cath one creme Og o omia cee he Sea a ReneS Cie RET ene 7 EL CIOILONIISH (PEL ey rest ey snares ecrays ec bairh arias cabanas, ou cae e neers ee 17 1 Bis AC UISIFTESE eis pie Bm ee RTS ato eae EE CERRO SORES PORT ages eat 18 BETES CLOUILECILSE Oe se se AEBS ee Po Ev iets eae ee ENS eR NN A 20 PPOTINITIC STITT CMe PoP R eM Penk se aaa arate ats coe seme eri Je eet st 20 | FDS LURE oo Pete McA tT i eee PRT A EAP aah eV Se ee 21 LE ES COLO Ty OM PIC EURO cE oe ate EA ea aN Py ee Takin, (eo coal ele 21 Biv, LEICA RST TD 5M Cy whe One ela eo a NS cactace 1 CH noe Rt ee aE Ra aera 21 (GI REE OH a (CTPA ILE) cerned corel ea et eek ee eae RR LSE eA pt en Pal OD MOG LADS oc eouee oe OETA aL AL EL ee 22 JE Gaahtaei ia). (WEA IN ep Sees oat Meelled ATi oro ete San ec Re rE 8 i 8 DEP ae 24 ELEM CTUIES LUCTUUC One en Te amr ee ee a ee ee: Peo ay oe 24 PEL LOSE DEIN our ey ed snus rnb ce incabmna ier Me ind yeti tl Me Dil PEEL CLEGG INGOT Oem He Sern emt km, e aeN eh Ue Lond on 27 EMU OLOCLOU Sm (UAVS eapereertg sateen: pric aces Aras eames che) Sih HI. squamifer...... BTA fer hod tet Sis pea Ent aaa MA were eo 1 s Me. nya j Z Bulletin American Museum of Natural History {Vol. XLIL 6: Sphercheinges 5. 05.600. ae 6 Veer 2 ee ee 30 Uo lskyobasyooultinee,.s.o50n5056.0%40 ROS ror ie Ae G8 bs Ais 2 2 o bl Aydrophilus (Pl. VA) os sin 9 0s sas eu le Eee ol EF ODtUSGLUS Soe dev Oh ES he, De 31 Tropisternus (Pl. VIL) ooo. ee © oe One a eee FE Qlaber oR nn he oe Cee 35 Ps SUDLRUIS See aE eee 39 Hydrous (RIVE) fen bien oe ds okie ee eee 39 ED LGN QUOTAS © 2 Beas ee eee Oe Oe eee 40 Si (Ey drobling ck. i ene oe ne eo eee 1 ae ae Laccobtus (Pl. EX) .)s2.03 2 ee eee 43 Ds SOGUAS sios8 Goce Be OS is Mn OEE Eee 43 Béerosus (Pl ens Se ee eee 47 BB OT OQTUTUS 4s sali ven se rag Sarena Oe Sa eS B.. SUrQHUS oes So a in ee 51 Chebarthrra.o5 5 renga ds Bs OE ee ee SLE Hydrobius (Pl. Xd). .t23 eb a ae ee eee 51 HT. QlobOSUS sis 6 7 A See Oe Re ee 52 EL. fUSCUDES faces AA ORS DORR Le OE ee 55 HH, tesselatus. ck sie Be he OO ee 55 I. SCADTOSUS Sau ee 8 Sit es EL Ce 55 FH ClOCOMDUS .. Mica sce Ate Ries a ee rao Cymbiodyta (Blu) ee oe ee er ae il ree 56 Cs fam britany ee eC ea 57 CC DLaN Chandi ecco AS OEE Helochares (Rl: SED) 3.28 Stans da eee 61 EL. maculicoults ea sad eee ee Ae EO eee 62 EE normattisn fi 28s ee Le ee eee 65 ‘ Philydrus' (Pl. XIV)o. 0 ee 65 3 Piper plewus sacs o& Salie alah eo tee ee eg ae ee ee 67 PND UlOSUS ois be ee aces vac ee aceon 69 IP OCRTOCEUS 3. Aoi eo OS ee 70 DP CUNCEUS ciel fb sic Le ESO Oe 70 Pe NAMitltonrecs oss tte eels ie Bee Se Eee 70 Ancona: (PV eV ies sco ee ee ev he ee eee WA AL ANUS COED bch lsc) che aieotas cous eae SEDER L Paracymus (Pl. SEV) circ oes oe ee de Oe ae eee 74 Ps SUDCUPT CUS. sciatic Se tlee oo oe eae ee 9. “Spheeridinnse: :95. 220. sn 2a ss Se eee a DE RraT0O GENETIC! CONSUDE RATIONS se ae rs ae iene ee eee 77 I DNAse 6 rere ea PE APE He OU CPE ARS Rieger vn GEA Oe Ar eo Sag we 0 6 82 TRIB O=CASES soto Lia coy 8 cag toh cupecet Mytets hun Tec OU ed a 82 A DET hie sree ete ee eer een Fe nen aie wise pS Rh ae kl ue oe o big eo 0 ¢ 83 PUP ee ye. Soe Sess Soh is eas ita lO IGS Ra eae Se 87 Wetec O1G eo 29U MOT eN ee ee Me Sarees ne Ne i ae Une pee ene ete 88 $ I.—_INTRODUCTION In this country very little attention has been devoted to the biology of the water beetles of the family Hydrophilide, and there exists a woe- ful lack of knowledge concerning the immature stages. A general sur- vey of the aquatic members of the family was begun by the author in the spring of 1914 and has been continued until the present time. Primarily the New York State species, especially those occurring in the vicinity of Ithaca, have been dealt with but the collection of the United States National Museum (which consists mostly of European material) has also been examined. All the genera here discussed have been reared by the author. Some specimens of the genus Hydrous were furnished through the courtesy of Dr. Robert Matheson of Cornell University. Throughout this paper the classification as given by the European authors has been maintained as far as advisable, the grouping in use in this country not having been influenced by the recent work of foreign authors. For help toward the completion of this paper, I am greatly indebted to the following men: Dr. J. G. Needham, who personally directed this work; Mr. F. E. Wintersteiner, who so willingly helped in the identifica- tion of the adults; Dr. Adam Boving of the United States National Museum, who gave valuable suggestions in regard to the larve, descrip- tions and drawings; and Dr. L. O. Howard, who kindly placed the specimens of the United States National Museum at my disposal. A set of the material upon which this paper is based is deposited in The American Museum of Natural History. HISTORICAL The Hydrophilide as a distinct group was first recognized by Latreille! when, in 1804, he applied the name Spheridiota to this family. The earliest data found concerning the biology pertain to the genera Hydrous and Hydrophilus. This was presented respectively by Frisch in 1721 and Roesel in 1749. Until the middle of the nineteenth century very little was added; and it was not until Schiddte’s Monograph in 1861 that any collected work of note appeared. The little work that has been done in this country upon the natural history of this group of beetles consists only of scattered observations on the larger species. Life histories of American forms have been con- iLatreille, 1804, Hist. Nat. Crust. Ins., X, Ann. XII, p. 48. 3 4 Bulletin American Museum of Natural History [Vol. XLII tributed by Garman, Riley, and Matheson on Hydrous triangularis; by Wickham on Tropisternus glaber; by Wickham and Bowditch on Hydrocharis obtusatus; and by Béving on Hydroscapha natans. In Europe there has been more activity.. The work of Schiddte, 1861-1872, stands foremost and his results have been well supplemented by that of Balfour-Browne, Megusar, Miall, Planet, Duges, Reitter, Ganglbauer, and d’Orchymont. Schlick, Wesenberg-Lund, and Béving in Denmark have reared much important material, most of which has, through the efforts of Dr. Béving, been deposited in the National Museum at Washington. They have, however, published very little of their results. The most valuable papers of today are those of Ganglbauer and d’Orchymont. The former’s paper gives a lengthy survey of the family, based on the life histories as well as on adult structures. The latter’s work presents new life histories in a number of genera, careful descrip- tions and figures, a discussion of the larval breathing apparatus, and a generic key to the known larve. Balfour-Browne has given the most complete treatise on any one species. He treats the entire life history of Hydrobius fuscipes from egg to adult, describing each stage and its biology in full and accompanies the whole with excellent figures. It seems advisable to mention only the most important authors at this point. The others will be considered under the biology of the Separate genera. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 5 Table of known life histories of aquatic Hydrophilide (American genera) ry | | | CouNTRY NAME Eee | Larva | Pupa | INVESTIGATOR | Damp Helophorus | 1. aquaticus Linn. - = * Schiddte Denmark, 1862 2. granularis Linn. b3 = | * Schiddte Denmark, 1862 3. rufipes Bosc. : Perris France, | 1876 4. viridicollis Steph. | Incomplete |Zambeu France, | 1894 5. schmidti Villa ii Zambeu France, 1894 6. micans Fald. et Ganglbauer Austria, | 1904 7. lacustris Lec. z em Author United States, this pa per 8. sp. ? 2 zs Author United States, this paper Limnebius 1. truncatellus Noted but not/d’Orchymont __|France, Thumbg. a 3 dese. 1915 2. discolor Casey = a Author (descr. |United States, in part) this paper Ochthebius | 1. punctatus Steph. | Haliday England, | 1856 2. subinteger Muls.- | % | (Mulsant-Rey France, 1861 Rey, subsp. le-. { Fauvel France, 1865 jolisi Muls.-Rey \d’Orchymont France, 1913 3. quadricollis Muls. = | Ray France, 1887 4. impressus Marsh. Noted but not d’Orchymont France, desc. 1913 5. steinbuehleri Reitt ze | dOrchymont _|France, | 1913 6. tuberculatus Lec. # Z | ‘Author United States, | | this paper TES) Oats ‘i = | Author United States, | this paper 6 Bulletin American Museum of Natural History [Vol. XLII Table of known life histories of aquatic Hydrophilide (American genera) | | | CouUNTRY NAME Kee | Larva Pupa INVESTIGATOR | Dare Hydrena 1. pennsylvanica ed z Author [United States, Iiesw. this paper Hydroscapha 1. natians Lec. i iH * |Béving UnitedStates, 1914 Hydrochous | Lesquamifersweck 3) s i Author United States, this paper Hydrophilus || Roesel Germany, 1749 1. caraboides Linn. | * * # { Lyonnet France, 1832 | Denmark, | Schiddte 1862 2. obtusatus Say z i ‘Bowditch Mass., 1884 2 5: = /Wickham Iowa, 1895 - " cs /Author New York, this paper Tropisternus 1. lateralis Fabr. Y = Duges Mexico, 1884 2. glaber Herbst # Y Wickham United States, (Iowa), 1893 * a i Author United States, this paper Hydrous 1. piceus Linn. = = # Miger France, 1809 2. aterrimus Eschsch| * Schiddte Denmark, | 1862 3. triangularis Say 2 2 (Garman United States, 4 1881 ce zt s [Riley United States, 1881 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide a Table of known life histories of aquatic Hydrophilide (American genera) z | | CouNTRY NAME | Hae | Larva Pura | INVESTIGATOR Teese | Berosus | 1_ spinosus Stev. i - 3? Schiddte Denmark, : | 1862 2. signaticollis ihe + ( Schiddte ‘Denmark, Charp. | 4 1872 | | Brocher France, 1911 3. striatus Say os : Author United States, this paper 4. peregrinus Herbst} * | ‘Author United States, | | this paper Laccobius Psp: ? * d’Orehymont France, | 1913 2. agilis Randall y : = Author ) United States, | this paper Ancena 1. limbata Fabr. - | d’Orchymont France, | 1913 2. infuscata Motsch.| * | - Author UnitedStates, | this paper Paracymus | 1. eneus Germ. Incomplete Zambeu France, | 1894 2. subcupreus Say || - | z Author United States, | | this paper | Hydrobius | 1. fuscipes Linn. ae z ‘Cussae France, 1855 « “ Schiddte Denmark, | 1862 qi is Incomplete Balfour-Browne England,1910 2. globosus Say ciel 2 Author United states, | this paper Chetarthria 1. atra Le Conte Undescribed. Bulletin American Museum of Natural History [Vol. XLII Table of known life histories of aquatic Hydrophilide (American genera) ue | | | CountTRY NAME | Eac | Larva | PUPA INVESTIGATOR | Damp Helochares 1. lividus Forst. . * Incomplete | {Cussae France, 1852 { Schiddte Denmark, [ 1862 2. maculicollis Muls.; * = zt Author United States, | this paper Cymbiodyta 1. fimbriata Melsh. i = ‘ Author United States, this paper 2. blanchardi Horn z : ‘i Author United States, | this paper Helocombus 1. bifidus Lec. Undescribed. Philydrus 1. testaceus Fabr. i = zt Schiddte Denmark, 1862 Pag JAR DAEUS USO, | = ‘s Author United States, | this paper 3. nebulosus Say | i Y z Author UnitedStates, | this paper 4. ochraceus Melsh. : * Author United States, | this paper 5. cinctus Say APG | Author United States, | this paper 6. hamiltoni Horn ate Author UnitedStates, this paper METHODS OF COLLECTING The majority of these beetles live at the water’s edge and, if the soil, grass, or other vegetation is stirred rapidly 6r washed briskly with the water, the Hydrophilids will soon be released and come to the surface. They can then be easily gathered by the hand or, if small enough, by the forefinger. They do not become submerged immediately as do the 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 9 Dytiscidz but swim about on the surface until they regain shore or find some plant to aid them in descending. An examination of the banks adjacent to the collecting grounds at the time of transformation will offer good collecting because often the larval skin, pupal skin, and adult may be procured in the pupal cell at one time. Some of the species are attracted by are lights during warm nights and, in fact, it is there that Hydrous is most frequently obtained. Mertuops oF REARING The isolation, according to species, of adults, which readily lay eggs in captivity, proved the best method of acquainting oneself with the immature stages. Newly hatched larve are thus easily obtained. The most advisable temporary aquarium for such work seems to be a small stender dish. A small stone, half submerged in the water and draped with Cladophora gave excellent conditions for egg laying, especially for the smaller beetles which, as a rule, lay their eggs in moist places and not directly in the water. For larve, larger containers produce better results. Moreover, they should be arranged as aquaria-terraria, for many of the adults and larvee spend most of their time on shore. In preparing this, it is best to get some mud from the bottom or edge of a pool and, after placing it in the container to the depth of about an inch, slope it up gradually so that it forms a miniature bank. The bank end should be normally high enough so as to be a little dry on the surface. Cladophora and money- wort make the best plant materials because of their cleanness and last- ing qualities. Asa rule, the container should be filled so that the bank is covered and then placed in the sun. In a few days, the time depending on the conditions in the pool where the mud was obtained, numerous entomostracans destined to be food for the future larve will be present. The vegetation is then added. The larve, when fully grown, seem restless and try to crawl out. If the time for transforming has arrived, they rapidly burrow down and form their pupal cells. Some, however, pupate on the surface of the terrarium, evidently not liking the conditions below. Slightly moist earth seems to be the most natural substance for the terrartum and an inch or so depth will suffice. If not too deep, they will often make their cell next to the glass container, where it is favorable for observation. 10 Bulletin American Museum of Natural History [Vol. XLIT II—LIFE HISTORY AND BIOLOGY GENERAL SURVEY Without doubt, the water-scavengers are the most abundant of our water beetles. In this respect they are approached only by the Dytiscide which are better adapted to aquatic life. The smaller members of this group are very numerous, and yet are often overlooked. Their most common habitat is within the confines of some little pool which, as the seasons progress, becomes filled with algze and other aquatic vegetation. Nevertheless, all the species may be taken in rapidly flowing streams but usually near the bank in débris, moss, ete., or in protected bays, where the water flows the slowest. One isolated record shows the capture of Cymbiodyta fimbriata beneath some falls in a bed of moss. The genera which are best adapted for living at some depth and under harsher conditions than the others are Hydrous, Tropi- sternus and Berosus. The adult is chiefly herbivorous. It feeds mostly on the lower plant forms, such as alge, but does not seem to be restricted to this diet. Decaying vegetation is its most popular food and it feeds readily on dead animal tissue (earthworms, larve, ete.). It is an air breather, though much of its time is spent below the water. To obtain air! the beetle comes to the surface and extends its pubescent antennze above water. They are then folded under the head and the air which has gathered on the antennz is passed on to the hairs of the prothorax. Inspiration takes place by means of the pro-meso- thoracic spiracles only. The air passes through the trachez and, as fast as used, is expelled through the other seven pairs of spiracles. It then spreads over the ventral side of the abdomen, where it is held as a film by the hydroscopic hairs. Thus the characteristic air film is formed. When a fresh supply is needed, the used air is passed along the prothorax to the antennz again and the process repeated. Continual contraction and expansion of the body accompanies this breathing process. Most of the Hydrophilide hibernate as imagines. It would be hard to tell where all of them spend their winter but a number of the species have been found in the bank a few feet from the water. They do not burrow down very deeply but remain near the surface, apparently in readiness to enter the water during any warm spell. An examination of the beetles which were taken from the bank or in early spring often 1Brocher in his excellent paper (1913) carefully explains the respiration of Hydrophilus. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide i! showed their bodies to be covered with many mites. Species of Podophrya and of Epistylus were also quite frequently observed upon them. Their lack of activity evidently allowed these harmless epizoans to gather on them; after a few days in the aquarium, they were lost. The principal egg-laying months are May and August, although the egg-cases of some species may. be found during the entire summer. The eggs, usually placed in ‘‘cocoons”’ (better called egg-cases) of silken structure, hatch out in about seven days. Many eggs are laid by a single individual, thus making up part of the enormous mortality which occurs among the young larve.’ The silken material which protects the eggs is secreted by the female from glands located in the caudal end of the body. It is applied by the two spinnerets in a manner very much resembling the way a paint brush is used. A continuous flow of silk is laid down at each turn. According to Miger. there are in Hydrous three secretions, each of which has a different use. The first for loose spinning is used for covering the individual egg; the second for constructing the egg-case; and the third to form the mast at its tip. The function of this mast is a problem, although many suggest that it aerates the case. Several genera place their cases or single eggs below water, so that this supposition does not appear entirely plausible. The larve, when first appearing, are whitish in color, except for the reddish pigment of the ocular areas, but soon the chitinized portions of the body darken. The first duty of the aquatic larve is evidently to get what is called an “air drink.” They lift their heads above water and, with the aid of a pharyngeal pump, draw air into their alimentary canal. Air is also taken into the trachee through the stigmatic atrium which rests upon the surface film. By thus supplying their bodies with air the larve become buoyant. Otherwise they would be heavier than water and soon sink, dying because of lack of oxygen. The larve are carnivorous and cannibalistic as well, the different genera varying in their greed. The young larve feed upon small organ- isms (entomostracans,! Tubifex, leeches, etc.) and increase the size of their prey as they themselves increase in size. The full-grown larva feeds readily on pollywogs, annelids, fish, and, in fact, almost anything that it can overcome or that is fed to it. It lies In wait for its prey with its jaws extended widely and, as a rule, is half in the water and half out, the caudal end being out. When it begins 1 Helo phorus was observed feeding on Simocephalus, Cypris, Cypridopsis, Cyclops, ana Canthocampus. 12 Bulletin American Museum of Natural History [Vol. XLII eating, the larva lifts its head out of the water and manipulates its food by means of the mouth-parts. The labium and maxille are used as guides and to hold the prey while the mandibles macerate it. The legs play no part in the handling of the food. Predigestion occurs and the dissolved food is then drawn into the mouth by the suction of the pharynx.! There is neither lock to the mouth nor tubes in the mandibles such as are found in the dytiscid larva. This method of feeding refers only to the aquatic larvee of the family and to Helophorus. I have not observed the feeding of the other, terrestrial forms. According to d’Orchymont, however, predigestion apparently does not take place in them. There are usually two molts occurring during the larval period, which lasts one or two months. Hydrobius” evidently proves an excep- tion to the rule, as its larve are found nearly full-grown in the early spring and even then do not transform immediately. The typically aquatic larva grows very rapidly and the first two instars take only about a fortnight. Most of its life is, therefore, spent in the third or last instar. When ready to pupate, the larve leave the water and burrow in moist earth, often under stones or sticks, where they mold a cell shghtly larger than the pupa to be formed. In the prescribed time (8-7 days) the pupal skin is ruptured and the adult emerges soon after but usually remains in the cell until fully colored. EXPLANATION OF TERMS USED In order that the terms that are used in the technical descriptions may be understood by the reader, a brief explanation of them is given here and illustrations of typical structures are shown in Plate I. No work has yet appeared in this country which deals with the difficult structures of a campodeiform larva such as we find in this family. Hopkins’ paper on Dendroctonus has proved very useful, but the struc- tures of that type of larva have not been compared with those of the hydrophilid type. I have, therefore, used, for the most part, the terms employed by European writers. D’Orchymont does not discuss the various terminologies, except in regard to the stigmatic atrium. How- ever, his labeled figures of the mouth-parts and his numerous notes aid materially in giving one a clear understanding of his interpretation of 1Method described by Balfour-Browne, 1910. 2Miall reports hibernation in larve of H. fuscipes and the author has observed it in H. globosus. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 13 the various structures. Dr. Béving, who has studied the attachment of muscles in larve, has kindly offered valuable suggestions as to the homol- ogies of the abdominal folds. The fully developed and typical hydrophilid egg-case consists of the egg-case proper, containing the eggs; a cap covering the entrance to the latter and a projection continuous with the cap, which may be either a horny mast, tube, or filament. In giving the measurements of the case, the cap has always been considered as one end of the case. The head of the larva may be inclined, horizontal, or elevated, with respect to the axis of the body, depending upon the shortening or lengthening of its upper or lower side. The epicranial suture, which may be present or absent, is formed by the union of the frontal sutures along the median line. The gula is the sclerite to which the submentum is attached. The epistoma is the sclerite just behind the clypeus and its lateral expansions attain the front margin of the head just lateral to the labro-clypeus. Schiddte called their angular projection the frontal angle. The upper surface of the mouth region on the under side of the labrum is the epipharynx; and, on the under surface, continuous with the mentum, is the hypopharynx. Ocular area is the term used for each of the eye spots behind the antenne because ocellus is misleading and must be restricted to the adult. The antennal appendage is a finger- like lobe borne by the second segment of the antenna, and there may be two of these appendages. The lacina mobilis mandibult is a flat unjointed lobe which the posterior piece of the mandible bears; it is toothed apically. The molar surface of the mandible is the grinding inner sur- face near its base. The parts of the labium and maxilla may be seen in Plate I, figs. 1 and 5. Palpifer is restricted to the palpus-bearing seg- ment of the maxilla, while palpiger is applied to that segment of the labium. “Articulating piece of maxilla” refers to the area between the eardo and the labium upon which the maxilla articulates. A segment of the larva consists of a tergum, two pleura, and a sternum. The folds of the abdomen are very confusing and need further study. I have considered the hypothetical types of the abdominal tergum as possessing four transverse areas, namely, the preescutum, two scuta and a scutellum. The prescutal area is flat, while the other areas are represented by transverse folds. Between adjacent segments of the abdomen, there is a prominent region which is called the “intersegmental membrane.” This may possibly be the postscutellum, but it has not been considered as such in this paper. The number of folds in this area is two at the most 14 Bulletin American Museum of Natural History [Vol. XLII The spiracular area, which bears the spiracle, is just lateral to the tergum. The pleural region is composed of the hypopleurite and the epi- pleurite, the latter above the former. They are usually fairly distinct and bear lobes. The sternal region usually consists of the same number of folds as the tergal region but is much more complex. As in the latter, there are corresponding folds known as the presternum, sterna (two folds) and sternellum. The stigmatic atrium, or caudal breathing apparatus, offers oppor- tunity for controversy as to the segments which compose it, but I have considered it as formed by the modified eighth and ninth segments. The procercus is the process of the eighth pleurite; the mesocercus, or true cercus, is always an appendage of the ninth segment; the acrocercus is an appendage of the lateral lobe of the ninth segment and arises from its ventral side; and the prostyle (‘‘flotteurs”’ of Portier), which pre- cedes the anus, is an appendage of the tenth segment. The motory stylus is a fleshy process of the pupa, resembling a seta. It may or may not bear a terminal seta and is usually annulate. The pterotheca is the pupal covering of the adult wing. GENERAL CHARACTERS OF THE FAMILY (IMMATURE STAGES) The eggs are whitish (brownish in Hydroscapha), oval in shape, and with a small projection at the anterior end. The eggs, varying in number from one to one hundred and forty odd, are usually enclosed in a silken case! but, in the more primitive forms (Ochthebius, Limnebius, and Hydroscapha), the eggs are deposited singly, without any covering or with one of loosely applied silk. Cymbiodyta and Paracymus lay their eggs in masses but cover them only sparsely with silk. The cases are either free floating (Hydrous, Hydrophilus); attached to water plants or débris at the surface of the water (Tropisternus, Philydrus, Hydrobius, Laccobius, Ancena); below water (Berosus); embedded in mud, moss, etc. (Hydrobius, Helophorus); carried on the under side of the body (Spercheus, Epimetopus, Helochares, Chetarthria ?); or placed in dung or damp earth. The egg-masses of Cymbiodyta and Paracymus and the single eggs of the more primitive species are deposited under fallen leaves, vegetation or stones near the edge of the water. 1Stein, 1847, who found silk glands in many genera, supposed that all ezgs were covered with silk but the degree of covering varies greatly. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 15 The larva is campodeiform; its head inclined (more primitive genera), elevated (more specialized genera), or nearly horizontal (Helo- phorus, Hydrochous); ocular areas in groups of five or six, distant or aggregated, reddish, round or oval, convex or flattened; antenne three- segmented, rarely four-segmented (full-grown larva of Hydrous triangu- laris); epicranial suture present or absent; points of insertion of an- tennz situated nearer or farther from the externo-frontal angles than those of the mandibles; labrum and elypeus well developed and distinct (more primitive genera) or reduced and fused (more specialized genera) ; mandibles with lacinia mobilis or sharply pointed and with inner teeth; maxilla palpiform or with stipes possessing a well-developed inner lobe; maxillary palpi three-segmented; labial palpi two-segmented; ligula present or absent; gula well developed and attaining the occipital opening or reduced and not attaining the occipital opening; labium and maxillze inserted in a furrow on the under side of the head (more primitive genera) or not inserted in a furrow (more specialized genera) ; legs segmented and with claw-like tarsi, without tarsi (Spheridium), or legs entirely absent (Cercyon). Abdomen with nine well-developed segments and a reduced tenth or eight well-developed segments and reduced ninth and tenth. The body is usually slightly chitinized. The types of breathing overlap but there is a marked tendency in each genus towards one of three types: holopneustic, apneustic, or metapneustic. The spiracles (one pair of mesothoracic and eight pairs of abdominal) may be well developed bifore spiracles (Helophorus), annuliform spiracles (Ochthebius, Limnebius, Hydrena), apparently absent (Hydroscapha), or poorly developed bifore spiracles (the remaining genera). Cerci absent (Hydroscapha) or present as three-segmented or two-segmented appendages; reduced in the higher forms. The pupa is usually white in color except the eyes, which are red- dish at first but change to nearly black before emergence. However, Tropisternus lateralis and Hydrophilus obtusatus are greenish. The anterior and posterior ends of the body are incurved and are not visible from the dorsalside. The integument is smooth, except that it is sparsely covered with styli. The supraorbital sete are usually present but there is only one in Hydrous triangularis and none in Tropisternus glaber. The pronotal styli vary in number and size. There are only sixteen in 1The pupa of the most primitive forms has not been descriked. 16 Bulletin American Museum of Natural History (Vol. XLIT Helophorus and thirty-two in Hydrophilus. The number seems to be constant in the Hydrobiine as all specimens examined had twenty-four styl. Both the meso- and metathorax have a dorsal transverse row of two setze. The wings are folded down over the ventral side of the body and the metathoracic pterothecz may (terrestrial species) or may not (others) be visible from above. The first to seventh abdominal seg- ments each possess, dorsally, a transverse row of four to six styl. The second to seventh abdominal pleurites each bear a stylus. The cerci are present and well developed. GENERAL CHARACTERS, LirE History, AND BIOLOGY OF THE ForMS STUDIED 1. Helophorine Egg-case proper continuous with a distinctly hollow tube at the cap end. Many eggs enclosed. Larva with the head nearly horizontal, slightly elevated; ocular areas round, convex, and in groups of six, closely aggregated; antenne with their points of insertion nearer the externo-frontal angles than those of the mandibles; antennal appendages of second segment two in number; epicranial suture absent; labrum and eclypeus reduced; mandibles stout, sharply pointed, and with distinct inner teeth; labium and maxilla inserted at the anterior margin of the under side of the head; maxilla palpiform; palpiger slightly dichotomous at the distal end; gula reduced and distant from the occipital opening. Abdomen with nine complete seg- ments, each with tuberclar areas, the tenth distinct but reduced; cerci three-seg- mented Holopneustic type of breathing with well-developed bifore spiracles. HetLopHorvus Fabricius Often taken in company with the common Ancena and Paracymus, these three genera are the most abundant in the Cayuga Lake basin. All representatives of this genus may inhabit the same pool but more frequently the different species seem to be segregated. It is difficult to distinguish the various species in the field but, as a rule, H. lacustris may be known by its usually larger size. In addition to it, H. linearis, H. viridicollis (lineatus), and H. granularis, named in the order of their abundance, are found here. Very little work has been done in this country on the species. They are very close to each other in structure. Distribution is limited, the representatives occurring only in the pale- arctic, nearctic, and Central American regions. European authors have worked extensively on the life histories of Helophorus and they are listed in the table (page 5), but in America nothing has been done. However, H. granularis, which Schiddte described, is holarctic. Egg-cases were taken out-doors in May and June. The cases were formed in moss or alga near the bank with only the tubular filament exposed, the egg-case proper being hidden completely. From six to ten eggs were found in each of the cases. During the latter part of May sev- eral larve were taken, in company with Ancena larve, from the under side of a stick at the water’s edge. While the larve have been observed eating entomostracans and various other animal tissue, it is worth re- calling Perris’ note that H. rugosus was observed in the stalk of Brassica preying on a Psylliodes larva. 17 18 Bulletin American Museum of Natural History [Vol. XLII Helophorus lacustris LeConte Plate II Two egg-cases were noted deeply embedded in moss at the water- line and only the tubes were visible. The cases proper were covered with sand and mud but the tubular filaments were clean and white. Thirteen larvee were obtained from these cases and they made their escape through the tubes. A preserved case shows three of the larve in the tube at one time, one behind another. Several other cases were obtained in the laboratory, where they were laid in some alga which had been pulled out of the water and placed on the side of the aquarium. A part of the alga was left hanging in the water and this kept the re- mainder moist. Eaa-case! somewhat flask-shaped. Egg-case proper nearly round, measuring 1.69 mm. in width; tube, 0.94 mm. wide distally. The whole 4.84 mm. long; the opening is obliquely across the end of the tube and extends 1.076 mm. down the side. Newty Hatcuep Larva.—Length, 2.55 mm.; width, 0.403 mm. Whitish except chitinized portions, which are brownish with head yellowish in part; integu- ment more chitinous than in other larvee and with only a few scattered sete. Head quadrangular, only slightly elevated, dorsal side one-half the ventral in length, posterior margin with a prominent semicircular emargination; fronto- clypeal suture weakly indicated, more prominent towards the middle; frontal sutures converging gradually and joined by a short transverse suture contiguous with the posterior margin of the head; epicranial suture absent; gula poryeonal; gular sutures confluent; cervical sclerites evidently not present. Labro-clypeus triangular (subconical). Lateral expansion of the epistoma prominent, similar, rounded, about even with the anterior margin of the labro- clypeus and each bearing seven, stout, recurved spines; epipharynx spinous. Ocular areas in groups of six and closely aggregated; roundish; arranged in two rows of three each and all equidistant from each other. The hind row set slightly nearer the median line than the front row. Antenne short, slightly exceeding the mandibles; first segment about as long as the second, slightly constricted near the base; second segment widened towards the tip, obliquely truncate, possessing distally in the membrane a pair of two-segmented, lobiform antennal appendages on the outer side in addition to a strong seta and two strong distal setze on the inner side; terminal segment cylindrical, much narrower than the other segments and provided with several apical sete. Mandibles symmetrical, prominent, sharply pointed at their tips and with the inner surface of the anterior piece serrate; two” inner teeth on each mandible about equal in size; a strong medio-lateral spine present; molar areas smooth, 1The egg-case of H. aquaticus figured by Schiddte differs greatly from our generic type and I doubt his accuracy. 2H. granularis has only a single inner tooth. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 19 Mawnillze with palpifer not joint-like; stipes fairly large, swollen, not notice- ably narrowed towards the apex, only a little longer than the palpifer, its inner surface provided with a row of five stout setz, another just inside the most distal one and two slender set near the externo-distal angle; palpifer fairly large, a little longer than wide, bearing an inner stout lateral seta; a slender seta in the externo- distal angle and a slender cylindrical appendage in the interno-distal angle, exceeding the first segment of the palpus, with sense-cones and a seta at its tip as well as those nears its base; palpus cylindrical, tapering slightly with sense-cones at the distal end; the second segment slightly longer than the other two. Labium not exceeding the mandibles, but prominent and just attaining the distal end of the palpifer; submentum small; mentum not exceeding the tooth of the labro- elypeus, cylindrical, a little longer than wide, and slightly swollen distally; palpiger equal to the mentum in length, its sides diverging and forked distally; the palpi, borne by the two forks, cylindrical and tapering; the second segment about twice as long as the first and with sense-cones at the tip; ligula absent. Prothorax with angles obtuse; well indicated, only a little wider than the head, sides parallel; anterior and posterior of pronotum non-chitinized; sagittal line present; prosternum chitinized in front and lateral to the cox. Mesothorax and metathorax equal to each other in Jength but shorter than the prothorax and becoming very slightly narrower than the latter caudally. The nota are entirely chitinized and each bears a transverse row of four prominent sete. The sagittal line, which continues throughout the eighth abdominal segment, prominent. A pair of bifore spiracles on the mesothorax. Legs fairly long, slightly longer than the thorax is wide; coxe transverse, grooved laterally to receive the femora; femora a little longer than the tibiew; tarsi claw-like, about as long as the latter and with no inner sete; the anterior cox are closer together than the four posterior coxze, which are about the same distance apart. Abdomen with nine distinct segments, very slightly narrowed caudally. Anal segment projecting, short and cylindrical; the first seven abdominal tergites similar and resemble the meso- and metanota in the arrangement of the sets and their chitinization. Dorsally a row of four setz on each segment, each seta emerging from a broad, rough tubercled area, which is chitinized and separated from the others by a longitudinal furrow or suture. Laterally two similar chitinized tubercled areas, the posterior one larger and with a seta (both probably correspond with the epipleurite) ; hypopleurite similar, one-lobed and with a seta. The sagittal suture very distinct as well as the longitudinal furrows. Ninth segment narrower than the eighth and nearly twice as long with a prominent lateral seta on each side, corresponding to the seta of the lateral tubercled areas just mentioned; only the tergite is chitinized. Arising from the posterior margin are two divergent, three-segmented, cylindrical, tapering cerci. The first segment bears a ventral and dorsal seta, the second a terminal seta just below the origin of the third segment, which has a terminal seta as long as the three segments together. The three segments bear the relation of 16, 12, and 18 to each other in length. Each spiracle! is just below and in front of the outer dorsal tubercled area. First eight sternites with a transverse row of four tubercles, each bearing a seta which has a small, chitinous plate at its base, and a small seta each side of the median line near the anterior margin. Three transverse folds are present iCompared with the other Hydrophilidz, which possess them,the bifore spiracles are well developed. 20 Bulletin American Museum of Natural History [Vol. XLII ventrally, the first ovo-oblong, the second somewhat rectangular, and the third tri- partite with the middle bilobed, each lobe with a seta, the lateral parts triangular and with a seta. Helophorus aquaticus Linnzeus The identical life history material of this European species used by Schiddte in his work on this genus is located in the collection of the United States National Museum but is in poor condition. An examina- tion of the full-grown larva shows that the sclerites in front of the pro- coxee are not so prominent as in the younger larve. The abdomen is only slightly more strongly chitinized than in the first stage larva and the intersegmental membranes are present but not prominent. The setze are lost in the specimen examined but this may be due to its poor condition. The following pupal description may well be incorporated. Poupa.—Length, 8.5 mm.; width, 2.00 mm. at its thorax. Whitish (specimea browned with age). Head smooth and bears two supraorbital styli on each side. Pronotum smocth, its anterior margin somewhat vrilobed and its posterior margin with a large median lobe. The styli! are arranged as follows: ten on the lateral and anterior margins, two of which are on the middle Icbe; six on the posterior margin, counting the two corner ones; no styli are to be seen in the central area of the pro- notum but may have been destreved. (Schiddte’s figure gives none.) Mesonotum and metanotum with a transverse row of two sete. Inner spur of metatibia fairly prominent. All tarsi probably ending in a spine but not very clear and tibie not noticeably spinous on the outer side. Metathoracie pterothece conspicuous from above. First to seventh abdominal tergites with a transverse row of four styli. Second to seventh pleurites each with a stylus, all arising from small conical tubercles; eighth tergite somewhat semicircular, the rounded posterior border bearing two styli; one lateral stylus noted on each side below the eighth tergite; ninth segment with a pair of short, conical, feshy cerci about the same length as the ninth tergite. They diverge only slightly and their sharp tips point inwardly. 2. Limnebiine Ayes laid singly with a slight covering of loosely applied silk. Larva with head inclined; antenne with points of insertion situated nearer the externo-frontal angles than those of the mandibles; epicranial suture present; ocular areas round, couvex and in groups of five, aot closely aggregated; labrum and clypeus both well developed; mandibles each with a lacinia mobilis; maxilla primitive with an inner lobe; labium with short palpi; fleshy lizula present; labium and maxille inserted in a furrow on the under side of the head; gula well developed and attaining the occipital opening. Nine complete abdominal segments each with a ventral and dorsal plate, and a distinct but reduced tenth or anal segment. Cerci two-segmented. Holopneustic type with annuliform spiracles. 1The basal part of the stylus is short and the terminal seta long. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 21 LIMNEBIUS Leach -D’Orchymont gave the first description of the larva of Limnebius. The eggs and pupa have not been described. Limnebius discolor Casey Three specimens were taken the latter part of June near the bank ~ of an alga-filled pool. The species is rare and has not been previously reported from Cayuga Lake basin. It is difficult to recognize in the field on account of its small size, but closer examination shows clearly its resemblance to the Hydrobine type, with which it was formerly classed. The eggs were laid on July 1 by captured specimens and one egg hatched on July 8. As this was the only larva obtained, it is considered inadvisable to give a description of it. However, the larva very closely resembles L. truncatellus, which d’Orchymont carefully described. cS) 5). Hydrenine Eggs laid singly. In Ochthebius with or without a slight covering of loosely applied silk but in Hydrena covered with a blanket of closely span silk. Larva as with Limnebiine. OcuTHEBIUS Leach Ochthebius offers many interesting structures. O. tuberculatus is particularly unique and cannot be mistaken for any of the other species. Besides O. tuberculatus, O. holmbergi and several other undetermined members occur in the Cayuga Lake basin. All of them are,in general, quite rare. However, when once located, many are usually collected in a very small area and one collecting ground kept me well supplied from late April until winter set in. The soil in this spot was especially sandy. Upon washing the sand with water and pulling up and washing the roots of the vegetation which grew there, many specimens were soon observed floating on the surface of the water or clinging to floating débris. Haliday, 1855-6, was the first to figure a larva of this genus, namely, O. punctatus. The latest and best study is that of d’Orchymont. He worked out in detail the larva of O. lejolisi, already described by Mulsant and Rey, 1861, and worked over by Fauvel, 1865. D’Orchymont also dealt with steinbuhleri and impressus. Rey, 1887, added O. quadri- collis to the list of known larve. bo bo Bulletin American Museum of Natural History [Vol. XLII Single eggs were deposited on the stones or algze in an aquarium, out of water but in moist places. They were either entirely naked or, at times, covered rather uniformly with loosely applied silk. The silk was more compact, however, than in the scattered silk of the Cym- biodyta egg-masses but not as closely applied as in the complete egg-cases. The eggs were most frequent during May but some were laid the first part of July. From seven to ten days were required for incubation. The larve are very different from those of the Hydrobiine and even from those of the Helophorine but are closely allied to the Limnebine. On land, they move very rapidly and almost seem to run. They are very clumsy in water and doubtless spend their life on land but in moist situations. According to d’Orchymont, p. 190, the life of the larva probably lasts only two or three months. Adults of O. impressus, which he captured the first of August in order to restock his aquaria, were not fully colored, thereby indicating their recent emergence. Ochthebius tuberculatus LeConte (foveicollis LeConte) Plate III At times the collecting of this species proved so easy that they could be picked up almost indefinitely, the collector stopping only to wash them out. In the middle of September 1916 many were found in eravelly places which were practically devoid of vegetation. One can easily recognize them in the water because of their somewhat heart- shaped abdomen, which often sinks lower than the rest of the body. Eeea.—Length, 0.538 mm.; width, 0.215 mm. Naked or covered with loosely applied silk which is placed regularly so that the whole is unifcrm in shape. Newxy Hatrcuep Larva.—Length, 1.345 mm.; width, 0.242 mm. Whitish, except the chitinized portions which soon become brown. Integument with many inconspicuous setulze as well as regularly arranged sets, which are fairly long, rigid, and brownish. Head well rounded, globular; fronto-clypeal suture fairly well indicated; frontal sutures converging, uniting behind the middle of the head to form the epicranial suture, the whole presenting a Y-shaped appearance; frons somewhat trianguiar. Gula fairly small, constricted laterally, the anterior and posterior angles produced into arms; cervical sclerites, if present, not noticeable. Epistoma apparently marke off from the frons by an irregular group of minute tubercles. Clypeus fairly distinct, transverse, slightly arched, wider than the labrum and with a transverse row of six sete, the median two widely separated but the others equidistant, near the anterior margin. Labrum somewhat semicircular with four lateral sete on each side, the anterior one bifurcate, short, and blunt; a stout seta in front of the latter; two, small, adjacent tubercles just inside the anterior margin and two others in a horizontal row 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 23 through middle but widely separated; two sete just posterior and outside the former tubercles and two others posterior but inside the latter tubercles, both in a horizontal row. The lateral expansions of the epistoma not prominent. Epipharynx apparently not spinous. Ocular areas round, five on each side, not aggregated; the first and second not seen from above, fairly close together and placed one back of the other just behind the insertion of the mandible at the side; the third and fourth about the same distance apart as the first two and located just posterior to the insertion of the antenna, the fourth more dorsal and posterior; the fifth widely separated from the fourth, more lateral and posterior. Antenne three-segmented,! fairly long, exceeding the mandibles; first segment more than twice as wide as long and less than one-third the second segment in length; latter about the same width, slightly constricted in the middle and with an outer swelling just proximal to the middle, bearing a small, blunt spine; distal end with four long setze; third segment slightly constricted and distally with several prominent sete. Mandibles approximately symmetrical with broad bases, their tips with several finger-like processes, the arrangement on two mandibles differmg somewhat; lacinia mobilis present, pectinate distally; molar area with numerous spinules and two inner teeth in front of it. Maxillz with palpifer jomt-lke and seeming to form the first segment of the palpus; a large internal lobe present, which clasps the stipes on the ventral side and shows a tendency to be divided distally into two lobes; the outer lobe tapers to a sharp point while the inner lobe is shorter, blunter, and fringed with a row of stout setz distally as well as with several slender sete nearer its base; cardo noticeable and as broad as the stipes at its union; stipes wider and longer than the palpifer and with two lateral sete; palpifer about as wide as long; palpus tapering; second seg- ment slender and only slightly longer than the first; terminal segment very small and somewhat flask-shaped. Labium with palpi barely exceeding the labrum, short; submentum, reduced, transverse, indistinct; mentum broad but longer than wide, slightly constricted; palpiger transverse, slightly forked; palpus short, two-segmented, articulating membranes well developed; second segment narrower, shorter than the first, its margin flared distally and with apical sete and papille; ligula present, barely ex- ceeding the first segment of the palpus, rounded and furnished with papille (very similar to Limnebius). Prothorax with sides and angles rounded, of the same width as the head. Pro- scutum well developed and entirely chitinized, sagittal line present; anterior and posterior margins with a transverse row of sete; a median transverse row of sete and several lateral sete. Mesothorax a little shorter than the latter, slightly narrowed in front. Meso- scutum well developed and entirely chitinized, less conspicuously in front; sagittal line present; a transverse row of sets just in front of the middle and at the posterior margin; several lateral sete. Metathorax the same. Sterna not noticeably chitinized. Legs fairly long, about as long as the thorax is wide; coxe transverse with a - dorsal groove; femora about the same length as the tibiz but a little stouter; tarsi slightly more than one-third the latter, claw-like and with no inner set. 1Articulating membrane at base very prominent but non-chitinized. 24 Bulletin American Museum of Natural History [Vol. XLII Abdomen with ten distinct segments and narrowed caudally. The first eight tergites similar and each covered by a dorsal plate, the posterior angles and margin of which are rounded; a transverse row of sete at the posterior margin and a fairly prominent seta at each side. Hight pairs of small round spiracles present and each situated in the spiracular area just inside and anterior of the lateral sete. Pleural groove distinct. Each segment with a ventral plate less chitinized towards the anterior and with sete arranged as on the dorsal plate. Ninth segment similar to the preceding ones, except that it is slightly longer and the irregular row of sete are absent at the posterior margin, inside the insertion of the cerci. A pair of two-seg- mented, divergent cerci arise from the posterior margin of the ninth tergite, their points of insertion almost contiguous. First segment of cercus, longer than the anal or tenth segment, chitinized, constricted slightly in the middle and with several long distal setze besides other shorter ones; second segment slender but not tapering; less than one-half the first segment in length and bearing a single, long, terminal seta. Anal segment cylindrical, longer than wide, banded with chitin, the tip membra- nous, a row of short setze around the caudal border of the band and a terminal pair of stout, recurved hooks directed downward. Hyprana Kugel Only one species, H. pennsylvanica, is found in the vicinity of Cayuga Lake. One cannot fail to recognize the members of this genus because of their long, slender maxillary palpi and almost invariably hexagonal pronotum. Hydrena pennsylvanica Kieswetter Plate IV The life history of this minute water scavenger has never been described. The small, elongate beetles are often overlooked unless one collects especially for them. They are found either in flowing or stand- ing water and occur most frequently where the shore is muddy or gravelly. Specimens were collected throughout the spring and summer at the same special collecting grounds but they proved to be most numerous in April and May. Once located, the same spot will yield specimens for the rest of the season. The stock pool for 1915 was one of the railroad pools, east of the tracks of the Lehigh Valley Railroad, Auburn Division, and south of Fall Creek, where on April 14 over forty were taken by washing out the mud at the shore-line. During late August many of the beetles were observed crawling over stones and pebbles where the water lapped the shore of Cayuga Lake near the mouth of Taughannock Creek. Their most common associates are Paracymus subcupreus, Ochthebius tuberculatus, Hydrochous squamifer, and Cercyon ocellatus. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 29 As with Ochthebius, only one egg is deposited at a time. Eggs were laid in an aquarium during the middle and latter part of April. They were placed on a leaf which rested on a stone, some in the water and some out but always in a damp situation. Each egg was kept in position by a blanket-like covering of closely applied silk which exceeded the egg on all sides and showed its form. The eggs hatch in six to eight days, emerging through a narrow, longitudinal sht in the upper side of the egg-case. The larve are very rapid walkers and closely resemble those of Ochthebius, almost seeming to glide over the surface of the stones when stimulated. They are clearly non-aquatic in their movements, becoming quite helpless when below the surface film. Eae.—Length, 0.591 mm.; width, 0.242 mm. The flare-like margin exceeds the egg itself about 0.09415 mm. all around and is entire, being only slightly irregular. Newry Hatcuep Larva.—Length, 1.29 mm.; width, 0.242 mm. Whitish except chitinized regions which soon become brown; integument with many incon- spicuous setulz as well as regularly arranged sete which are fairly long, stiff and brownish. Head strongly rounded, globular; fronto-clypeal suture weakly indicated, except at the sides; frontal sutures, converging, unite behind the middle of the head to form the epicranial suture, the whole presenting a Y-shaped appearance; gula small, constricted laterally, and its posterior angles extend to form long, lateral arms; cervical sclerites, if present, not noticeable. Clypeus fairly distinct, transverse, slightly arched, wider than the labrum and with a transverse row of six equidistant setz on the posterior half. Labrum somewhat semicircular with four sete on each side, the anterior one prominently branched (almost pectinate) while the third pair are strongly bent in- ward and tapering; anterior margin slightly emarginate with a short, finger-like appendage on each side, with a seta just behind but a little lateral; four other sets on the upper side of the labrum; two near the middle and two on the posterior half but more widely separated. The lateral expansions of the epistoma are not prominent. Epipharynx apparently not spinous. Ocular areas round, five on.each side, not aggregated; the first and second close together and placed one above the other just behind the gena? and below the base of the antenna; the third and fourth closely approximated, widely separated from the latter, and more dorsal; the fifth near the lateral margin of the head and distant from the fifth. Antenne fairly long, barely exceeding the mandibles; first segment about as wide as long and two-fifths the second segment in length; latter more slender with two swellings on the inner side, one at the middle, bearing a long seta and one near the distal end bearing a finger-like appendage besides a long seta; two seta just below the externo-frontal angle; third segment slender, longer than the finger-like appen- dage and more than one-half as long as the second with a seta arising from an inner tubercle near the middle and several terminal setze mounted on tubercles. iMany adults were taken in copulo out of doors at this season. *The scierite called the gena may open some question but it evidently corresponds in position to it. 26 Bulletin American Museum of Natural History [Vol. XLII Mandibles approximately symmetrical with broad bases, their tips with several finger-like processes; lacinia mobilis broad and toothed distally; two small inner teeth; molar area oval with its surface covered with numerous spinules and four small teeth in front of them. Maxille with palpifer joint-like and seeming to form the first segment of the palpus; a large terminal lobe present, which clasps the stipes on the ventral side and is divided distally into two lobes fringed with setze; the inner lobe with a row of sete on its inner margin; stipes slightly wider and longer than the palpifer, which bears four inner sete; palpus tapering and with the second segment slender and longer than the first; terminal segment very small and somewhat flask-shaped. Labium with palpi barely exceeding the labrum, short; submentum reduced, transverse; mentum broad, cordiform; palpiger transverse, indistinct; palpus short, coverging, distally provided with sete and expanded with a flare-like margin; articu- lating membranes well developed; ligula slightly exceeding the first segment of the palpus, bowl-shaped and with large rounded papille at its tip. Prothorax with sides and angles rounded, of the same width as the head. Pro- scutum well developed and entirely chitinized; sagittal line present; anterior and posterior margins with a transverse row of sete; a median transverse row of seta and a prominent lateral seta on each side near the middle. Mesothorax slightly narrower but the same length as the prothorax. Mesoscutum well developed and entirely chitinized; sagittal line present; the posterior margin with a transverse row of sete, a transverse row on its anterior half and a medio-lateral seta on each side. The metathorax the same except that it isa little narrower. Sterna not noticeably chitinized. Legs long, about one-half longer than the thorax is wide; coxe transverse with a slight dorsal groove; femora a little shorter than the tibize; tarsi claw-like, more than one-fourth the latter in length, with no inner sete but each with two incon- spicuous outer ones. Abdomen with ten distinct segments and narrowed caudally. The first eight tergites similar and each covered by a dorsal plate,! the anterior margin of which is straight while the posterior is rounded; a transverse row of six sete at each posterior margin and a prominent lateral seta on each side arising from a small tubercle. Spiracles situated just inside and anterior of the lateral seta. Pleural groove distinct. Wach segment with a ventral plate! less chitinized anteriorly and possessing a trans- verse row of six setze near the posterior margin besides several others just anterior. Ninth segment similar to the preceding ones except that it is slightly longer, four inner dorsal setze are lost, both lateral sete are more posterior, and the median pair of ventral setz at the posterior margin are set a little more anterior. A pair of two- segmented, divergent cerci arise from the posterior margin of the tergite, their points of insertion distant from each other. First segment of cercus tapering, longer than the anal or tenth segment, chitinized, and bearimg two dorsal setz near its base, three sete about one-third the length of the segment from the distal end,? and a terminal ventral one. Second segment small, slender, cylindrical, only slightly chitinized, its tip flattened, membranous and bearing a terminal seta. 1The dorsal piate represents the scutum fused with the epimerites while the ventral plate represents the sternites fused with the episternites (d’Orchymont). 2The first segment appears to be subdivided but closer examination disproves it. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide Pah Anal segment cylindrical, longer than wide, and banded with chitin, the tip membranous, a transverse row of sets anterior of the caudal border of the band and a terminal pair of stout, recurved hooks directed downward. 4. Hydroscaphine Eggs jaid singly without a covering of silk. Larva with inelined head; antennze with points of insertion situated nearer the externo-frontal angles than those of the mandibles; epicranial sutures present; ocular areas round, convex and in groups of five more closely aggregated than with the other primitive larvze: labrum well developed but clypeus! not present; mandibles small each with a lacinia mobilis and concealed from above by the labrum; maxilla primitive with an inner lobe; labium with short palpi; labium and maxille inserted in a furrow on the under side of the head; gula well developed and attaining the occipital opening. Nine complete abdominal segments, and a distinct but reduced tenth segment, the chitinized portion of all ten forming a continuous ring. Tracheal gills present on several segments. Spiracles reduced so that the openings cannot be seen. Cerci absent. .. Hydrochoine Egg-case flat with a single egg enclosed. Larva with head inclined, antennze with their points of insertion situated nearer the externo-frontal angles than those of the mandibles are; epicranial suture absent; ocular areas oval and in groups of six, closely aggregated; labro-clypeus very much reduced, the epistoma apparently at the anterior margin of the head; mandibles prominent, each with a slender distal piece terminating in a stout seta; and with a lacinia mobilis; maxilla palpiform, the inner side of the stipes with a small swelling; palpifer without a rudimentary lobe; labium with short palpi and ligula absent; labium and maxille inserted in a furrow on the under side of the head; gula small but attains the occipital opening; eight complete abdominal segments, and each with a dorsal and ventral plate. Ninth and tenth segments reduced. Type of breathing pseudo-metapneustic and the bifore spiracles are poorly developed. Hydrochous Leach As with the genus Helophorus, we find most of the species very closely related. However, the rare Hydrochous scabratus, with its promi- nently tubercled elytra, is a well-marked species. The most common species is H. squamifer but two closely allied and undetermined species (possibly undescribed) are almost as abundant. A few specimens of _H. excavatus ? have also been recorded. The only genus with which the collector might confuse the adult is Helophorus but the former is easily differentiated in the water by the angular form and blackish color, which has a decided tendency to be iridescent. The seven- segmented antenne and discal foveee of Hydrochous clearly separate it from Helophorus with its nine-segmented antenne and discal sulci. 1The clypeus may have fused with the labrum. 28 Bulletin American Museum of Natural History [Vol. XLII In gathering the species, one finds them most frequently in company with Ochthebius, Hydrena, Helophorus, Ancena and Paracymus but a great deal harder to locate, with the possible exception of the two first named. They seem to cling more tightly to the vegetation at the shore- line with their rather powerful claws. Standmg water with gravelly bottoms and little vegetation or muddy pools seem to be their most common habitat. About fifty were taken the latter part of August 1916 in a lagoon west of the Cornell Biological Field Station. The waters at that time of the year are filled with Ceratophyllum (hornwort), Spirodela (duckweed), and Elodea, while cat-tails abound, taking root in the muddy bottom. Hydrochous was procured at the water’s edge by washing the mud away from the roots of the cat-tails. They came to the surface immediately and, although very slow in action, they would quickly become submerged by grasping the vegetation with their claws unless washed out in deeper water. When their station, which seems to change each year, is once located they may be captured in large numbers but, otherwise, only scattered specimens are usually taken. - A single specimen of H. scabratus was procured in Dwyer’s Pond by sweeping the submerged Elodea. When the imagos were placed in the aquarium they immediately sought the under sides of some stones, below the water, but when it was placed in the sun they soon came up, seeking the sunny side. A few days later they were observed eating holes in decaying leaves of moneywort and Marsilea, leaving only the tough veins. The life history has not been described and it has proven to be of particular value in explaining the phylogeny of the family. Although the larva has a well-developed stigmatic atrium, yet its head and mouth- parts are quite primitive. The laying season seems to be confined to the beginning of summer weather, about the latter part of May and the first of June. From the fifty imagos taken the latter part of August, not a single egg-case was obtained. A number of the beetles were taken in copuloon May 10 but no cases appeared until about May 23. A single egg was deposited at a time and placed between two layers of closely applied silk. The cases were fastened down to the alge or rocks in the aquarium, either above or below water, and held firmly by the flap and stanchions. One case of - Hydrochous sp.? was particularly well supplied with little stanchions. The egg-case of this genus is apparently one step forward from the egg- case of Hydrena in specialization. The larvee appeared through a rupture in the silk in about seven to eight days. They were quite at home in the water and the manner in 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 29 which the lobes and cerci, around the terminal spiracles, spread out over the surface of the water showed clearly its advanced development. They are much less active out of water than the Hydreenine but never- theless move rapid. Hydrochous squamifer LeConte Plate V EaaG-case.—Length of egg, 0.6 mm.; width, 0.2 mm. The case is irregular in outline and varies in size but the egg is always placed towards one end of the case, the two layers of silk meeting to form a flap at the other end. Newty Hatcuep Larva.—Length, 1.8-1.9mm.; width at the thorax, 0.21-0.24 mm. Whitish except chitinized regions which soon darken; integument with many inconspicuous setule. Body somewhat cylindrical. Head strongly rounded, shorter than wide, nearly horizontal; fronto-clypeal suture not visible; frontal sutures converging as far back as the middle of the head but then slightly diverging and not uniting to form the epicranial suture, the frons therefore concave at the sides; gula small, its posterior angles extended to form long lateral arms; cervical sclerites, if present, not noticeable. Labro-clypeus very much reduced, the epistoma apparently at the anterior margin of the head, nearly straight in front, no toothed lobe present but with a trans- verse row of eight setz at the anterior margin arranged in two groups of four equi- distant from the median line; area immediately behind the latter bearing numerous setz mounted on minute tubercles. Lateral expansions of the epistoma not promi- nent, rounded, and similar. Epipharynx with sete on small tubercles; ocular areas in groups of six, oval, closely aggregated, arranged somewhat in a circle (the third and fourth slightly distant) with their longitudinal axes emanating from the center. Antenne fairly short, reaching only to the middle of the palpifer; first segment stout, slightly concave on the inside and slightly convex on the outside, about one- third longer than wide; second segment less than one-third the latter in length, narrower, a little longer than wire and bearing distally a finger-like antennal appen- dage in addition to the third segment; the latter not quite as long as the second seg- ment and about as long as the appendage but alittle wider and bearing terminal sense- cones. The intersegmental membranes separating the segments are well developed and allow the last two segments to be telescoped. Mandibles symmetrical, the anterior pieces fairly slender, only slightly tapering, the tips membranous and each bearing a short recurved seta; lacinia mobilis slender and bifid at the tip; a single, sharply pointed inner tooth just in front of the molar area; latter setiferous. Maxillz with palpifer joint-like, stipes large, sides parallel, the inside with a prominent swelling surmounted by a group of sete; palpifer shorter but equal in width, about as long as wide, swollen, three prominent inner sete in addition to many small setze mounted on minute tubercles, which cover the inside of the stipes as well; palpus tapering slightly, the second segment longer than the first but shorter than the thimble-like terminal segment which possesses apical sense-cones. 30 Bulletin American Museum of Natural History [Vol. XLII Labium barely exceeding the stipes of the maxilla, union of submentum and mentum not clear but submentum probably small while mentum is longer and cordi- form; palpiger about as long as wide, cylindrical; palpus short; the first segment about one-half the second, which has small distal sete that are mounted on minute tubercles. Ligula absent. Prothorax with sides rounded, of the same width as the head; entirely chitinized; sagittal line present throughout the thorax. Meso- and metathorax similar, of the same width but a little shorter than the prothorax. Legs not quite as long as the thorax is wide and robust; coxe oval, transverse and with a dorsal groove; femora, tibiz, and tarsi all about the same length; tarsi well developed, basal part iong, claw-like and bearing two inner sete. Abdomen with eight distinct segments, all of the same width, ninth and tenth rudimentary. The first seven tergites similar and intersegmental membrane not well defined. Each segment covered with a dorsal plate, the anterior margin of which is straight while the posterior is rounded; no prominent setze present but a lateral inconspicuous seta. Bifore spiracles mounted on small tubercles, just inside and anterior to the lateral seta. Pleural groove distinct. Each segment apparently with a ventral plate corresponding in structure with the dorsal plate; eighth segment with sides only slightly rounded out, of the same width as the preceding one. It represents - the superior valve of the stigmatic atrium and its caudal border is four-lobed, each lobe bearing a seta. Procercus, or process of the eighth pleurite, one-segmented with a terminal seta. Mesocereus (cercus) two-segmented, tapering, the first elongate dome-shaped, the second about the same length but more slender and with a terminal seta and covered with several small tubercles, each with an apical seta. Ninth tergite divided into three lobes, two lateral and one median; median lobe! small and a little longer than wide with its caudal margin nearly straight and bearing a short but prominent seta at each caudo-lateral angle; outer or lateral lobes large, rounded and with a terminal seta; acrocercus below and its distal end shows between the lateral lobe and the median lobe just mentioned. 6. Sphercheine* Egg-case carried by the hind legs and held on the under side of the body. Larva with head slightly inclined; ocular areas round and in groups of five, not closely aggregated; antennee with points of insertion nearer the externo-frontal angles than those of the mandibles; epicranial suture very short, almost absent; labro-clypeus very much reduced, the epistoma apparently limiting the front margin of the head; mandibles stout, sharply pointed, furrowed internally and with mner teeth; maxilla palpiform but with palpifer bearing an inner lobe or lacinia; labium with palpi and ligula short; labium and maxille inserted in a furrow on the under sid? of the head; gula well developed and attaining the occipital opening. Eight complete abdominal segments, the ninth and tenth reduced. The type of breathing is pseudo- metapneustic and with poorly developed bifore spiracles. Seven pairs of short conical gills on the first seven segments. Cerci and prostyles present but reduced. 1This median lobe seems to articulate at its base and may be the remains of the tenth segment of the lower Hydrophilide. . 2This subfamily is not represented in this country but is incorporated on account of its unique specialization. 1920} Richmond, Studies on the Biology of the Aquatic Hydrophilide Bill 7. Hydrophiline Egg-cases characterized by their horny mast and comparatively larger size. Larva with elevated head; antennz with points of insertion farther from the externo-frontal angles than those of the mandibles; second segment without an antennal appendage; epicranial suture absent or very short; ocular area flat, elongate and closely aggre- gated although distinctly separated; both labrum and clypeus almost entirely reduced, the front margin nearly straight and with only a few small teeth. Mandibles prominent, sharply pointed, furrowed internally and with inner teeth; maxilla palpiform, slender, the stipes longer than the palpifer and palpus together, palpiger with an inner rudimentary lobe; labium with palpus longer than in the primitive genera, the second segment distinctly longer than the first; ligula present, labrum and maxillz inserted at the anterior margin of the under side of the head; gula reduced and not attaining the occipital opening. Legs provided with fringe of sete. Eight complete, non-chitinized abdominal segments; ninth and tenth reduced. Type of breathing pseudo-metapneustic and with poorly developed bifore spiracles. Tracheal gills, if present, not well developed. Cerci reduced but two-segmented. Prostyles present or absent. HypropuHitus Leach There are fewer species in this genus than there are in Hydrous, but the members of Hydrophilus are more equally distributed over the world. One of the four American representatives, H. obtusatus, occurs at Ithaca. The well-known European species, H. caraboides, was one of Lin- nus’ species and Roesel in 1749 knew some of its larval instars besides the pupa. lLyonet was the first to describe the egg-case and Schiddte later gave the entire life history. The egg-case and young larva of H. obtusatus were figured by Bowditch in 1884. He gave a very interesting aecount of its biology but did not observe the pupa. The full-grown larva and pupa were later described by Wickham but the figures are of little value and the descriptions meagre. Although it varies in size, it 1s our second largest hydrophilid and is intermediate, in this respect, between Tropisternus and Hydrous. The beetle is very clumsy and in no way approaches the two other genera of this subfamily in aquatic adaptation. It is most frequently found in leaf-filled pools, mud holes, at the water’s edge under débris or clumps of grass, or in pools overgrown with vegeta- tion. Several adults are often taken together in such situations, but only isolated specimens are usually recorded. Hydrophilus obtusatus Say Plate I, Figures 1, 2, and 6; Plate VI The egg-cases of H. obtusatus appear in late May and early June but are not often reported. The fact that they are usually covered with a 32 Bulletin American Museum of Natural History [Vol. XLIT dead leaf makes it more difficult to see them. They float freely and are the most picturesque of all the egg-cases. A case was formed indoors on April 22 and, as there were no leaves present in the aquarium, it was placed in a mass of floating algze. No definite air chamber such as is found in Hydrous is present. The eggs, about forty in number, are laid in a vertical position at the bottom of the case. Just behind the cap is a mass of loosely spun silk. The cap end is never covered by the leaf but the larve do not always emerge underneath it, as seems to be the rule in Hydrous. More often the escape is made at the other end. The young larve fed readily on Cyclops, Cypridopsis, etc., and made several attempts to catch small tadpoles. Freshly killed tadpoles were placed within their reach but they evidently did not care for the dead food. According to Bowditch, they become full grown in about thirty days and spend the remainder of the summer and winter as pupe, emerging early in the spring. Such an extraordinary length in the pupal stage may be true but it does not sound plausible nor is it always the case. In July a mature larva was captured floating in the middle of a lagoon near the Biological Field Station. It was placed in a terrarium and on July 21 started burrowing down. After several attemps to form a suitable cell below the surface, it finally pupated above ground July 28. The process of transformation took less than an hour and a beautiful sea-green pupa resulted. Five days later the adult emerged. At the time of emergence the beetle was piceous above but its under side was light brownish in color. Eaa-case.—Whitish except brownish mast and plate at its base. Case without the leaf 9.2 mm.—18 mm. long, 9.8 mm.—11 mm. wide, and 7.8 mm.—9 mm. high. The horn-like mast, arising vertically from the top of the largest or cap end of the case, is from 7mm.—11.8mm.in length. It is enlarged at the base into a roundish plate about 4—4.5mm. high. Thetop of the mast is often bent forward and away from the ease. Newry Harcuep Larvya.—tLength, 6.5-7 mm.; width at the thorax, 1.25 mm. Light brownish in color. Integument entirely pilose. Head broadly ovate, constricted behind, elevated; fronto-clypeal suture well indicated at the sides; frontal sutures gradually converging but not uniting until they attain the caudal margin of the head; frons raised in the middle; gula reduced, arched, semicircular, and with the gular sutures prominent and confluent. Cervical sclerites present. Labro-clypeus nearly symmetrical, reduced, with very small inconspicuous teeth at the anterior margin and a row of five small setze equidistant from each other. Lateral expansions of epistoma similar and broadly rounded, overlapping the bases small short sete along their margins. Ocular areas in groups of six arranged in two parallel rows, the first three nearly vertically, while the posterior three are horizontally placed. The sixth area or outer one of the posterior row distant from the fifth. Articulating maxillary piece fairly well developed. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 373) Antenne slender, extending forward about as far as the tips of the mandibles; first segment much longer than the second and third together, slightly constricted near the base, a little crooked and with a few short conical spines on its inner surface; second segment bent inwardly a little, slightly longer than the terminal segment and with a disto-medial seta; latter segment more slender and possessing a few distal setze. Mandibles symmetrical,’ prominent, elongate, sharply pointed at their tips and with their inner surfaces grooved; each mandible with two inner teeth, the proximal tooth smaller than the distal and shghtly bifid; distal tooth furrowed on its inner surface, and the furrow is continuous with a furrow surrounding the proximal tooth. Maxillee slender and with joint-lixe palpifer; stipes swollen near its base, slightly bowed, longer than the palpifer and palpus together and its inner surface with a row oi five sete, the basal four fairly stout; palpifer with a small chitmous appendage bearing a terminal seta at its disto-medial angle; about twice the length of the Ist palpal segment but only very slightly wider; palpal segments all about the same width and bearimg the relation of 7, 13, and 20; terminal segment with a single distal sense-cone. Labium prominent, palpus nearly attaining the distal end of the stipes, its first segment short, the second the same width but about five times as long and with terminal sense-cones; ligula well developed, more than twice as long as the first palpal segment, cylindrical, only slightly tapering, chitinized except tip; palpiger four- elevenths longer than wide, sides parallel; mentum cordiform, anterior angles pro- nounced and acute; submentum extremely transverse, small and joint-like. Prothorax narrower than the head, sides parallel; pronotum bearing a few scattered setze; entirely chitinized except at the anterior margin and the sagittal line, which continues through the thorax; a large ventral sclerite present in front of the prothoracic coxe. Meso- and metathorax similar to each other, a little wider than but less than one-half as long as the prothorax, each with a pair of fairly large, irregular subtri- angular sclerites and a lateral tubercle. A bifore spiracle present in each antero- lateral angle of the mesothorax while, corresponding in position to it, there is a small tubercle on the metathorax. Pro-mesothoracic and meso-metathoracie sclerites are present and are small, elongate, horizontal plates. Legs about twice as long as the width of the thorax; segments beginning with coxe bear the relation of 35, 12, 35, 25 and 15; tarsi well developed, claw-like, and each with two inner sete, one dorsal to the other. Abdomen with eight distinct segments, narrowed posteriorly, ninth and tenth rudimentary. The first seven tergites similar, each with two very much reduced, oval, chitinized patches on the proscutum, the first pair larger than the others, and four small but conspicuous tubercles in a transverse row across the posterior or second fold of the scutum, each bearing a seta. Each tergite consists of three transverse folds while the intersegmental membrane has only one; sternites with similar arrange- ment except that there is a longitudinal fold on each side of the three transverse folds. Seven pairs of rudimentary bifore spiracles and seven pairs of pleural appendages, equally long (0.48 mm.), on the first seven segments. A small dorsal tubercle at the base of the appendage. The eighth tergite represents the superior valve of the stig- = H. glacus the mandibles are asymmetrical. The left mandible possesses only a single inner tooth. 34 Bulletin American Museum of Natural History [Vol. XLII matic atrium and bears a large, chitinized plate, somewhat dome-shaped anteriorly. Caudal margin of the eighth tergite is slightly quadrilobed, each lobe with an un- chitinized tip and several distal sete. Procercus well developed, its first segment prominent, with a chitinous band partly surrounding it and a distal tubercle as well as a small terminal segment, bear- ing an apical seta. Mesocercus fairly prominent, chitinized, two-segmented, each segment with an apical seta. The chitinous plate in front of the mesocerci distinct and with two transverse rows of sete arranged in pairs; the posterior row with one pair and the anterior row with three pairs; median lobe of ninth tergite rounded and with a ventral chitinized plate which tends to wrap around it. Acrocercus situated below each lateral lobe of the ninth tergite, and with two terminal tubercles, each bearing a seta. FuLi-Grown Larva.—Length, 25-27 mm.; width at the thorax, 5mm. General color is brownish above and dirty white below. The chitinized regions are castaneous. When about ready to pupate, it takes on a greenish gray coloration, probably due to the color pigment of the pupa. The head measures 3.25 mm in width and 1.99 mm. along the mid-dorsal] line. First segment of antenna slightly longer than in first stage, about one-fifth the second. Labro-clypeus inconspicuously crenate. Mandibles stouter, blunter and with the proximal inner tooth not noticeably bifid. Lobe of palpifer very rudimentary; dorsal surface of mentum with scattered setz and four lateral spines which are more prominent; ligula very slightly divided at distal end. Seta in the caudal angle of the mesoscutum prominent. Prostyles or anal append- ages not noticeably longer (1.2 mm.). Pupa.—Length, 15 mm. with cerci (curled up); width at the thorax, 8 mm. Sea-greenish except whitish tubercles, styli, cerci and tip of abdomen. Whitish parts become brown as emergence time approaches and metathoracic wings fuscous. Head smooth; two supraorbital styli present; two small oval raised areas on each side of the epicranial suture near the vertex. Pronotum smooth, its cephalic margin concave. Styli arranged as follows: three equally long styli,! curving back- wards, in a transverse row at the anterior margin at each side; a group of three others similarly arranged but decreasing in length towards the middle, just inside the latter; three in a longitudinal row at each lateral margin; a transverse row of ten at the posterior margin (more slender and less recurved than latter); two transverse rows near the middle; the anterior row with four styli, the posterior with three. Meso- and metanotum with a pair of styli in a transverse row. Metathoracic pterothecee visible from above. Tarsi not ending in prominent spines nor tibize spinous on the outer side. A transverse row of six motory styli on the first seven abdominal tergites, the outer one on each side mounted on a tubercle. Second to seventh pleurites each with a stylus or a tubercle. Eighth tergite with two small, rounded tubercles at the posterior margin on each side of the median line and each bearing a short terminal stylus. Ninth segment terminating in two, superficially annulate cerci, which are 2.85 mm. long, divergent, tapering and bifid at their tips. Spiracles raised and prominent. 1These pronotal styli on the front margin and middle region have no terminal seta. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 35 TROPISTERNUS Solier Although the adults appear to be closely allied to Hydrous, the differ- ences found in the immature stages tend to strengthen the validity of this genus. The adults differ from Hydrous principally in their smaller size and in the structure of the maxillary palpi. They are the most common members of the Hydrophiline and may be taken in almost any pool or lagoon. Although more active than most of the water scavengers the adults are easily captured by hand. T. glaber, T. mixtus, and T. lateralis are the representatives in thisregion. The former two strongly resemble each other but 7. lateralis can easily be distinguished on account of the narrow yellow margin of the prothorax and elytra. T. glaber is by far the most abundant species. The genus is limited to America in its distribution. Duges, 1884, was the first to give the characters of the immature stages. His descriptions of the larva and pupa of 7. lateralis, collected in Mexico, were carefully done but his figures are not very helpful. Wickham, 1893, added the larva and pupa of 7. glaber. The egg-case has apparently been unmentioned in literature. This seems strange as "the cases, at least those of 7’. glaber, are very common at the commence- ment of the warm summer days. Tropisternus glaber Herbst Plate VII The egg-cases cannot be mistaken; the horny mast is peculiar to the subfamily to which this genus belongs; the case is not as long as the naked case of Hydrous and is not wrapped up in a leaf as is the case of Hydrophilus. Instead, it is fastened to a leaf, blade of grass, or any kind of vegetation present at the surface of the water. The cap covers one end of the case and the mast is firmly attached to it. There are from eleven to twenty-two eggs contained within and the time of incubation is six to seven days. The main dates of develop- ment of an individual observed in 1914 were as follows: May 25, egg deposited in the case; May 30, larva emerged; July 1, burrowed; July 10, pupated; July 14, adult emerged. The young larve were placed in an aquarium where they fed readily on entomostracans and small tadpoles. The different molts were not observed. Only a few larve reached maturity, as the weaker individuals were quickly eaten by the stronger ones. During the latter part of June and the first few weeks in July many full-grown larve were taken out-of- 36 Bulletin American Museum of Natural History [Vol. XLII doors at the edge of the pools under stones, débris, or even some distance from the shore on the surface of the alga-filled pools. The larve are found all summer but this first generation of the year is the most abun- dant. The second generation begins soon after the adults emerge, the greatest number of egg-cases of this generation being found the first part of August. Pupz were secured about the same time of the year within their cells an inch below the surface of the bank or under stones. When transforming indoors, many of the pupee did not form a cell below ground but changed at the surface. The cells formed were about 12 mm. wide, 10 mm. high and nearly round. The earth in the terraria was only about three-quarters of an inch deep so that the larva could be observed forming the cells next to the glass. The constant squirming of the larvee made the cell walls firm. The legs, especially the fore legs, helped materi- ally in shedding the pupal skin. The tarsi are bent back and the tibiz used in pushing the skin off. Upon emerging, the head of the beetle, the middle of the pronotum (the edges lighter), the scutellum, and the legs were brownish in color. The elytra were yellowish white and the abdomen whitish. It colored’ very rapidly and in about ten hours was entirely black above but shghtly brownish below. Ea@a-casp.—Whitish, except brownish mast. The measurements of case, which is figured, were 9.3 mm. long; 4.28 mm. wide at the cap end; 5.3 mm. wide at the other end; and the mast 4.8 mm. long. Newry Hatcuep Larva.—tLength, 4.8 mm.; width at the thorax, 0.84 mm. Light brownish (fulvous). Entire integument covered with fine short hairs. Head ovate; fronto-clypeal suture well mdicated at the sides; frontal sutures eradually converging and uniting to form a very short epicranial suture; frons raised in the middle, nearly triangular and with a transverse impressed line near its basal third; gula reduced, arched and semicircular but flattened posteriorly; gula sutures prominent and confluent. Cervical sclerites present. Labro-clypeus nearly symmetrical, reduced, with very small teeth, usually five, in the middle and one on each side of the latter five but removed a little; a transverse row of six setze just inside the margin. Lateral expansions of epistoma similar, rounded but somewhat straight in front, only barely exceeding the labro-clypeus with a row of inconspicuous setz on the inner side and overlapping the bases of the mandibles. Ocular areas in groups of six and arranged in parallel rows, the first three nearly vertically while the posterior three are horizontally placed. The sixth or outer one of the posterior row is distant from the fifth and in some specimens is rudimentary. Antenne extending forward about as far as the tips of the mandibles and beyond the first segment of the maxillary palpus; first segment ionger than the following two segments taken together but stouter than in the other Hydrophilinz; second segment slightly more slender and with several short sete in the membrane preceding the third 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 37 segment; latter still more slender, a little stouter than the second and with several distal setze in addition to a small, two-segmented, finger-like appendage.* Mandibles asymmetrical, prominent, elongate, sharply pointed at their tips, each mandible with two? inner toothed areas; the distal inner tooth on each well developed, bifid, their anterior margin minutely serrate, and their inner surface with a groove, which extends to the base of the mandibles; this latter groove sep- arates the proximal inner tooth of each mandible into two, equal, flat teeth; those on the left mandible are much larger than those on the right and with a curved edge, which crosses the groove, slightly proximal to them. Maxie with joint-like palpifer; cardo* small; stipes slender, swollen at the base, slightly constricted in the middle, longer than the palpifer and palpus together and its Inner surface with a row of five setze; palpifer only slightly narrower than stipes but less than one-fourth its Jength; a chitinous finger-like appendage at its interno- distal angle bearing a long seta and a microscopic lobe or sense-cone apically; palpus tapering and curving in slightly; the first segment small; the second about as long as the palpifer; the third a little longer than the latter and with terminal sense-cones. Labium prominent, the palpus nearly attaining the distal end of the stipes, its first segment short, the second of the same width but much longer and with terminal sense-cones and setie; ligula well developed, more than twice as long as the first palpal segment, cylindrical, only slightly tapering; palpiger a little longer than wide, slightly swollen; mentum subcordiform, anterior angles pronounced and sharply pointed; dorsal surface with numerous minute spines at its basal half; submentum extremely transverse and joint-like. Prothorax nearly as wide as the head, angles slightly rounded; pronotum entirely chitinized except at the anterior and posterior margin and possessing a few scattered setz besides a transverse row of six sete in front and a transverse row of four in back; a large ventral sclerite present in front of the prothoracic legs. Sagittal line continuous throughout the thorax. Pro-mesotergal sclerites are present and are small, elongate and horizontal. Mesothorax much shorter than the prothorax, about the same width and with a pair of fairly large, irregular, sclerites, each with a prominent seta caudally. Spira- cular area with three small tubercles. A rudimentary bifore spiracle present in each externo-frontal angle. Metathorax similar but slightly narrower and shorter and its sclerites more irregular caudally. A small pleural appendage present. Legs more than twice as long as the width of the thorax; segments beginning with coxz bear the relation of 16, 7, 16, 12, and 9; tarsi well developed, claw-like and each with two inner sete, one proximal to the other and smaller. Abdomen with eight distinct segments narrowed posteriorly, ninth and tenth rudimentary. The first seven tergites similar, each with two very much reduced, oval, chitinized patches on the preseutum, the first pair larger than the others, and four small but conspicuous tubercles in a transverse row across the posterior fold of the scutum, each bearing a long, colorless seta. Each tergite consists of three trans- tWickham, 1893, considers this appendage as one-segmented but remarks that it appears to be two-segmented. *Duges, 1883, describes T. lateralis as possessing only one inner tooth. The terminal segment of the maxillary palpus i is also small and cone-shaped. Wickham, 1893, said that he could not find the basal segment in his specimen although Duges had apparently observ ed it in 7. lateralis. 38 Bulletin American Museum of Natural History [Vol. XLII verse folds while the intersegmental membrane has only one; sternites with similar arrangement except that there is a longitudinal fold on each side of the three trans- verse folds and a fourth indistinct transverse fold was observed in some specimens. The bifore spiracles at the tip of small tubercles. Both the epipleurite and hypo- pleurite bear a tubercle. The transverse row of tubercles is lacking on the second fold of the sternite but a single prominent tubercle is present on each side of the third fold as well as one behind the middle of the longitudinal fold. The. eighth tergite represents the superior valve of the stigmatic atrium and bears a large, shield-shaped, chitinous plate, which is slightly emarginate at the middle of its anterior border but more prominently so just behind the two middle lobes of the caudal margin of the eighth tergite. The structure of the atrium is very close to that of Hydrophilus. It differs from the latter principally by the fact that the two middle lobes of the hind margin of the superior valve are more distinct resembling the mesocerci and that the two anterior sete of the plate in front of the cerci are set farther apart. The median lobe of the ninth tergite with two distal sete. The prostyles are short, not exceeding the sides of the body, broad, rounded, and depressed. FuLL-GROWN Larva.—Length, 14 mm.; width at the thorax, 3.2mm. General color brownish above and dirty white below; chitinized regions reddish brown. Head dorsally with a yellow stripe on each side; ventrally with a median and two lateral pairs of yellow stripes; measures 2 mm. in width and 1.44 mm. along the mid-dorsal line. First segment of antenna longer in proportion than in the first instar, more than four times the second segment. Labro-clypeus nearly straight, often slightly crenate, and some specimens retain the most lateral tooth of the first instar on each side, but it is very inconspicuous. Mandibles with the outer spur of bifid inner tooth lacking. Lobe of palpifer very much reduced; dorsal sete of mentum (about four- teen) arranged somewhat in a transverse elipse; externo-frontal angles rounded but prominent and with a small outer seta; tubercles of abdomen prominent and each bearing a group of long, slender, terminal sete. Pupa.—Length, 12 mm. (curled up); width at its thorax, 5.6 mm. Entirely whitish except reddish brown eyes.! Head smooth, no supraorbital sete, oval, raised areas on each side of the epicranical suture near the vertex very small. Pronotum smooth with middle lobes not prominent. Motory styli are long, fleshy and annulate, each bearing a terminal seta, slightly recurved and arranged as follows: three in a transverse row on each side near the anterior margin; four in the middle just back of the anterior margin, the two inner ones set back a little; six in a transverse row at the posterior margin (no corner styli); two on the basal half of each side; and two in a transverse row across the middle. Meso- and metanotum with a pair of transverse styli; scutellum well marked; metasternal spine long. Inner spur of metatibia very prominent. Tarsi not ending in prominent spines nor tibiz spinous on the outer side. Metathoracic pterotheca visible from above. First to seventh tergites with a transverse row of four styli, second to seventh pleurites each with a stylus. Eighth tergite with two very small indistinct lobes at its posterior margin on each side of the median line and each bearing small stylus. Ninth segment terminating in two crooked, fleshy, superficially annulate cerci aboug 1.45 mm. long. Cerci diverge as far as their 1A fresh pupa showed the eyes entirely white except the six pigment-spots of the ocular areas, which were grouped at hind margin of the head. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 39 middle and then converge. They are slightly bifid and sharply pomted. On the outer side of the distal third are two small spines. Abdominal spiracles (second to sixth) large, uncovered and the area about them well chitinized. Tropisternus sublevis LeConte A specimen of this species was examined at the National Museum. It is very close to 7. glaber. The proximal inner teeth of both mandibles are more reduced and the basal ridge of left mandible is lacking. Hydrous Leach The above generic name will doubtless be confusing to many be- cause our representatives have for so long a period been known under the genus Hydrophilus. Here are included the largest beetles of the family and, in Ithaca, only one species is to be found, namely, H. triangularis. This is well known to collectors and because of its large size, measuring over thirty millimeters in length, can not be mistaken. Its specific name is evidently due to the triangular spots of yellowish brown hair on the abdominal sternites. Adults have been collected during the warm spring and summer months under electric lights, toward which they often fly in large num- bers. One specimen was captured as late as November 1 under an are - light. The most rapid swimmers of the family are included in this genus. It is clearly seen that their bodies are well adapted for gliding through the water with the least possible resistance. European authors have paid a great deal of attention to H. ater- rimus and H. piceus, especially the latter, not only to their life history but also to their biology in its various phases. The earliest mention of the larval and pupal stages was made by Frisch as far back as 1721 but his unique error of describing the larva upside down and there- fore ascribing dorsal legs to it takes away part of its value. Miger and Lyonet follow about a century later and both papers are worthy of com- mendation. The life history of H. aterrimus given by Schiddte is pre- sented in the usual careful way of the author. The most complete work on the only American species considered is that of Dr. Robert Matheson of Cornell University, published in 1914. He has very carefully followed the entire life history of H. triangularis through all its stages from the egg to adult. Garman’s paper in 1881 on the egg-case and larva was well written but did not include the entire life history. It was supplemented by Riley’s paper in the same year. 40 Bulletin American Museum of Natural History [Vol. XLII Hydrous triangularis Say Plate I, Figure 7; Plate VIII . It hardly seems necessary to go into the biology of this species. However, the main events occur as follows. The egg-cases are found mostly in June, and, although always attached to floating leaves or other débris, have never been reported as fastened to living plants. Over one hundred eggs are enclosed within it and the larvee when newly hatched are very ungainly as compared with the full-grown larva. The usual two molts take place and the pupa appears in about one month. The duration of this latter stage is about eleven days. Eec-case.—Light brownish with its mast and plate at base of mast almost black. It measures 24mm. long, 15 mm. high, and about 22 mm. wide. The horn-like process, which arises from the cap end of the case, is almost at right angles with the upper side of the case and is usually 7-8 mm. long. Below the plate is a lunar-shaped opening which leads into a chamber below the eggs. Newriy Hatcuep Larva.—Length, 8 mm.; width at the thorax, 1.7 mm. Light brownish with appendages whitish darkening with age. Integument with fine dark hairs. Head, without mouth-parts, 1.14 mm. long dorsally and 1.82 mm. long ventrally; 2.1 mm. in width; broadly ovate, large, depressed, strongly elevated; fronto-clypeal suture well marked; frontal sutures widely separated, converging only slightly and not uniting to form an epicranial suture; gula fairly prominent, arched, semicircular behind; gular sutures confluent and distinct. Labro-clypeus reduced, with its anterior margin slightly concave and bearing a few microscopic projections towards each side. Lateral expansions of the epistoma similar, acute, not prominent. Ocular areas in groups of six, elongate and arranged in two parallel rows, the first three nearly vertically while the posterior three are horizontally placed. The sixth or outer one of the posterior row distant from the fifth. Antenne three-segmented, exceeding the right mandible by almost the length of the terminal segment, and left by its last and half of its penultimate segment; first segment longer than the second and third together, almost as long as the stipes, bent inwardly near the base and fringed on the inside, except the basal third, with slender sets; second segment swollen distally and not quite as long as the third, which bears no distinct terminal sense-cones. Mandibles asymmetrical, prominent, sharply pointed at their tips and with their inner surfaces grooved; each mandible with a single inner tooth, the inner tooth of the right mandible with a large tooth on its anterior margin forming an unequally bifid tooth; the left mandible stouter and shorter than the right and with a membra- nous area in the region of the molar surface. Maxillze with joint-like palpifer; stines slender, slightly bowed, longer than the palpifer and palpus together and its inner surface with a row of four stout sete; palpifer with a chitinous finger-like appendage at its interno-distal angle; about the same length as each of the palpal segments but slightly wider; terminal segment of palpus with no distinct sense-cones. Articulating maxillary piece well developed. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 41 Labium prominent, almost attaining the tip of the left mandible; submentum transverse and hinge-like; mentum longer than wide, arched below, its sides at basal half shightly concave but at its distal half convex, the fronto-external angles produced forward and prominent; palpiger much narrower than the mentum, its sides diverg- ing anteriorly; ligula somewhat thimble-shaped, about the same size as the first pal- pal segment; the second segment oi the palpus more than twice as long as the first and slightly convex on the outer side. Prothorax narrower than the head; anterior margin nearly straight; proscutum represented by two, fairly large, somewhat triangular sclerites. Sagittal line present throughout thorax. Mesothorax slightly shorter than prothorax but just as wide; the mesoscutal sclerites more triangular and smaller. A small bifore spiracle! present in each spiracular area. Metathorax similar to latter but not quite as long. Legs very long, about two-fifths longer than the thorax is wide; cox nearly as long as the femora, the latter with swimming fringes; tibiz shorter than femora and three-sevenths longer than tarsi. The tarsi bear two inner set, one distal to the other; tarsi claw-like and well developed. Abdomen with eight distinct segments, narrowed caudally, ninth and tenth rudimentary. The first seven tergites similar and each divided into three transverse folds, while the intersegmental membrane has only one. The second scutal fold bears a transverse row of four small tubercles. Epipleurite and hypopleurite each surmounted by a small tubercle, not distinctly separated but together forming an elongate laterallobe. First five sternites with three transverse folds and a longitudinal fold on each side of them. Eighth tergite about as long and wide as the interseg- mental membrane preceding. The dorsal region represents the superior valve of the stigmatic atrium and bears a reduced plate, the slender anterior arms of which enclose a median, elongate, non-chitinized area. The caudal margin of the eighth tergite is minutely crenate towards the sides and is rounded in the middle. The rudiments of the four lobes found in other Hydrophiline are weakly indicated. There are two small tubercles, one below and on each side of the middle lobe of this hind margin. Procerci fleshy ard quite prominent. The mesocerci are fairly prominent, as well as the acrocerci. The median lobe of the ninth tergite is slightly bilobed. Lateral iobes not prominent. The prostyles, belonging to the tenth segment, are nearly as long as the seventh and eighth segments together (1.44 mm.) and are superficially annulate. Fuii-crown Larya.—Length, 40-54 mm.; width at the first abdominal seg- ment, 9-12.5 mm. General color grayish or dirty whitish except reddish brown head, sclerites, and legs. Head 6.5 mm. wide; 5 mm. long below; 3.1 mm. long above. Antenne four-segmented,? a small segment about one-third the length of the third segment having appeared between the first and second segments of the first-stage antenna. Lateral expansions of the epistoma not prominent. Mandibles with tips and inner teeth blunt. Terminal segment of maxilla only about half the penultimate in length. Ligula dome-shaped, much shorter than the first palpal segment, which is a little more than one-half the second segment of the maxillary palpus. Dorsal surfaces of the mentum and palpiger with a few scattered sete. iMatheson described a pair as present on the metathorax also but none were seen in the specimens which I examined. 2D’ Orchymont considers that Schiddte was mistaken when he called the antenna of Hydrous four-segmented. There are surely four m H. triangularis. 42 Bulletin American Museum of Natural History [Vol. XLIT Thoracic segments wider than the head. Folds and lobes of whole body much more distinct than in other stages. Legs about five-sixths as long as the thorax is wide. Abdomen spindle-shaped. Pupa.—Length, 24 mm. with cerci (curled up); width at its thorax, 14.5 mm. Whitish. Head smooth, only one small posterior supraorbital stylus noted; two small, oval, raised areas on each side of the epicranial suture near the vertex. Pro- notum smooth, its cephalic margin concave. Styli arranged as follows: three long styli, curving backwards, in a transverse row at the anterior margin on each side; eight shorter ones near the posterior margin, besides two very small ones just inside the inner two styli; a few other scattered ones. Mesonotum and metanotum with a pair of styli in a transverse row. Scutellum well marked. Metasternal spine long. Inner spur of metatibize very prominent. Metathoracic legs long nearly attaming the end of the body. ‘Tarsi not ending in prominent spines nor tibize spinous on the outer side. Metathoracic pterothece visible from above. First to seventh ab- dominal tergites with a transverse row of four styli, the outer one on each side mounted on a tubercle. The styli just behind the spiracles longer than the others and curved backwards. Second to seventh pleurites each withastylus. Eighth abdominal tergite with two small rounded tubercles at the posterior margin on each side of the median line and each bearing a short terminal stylus. Ninth abdominal segment terminating in two superficially annulate cerci about 2.5 mm. in length and with a prominent short, ventral spine between their bases. Abdominal spiracles oval, uncovered and prominent (second to sixth visible). ‘ 8. Hydrobiine Eggs usually enclosed in a silken case with a prominent projection but some- times laid in a mass with a loosely applied covering of silk (Cymbiodyta and Para- cymus) or held on the under side of the body by the elytra (Hpimetopus, Chetarthria ?) or hind legs (Helochares). Larva with head elevated. Antenne with points of insertion situated farther from the externo-frontal angles than those of the mandibles; second segment with an antennal appendage. With or without an epicranial suture; ocular areas flat, elongate, in groups of six, closely aggregated; labrum and clypeus both reduced and united, the anterior margin more or less toothed; mandibles prominent, sharply pointed and with inner teeth; maxille palpiform and stipes with a rudimentary inner lobe. Labial palpi longer than in other subfamilies; the second segment distinctly longer than the first. Ligula present except in Berosus and Laccobius; labium and maxillz inserted at the front margin of the under side of the head! and not attaining the occipital opening. Eight complete abdominal segments and a rudimentary ninth and tenth; the chitinization is entirely lacking, except the dorsal plate of the eighth segment and chitinized patches on the prescuta. Cerci two-segmented but reduce 1 (absent in Berosus). Type of breathing is pseudo-metapneustic except in Berosus, which possesses tracheal gills and a rudimentary stigmatic atrium. All genera have poorly developed bifore spiracles. 1Vestiges of furrowed condition in Berosus and Laccobius. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 43 Laccosius Hrickson This genus is evidently represented by one species and a variety in New York State but the variety has not been described to date. The more common or silvery species is apparently the one which Randall named agilis and was first recorded from Maine. The other, which seems to be a new variety, is less common and of a general brown color lacking the pale triangular space in front of the eye. Both species seem to have a great diversity in size. L. agzlis, although very abundant in its habitat, has been little collected in Ithaca, only three specimens having been recorded to the date of my first observations in the fall of 1918. It is found frequently in Cascadilla Creek either on mud flats or on stone ledges which border its waters. Specimens are most easily collected by washing the vegetation and shore with the creek water, using the hand as a dipper. When thus disturbed, the little beetles will be noted swimming speedily towards the shore and presently observed burrowing in the mud or hiding in the vegetation until they are entirely concealed from view. The most abundant vegetation in their environment seems to be the alga, Cladophora, which is especially common in our swiftly flowing streams. The brown variety frequents mud.holes and swampy lands but, with that exception, its habits are very similar. The life history of this genus is practically unworked! except by d’Orchymont, who gives what he considers the generic larval characters of Laccobius? sp. ?, an immature specimen of which he obtained. This is accompanied by a dorsal view of the head. Laccobius agilis Randall Plate IX The egg-cases of the brown variety have not been taken as yet in the field but those of agilis are very abundant at certain seasons of the year. They have been collected in April, May, June, and July. The most natural place for the cases is apparently at the water line in Cladophora or attached to the roots or blades of grass. They are frequently attached to the rock-ledge itself and, in such condition, are hard to remove with- out breaking open the case. iDr. Adam Béving, however, gave me the following data as to the rearing of Laccobius: ‘‘ Dr. Wesenberg-Lund has not yet published anything about it; Schlick has published a note in the Danish Entomologiske Meddeldser Vol. 4, 1894, p. 304 and alsoin a later volume, as far as I remember Vol. 6; in the same periodical] Vol. 5, 1895, p. 12, you will find a note that E. Rosenberg has taken and reared the Laccobius larva to adult.” 2It differs mainly from L. agilis in that the right mandible possesses only two inner teeth. This s also true of the undescribed larva of L. minutus. 44 Bulletin American Museum of Natural History [Vol. XLII From two to eleven eggs are in each case and these hatch in seven to eleven days. When leaving the case, the larva seems to select no particular place of exit. Specimens have been noticed emerging from a hole in the egg-case proper; others from an opening made at the outer edge of the basal cavity of the filament (see Plate IX). Many larvee have been collected. They may be observed on the Cladophora and stones just where the water laps the shore, half in water and half out, as is the customary position of most pseudo- and metapneustic Hydro- philide. The number of instars seems to be three. About the middle of June 1915 several fairly mature larvee, which were hatched from eggs taken April 29, were placed in the usual terra- rium but, as they did not seem quite ready for pupation, they were replaced. On June 22, while on a special trip to the best collecting grounds of Laccobius, about fifteen larve were taken. The largest of these were placed in the terrarium at the same time as one of the reared larvee but in different receptacles. On the morning of June 30 one of the latter lot had pupated as well as one of the larve of April 29. Upon comparing the larval skins and pupz, they proved to be identical and, so, one pupa was allowed to come through but the other was preserved with its larval skin. Thus, the complete life history was secured. One of the larvee pupated on the surface of the earth, while the other made a cell (6 mm. long, 3 mm. wide, and 3 mm. deep), just below the surface. The dates of development were as follows: April 29, egg-case found; May 4, larve hatched; June 30, pupated; July 3, adult emerged. Soon after emerging the adult’s head, prothorax, and scutellum were colored very dark green, except the lateral margins of the pronotum, which were silvery gray with dark green or blackish spots sparsely distributed. The coxe, trochanters, and femora were gray, but the tibie and tarsi were luteous. The exact time before complete coloration took place was not noted, but it was longer than with other species. EaeG-case, without its filament, nearly spherical, often a little broader than long, its size varying as does that of the filament. Measurements show the case proper to be from 1.4—1.6 mm. in diameter and the filament from 7-10 mm. in length. The latter is continuous with the covering of the case and is therefore holiow, the cavity at its base being quite large, as figure 11, Plate LX, indicates. Newty Harcuep Larva.—Leneth, 2 mm.; width, 0.288 mm. Whitish (trans- parent at first), except the chitinous portions, which are ight brown darkening with age. Integument dotted with slightly recurved spines arising from minute tubercles. Head quadrangular, elevated slightly; labro-clypeal suture weakly indicated by a crease in the integument; frontal sutures parallel, extending to the caudal margin of the head and not uniting to form the epicranial suture; frons quadrangular; hypo- 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 45 stomal margin prominent and there is a furrow in front of it but the labrum and maxillz are united at the anterior margin; gula reduced; the gular sutures fairly prominent and confluent and its anterior margin with two long setz on each side of its median line. The cervical sclerites present. Labro-elypeus asymmetrical, irregularly toothed in the middle with three teeth and with two, prominent, blunt setz projecting from the ventral side. Lateral expansions of epistoma differing greatly; the right rounded, overlapping the base of the right mandible; the left overlapping the left mandible and rounded but bearing a row of stout setze which become shorter toward the median line (five or six are very prominent). Ocular areas in groups of six but rather mdistinct. They are arranged in two parailel rows, the outer one of the posterior row a little out of line and more anterior. Antenne fairly stout; the first segment about two-thirds as long as the second, slightly constricted in the middle and bearing at least two dorsal sensory pits; second swollen a little and bearing a small, colorless, finger-like antennal appendage in addi- tion to the sense-cones at the latter's base, and a long inner seta, arising from a tubercle, as well as a few less prominent ones; third segment very small, almost as wide as long, a little longer than the appendage of the second segment, and bearing three long setze and several sense-cones at its extremity. Mandibles asymmetrical, fairly prominent and stout, sharply pointed at their tips, and toothed on the inner side; right mandible bears three inner teeth, decreasing in size from the cephalic to caudal one; the left has two toothed areas on the inner side, both of which present a pectinate region dorsally, in addition to a tooth. Maxillze with joint-like palpifer; stipes large, swollen, tapering slightly from base to apex, longer than the palpifer and palpus together and its inner surface provided with short, stiff sete, and several longer stout seta at intervals; the more slender set are present at the externo-distal angle; palpifer small, a little wider than long, bearing an inner rudimentary lobe, possessing a seta and sense-cones, below which is a slender seta; palpus with first segment about one-half the second while the third is a little longer than the first two and more slender and more cylindrical; the terminal segment possesses a group of sense-cones at its tip; articulating piece of maxilla well developed. Labium small and with only its palpi exceeding the labro-clypeus; mentum and palpiger very small; both segments of the palpus are cylindrical, the second about three times as long as the first, more slender and with its tip possessing a number of sense-cones; ligula absent; palpiger has two sete on its anterior border near the median line; submentum very indistinct. Prothorax very slightly narrowed in front, larger than the head; pronotum entirely chitinized, except the sagittal line, with a transverse row of sete (about ten) just a little posterior to the cephalic margin, several others on the sides. Meso- and metathorax a little wider and shorter than the prothorax. Mesoscutum and meta- scutum both represented by two subtriangular and very much reduced sclerites, each having a seta in their caudo-medial angle. The mesonotum has two smaller oval sclerites! just lateral of the median line and posterior to the cephalic margin. The spiracle at the tip of a little conical tubercle? in each antero-lateral angle of the meso- thorax two-fifths as long as the thorax is wide. ‘Probably homologous with the cervical sclerites. 2Tracheo-branchies of d’Orchymont. 46 Bulletin American Museum of Natural History [Vol. XLII Legs fairly long, with tibize nearly as long as, but a little more slender than, the femora; femora shorter than the small coxe; tarsi well developed, claw-like, almost as long as the tibize, with two inner sete one distal to, the other. Abdomen with eight prominent segments, slightly narrowed caudally, ninth and tenth rudimentary. The first seven similar, each with two very much reduced, oval, chitinized patches on the prescutum near the cephalic margin on each side of the median line, and four prominent tubercles in a transverse line across the posterior fold of the scutum, each bearing a seta. Each tergite seems to consist of a praesscutum, scutum divided into two transverse folds and posteriorly a very narrow scutellar fold that continues to the spiracular part of the tergite; sternites have similar correspond- ing folds. The eighth tergite represents the superior valve of the stigmatic atrium, bears a large chitinous plate,’ which is about as broad as long. The caudal border of the valve is chitinized in part, possesses setze and presents a bilobed appearance. Procercus one-segmented,”? subconical with a chitinous band on the inside and a group of three sete arising dorsally from tubercles on the apical half. Mesocercus two-segmented and chitinous, the first segment elongate, dome-shaped, bearing a central dorsal seta; the second very small, papilliform, and bearing a terminal seta. Between these two segments in the membrane there are several sense-cones. Ninth tergite is divided into three lobes, two lateral and one median. The median lobe is irregularly dome-shaped with a chitinous plate nearly covering the upper surface while the lateral lobe possesses a chitinous region from which arises two setze mounted on tubercles. Two pairs of sete, arising from tubercles, are present on the membranous area just lateral to the plate, the anterior pair being contiguous with the plate. A ventral pair may be seen through the membrane, anterior and in line with the other two. Acrocercus present on the under side of the lateral lobe and terminates in two setze mounted on tubercles. FuLL-GRown Larva.—Length, 5.8 mm.; width at the second to fourth ab- dominal segments, 1.6 mm. The general color is grayish brown or dirty white. The head, which is 0.3 mm. in length and a little less in width, is often retracted under the pronotum as far as the ocular areas. First segment of antenne little less than the second in length. Finger-like appendage of second segment about one-half the size ‘ of the third, which has become more elongate. Mandibles much stronger. The smallest inner tooth? of right mandible is smaller in comparison with the other teeth. Maxillee more developed; stipes larger and considerably longer than palpus and pal- pifer together. Legs not as long as thorax is wide. Viewed from the side, there seem to be three lateral regions or tubercles on each abdominal segment; the dorsal and ventral lateral regions of the intersegmental membrane are reduced so that only the middle one is prominent. Pupa.—Length, 3.6 mm. (curled up); width at its thorax, 2.9mm. Whitish. Head smooth and bears two supraorbital styli on each side. Pronotum smooth, its cephalic margin lobe-like in the middle. The styli are arranged in transverse rows as follows: ten at the anterior margin, four in the middle at the posterior margin, the two middle ones being shorter than the other eight and the most lateral one on each 1A central colorsess seta noted in some specimens and in L. minutus the anterior border of the plate is emarginate. 2D’Orchymont, because a terminal papilliform tubercle bearing a seta is present, considers that it may be two-segmented. The condition in Hydrophilus obtusatus tends to verify his opinion. 1Indicates a tendency to disappear. Laccobius minutus has only two inner teeth on right mandible. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 47 side a little anterior. Mesonotum and metanotum with a pair of transverse styli. Inner spur of metatibia fairly prominent. All tarsi ending in a spine and all tibize spinous on the outer side. First to seventh tergites with a transverse row of four subequal styli; the outer one on each side arising from prominent tubercles; second to seventh pleurites each with a stylus; eighth segment has two, small, cereal-like lobes, projecting dorsally. Ninth segment has a pair of cerci, which are about four times as long as the latter lobes and project backwards, diverging about 45°. The externo-caudal angles of the ninth segment are prominent and acute. The spiracles are exposed and well defined. BERosus Leach s Schiddte gave the complete life history of B. spznosus and later the larval differences of B. signaticollis. Brocher described the egg-case and young larva of B. ericeps (=signaticollis) and, although he did not rear it, considered that it could be no other species because of its size. At least two species, B. peregrinus and B. striatus, occur in the vicinity of Cayuga Lake and doubtless others would be found if more time could be devoted to their study. These two are fairly distinct; the latter is separated from the former by its usually larger size and by the two small teeth, instead of only one, at the middle of the notch of the fifth abdominal sternite. The carination of the abdominal sternites of the male peregrinus, often used as a character of separation, seems to be quite variable in the specimens examined. The beetles may be taken from early spring until late fall but are most frequent in May and late August. They are hardly ever taken in swift waters but inhabit small pools with an abundance of moneywort, Chara, Elodea, cut-grass, alga, etc. The fact that they are good swimmers requires the use of nets, in contrast to hand collecting so profitable for most of the other genera. The net must be drawn through the water rapidly for, as soon as disturbed, the beetles quickly dodge down to the bottom of the pool and in a moment are buried in the mud. At times many specimens may be gathered by pulling the vegetation out of the water quickly and looking it over carefully. They do not easily escape when thus taken, as they are very clumsy when out of water. In the aquarium, they were observed feeding on the decaying leaves of moneywort, attacking both the upper and under side and eating holes entirely through. While watching them feeding, a peculiar, almost incessant action was noted. The beetles, holding on to the plants with their two anterior pairs of legs, kept sweeping the swimming hairs, which fringe the tarsi and tibiz of the hind legs, down and forward across the film of air covering the abdomen. Just what the function of such a 48 Bulletin American Musewm of Natural History (Vol. XLII procedure may be is a question. Possibly it may serve to aerate the film of air, thus accounting for their ability to remain below the surface almost indefinitely. Stridulation is very pronounced and Brocher considered it in detail. About thirty egg-cases were laid the middle of April in the aquarium on alga and moneywort below water. They somewhat resembled miniature chestnuts in form, and each contained from two to four eggs. The first egg-cases noted out of doors were found May 9 in a small pool on South Hill. The submerged Carex was spotted with the white cases and apparently the dead plants were preferred. In a pool where no vegetation was present the cases were laid upon the under side of sticks and stones. Although more abundant in the egg-laying seasons, com- mon to the family, yet the cases were found during the entire summer. The larve on hatching break through the case at no particular place. However, the most common point of exit was between the base of the flap and the cap. The larvee were very weakly chitinized in com- parison with the larvee of other genera. They spend most of their time crawling through the strands of algze or in the débris at the bottom of the aquarium. The larve are the most difficult of the whole family to locate, due primarily to the fact that they breathe by gills. They live at the bottom of the ponds and farther from the shore than is the custom of the other larve. The débris clings to them and they, therefore, closely re- semble their surroundings. Berosus peregrinus Herbst Plate X Several egg-cases of B. peregrinus were found the latter part of July and the spinning and egg laying proceeded in the following order. 1. An under layer of compact silk, composed of criss-cross strands, laid down continuous with the flap. 2. One egg deposited lengthwise towards one side and covered with a loosely applied silk. 3. Second egg placed near the opposite side, parallel to the first egg and covered with a loosely applied silk. 4. Third egg laid between the first two eggs. 5. A cap of compact silk, composed of criss-cross strands of silk laid tightly over the egg-case proper. HaG-cAseE, as a whole, somewhat chestnut-shaped. The cap end is flat with a narrow flare outside the egg-case proper; and the cap, which covers this surface, is continuous with the slender filament that extends upwards. The other end is rounded. 2220] Richmond, Studies on the Biology of the Aquatic Hydrophilide , 49 The case proper measures 1.6 mm. high, 1.2 mm. wide, and 0.323 mm. long. The fila- ment averages about 4.5 mm. long, its width of 0.13 mm. is usually constant and its sides are parallel. Newty Harcuep Larva.—Length, 1.9 mm.; width at its thorax, 0.32 mm. Whitish, with chitinized areas very slightly light yellowish. Integument dotted with minute set. Head ovate, elevated; fronto-clypeal suture very indistinct; labro-clypeal suture fairly well indicated; frontal sutures gradually converging as far as the posterior third and then slightly diverging, not uniting to form an epicranial suture; gula reduced, polygonal, posteriorly somewhat rounded; gular sutures contiguous for a long distance; labium and maxilla inserted at the anterior margin of the head but the signs of the groove are still present and the hypostomal margin distinctly marked off; cervical sclerites present. Labro-clypeus small, projecting forward rather prominently, arched, with seven small teeth and four equidistant setee. Lateral expansions of epistoma differ greatly; the right rounded, reduced and not exceeding the labro-clypeus; the left prominent, exceeding the latter, rounded and bearing a row of sete on its anterior margin. Ocular areas in groups of six and closely aggregated, oval, arranged somewhat in a circle, each area equidistant from the other except the sixth area which is about twice the distance from the first area than it is from the fifth. Antennz short, not exceeding the mandibles, with their points of insertion widely separated but inside those of the mandibles; first segment a little longer than the second, constricted at its basal half and with a small finger-like appendage, provided with colorless apical setze, at its interno-frontal angle; second segment swollen, only slightly narrowed distally and bearing a small, colorless, finger-like antennal appen- dage, which is nearly as long as the third segment; the latter small, a little longer than wide, and with terminal sete and sense-cones. Mandibles asymmetrical, prominent, sickle-shaped, sharply pointed at their tips, and toothed on the inner side; right! mandible with two inner teeth, the distal tooth much larger than the proximal one, and the vestige of a third more proximal tooth apparently represented by a minute spine; left mandible shghtly notched on the inside towards the tip and with a complicated set of inner teeth, the distal one the largest and triangular; molar area with a small distal, spime-lke projection. Maxille with joint-like palpifer; stipes large, swollen, tapering very slightly, longer than the palpifer and palpus together and its inner surface provided with a row of five, stout, equidistant setze; two slender sete near the externo-distal angle; pal- pifer short, much wider than long, bearing an inner rudimentary lobe, provided with a long seta and a sense-cone, below which is a stout seta; palpus tapering; the first segment only about one-half the palpifer in length; the second much longer and with an externo-distal seta; terminal segment two-sevenths shorter than the latter and with distal sense-cones, in addition to an inner seta. Labium small, with only the palpi exceeding the labro-clypeus; submentum small and transverse; mentum transverse with its anterior angles rounded; palpiger rather quadrate, narrower than latter and about the same length, slightly divided anteriorly in the middle and each half bears the two-segmented palpus; first segment of latter short, the second segment nearly three times as long and with terminal setz; ligula absent. 1B. spinosus has a similar right mandible. 50 Bulletin American Museum of Natural History [Vol. XLII Prothorax rounded at the sides, about the same width.as the head; anterior and posterior of pronotum non-chitinized; rest weakly chitinized except along the sagittal line; prosternum weakly chitinized in front of the coxee; mesothorax and metathorax about equal to each other in size, shorter but slightly wider than the prothorax. Sclerites are not discernible. The pleural lobes are each surmounted by a seta arising from an elongate cylindrical structure (see figure 5, Plate X). A spiracle present in each externo-frontal angle of the mesothorax. Legs long, about one-half again as long as the thorax is wide; coxe transverse; femora and tibise about the same length; tarsi well developed, claw-like, one-fourth shorter than the tibize and with two inner sete. The two anterior cox are closer together than the four posterior coxe, which are about the same distance apart. Abdomen with eight distinct segments, narrowed and slightly lengthened pos- teriorly, flattened above and arched below. Thr first seven tergites similar; indis- tinctly divided into two folds, while the intersegmental membrane has only one fold; each pleurite protrudes and bears a long, slender, tracheal gill, the length of these seven pairs of gills increases posteriorly. The second scutal fold has a transverse row of four setze, each arising from an elongate cylindrical structure (similar to those on the pleurites of the thorax). Another seta, with such a structure at its base, present on the dorsal side of each gill and slightly removed from the base of the gill. Spiracles are at tip of small tubercles. The sternites have similar folds but no tubercles are discernible. Eighth segment short, cylindrical and with two small spiracles! on the middle of its dorsal surface and a few posterior sete. The anus terminates this seg- ment. FuLi-crown Larva.—Length, 5.6 mm. (not counting the gills); width at the second abdominal segment, 1.68 mm. Pale yellowish with chitinized areas yellowish brown. Head, 0.576 mm. wide, 0.36 mm. along the mid-dorsal line. First antennal segment much longer and about one-half again as long as the second segment. The whole antenna more slender. Labium very indistinct. Body gradually widened as far as the second abdominal segment and then narrowed. Segmentation is much more pronounced as is the chitinization also. Mesothorax with two reduced sub- triangular sclerites. Two small horizontal pro-mesotergal sclerites present. Meso- thoracic spiracles distinct and meso- and metapleurites each with a prominent wart- like tubercle corresponding in position to the gills of the segments. Preescuta of meta- thorax and first four abdominal segments visible. Legs much shorter, not as long as the thorax is wide. Peculiar structures noted at base of sete on posterior fold of abdominal scuta replaced by small but distinct, rounded tubercles. The gills are much shorter in proportion to the body and possess no dorsal seta near their bases. Pupa.—The characters used by Schiéddte in his pupal key are as follows: “Motory styli of abdominal tergites in fours; abdominal tergites with a small lateral tubercle on each side; spiracles not concealed; abdominal pleurites not distinctly separated from the tergites; styli of pleurites very short and conical; lateral styli of abdominal tergites very long and slender; prothoracie styli long and slender; cerci elongate, tapering, crooked and distally multiannulate.” The figure shows twenty-six pronotal setze or two more than is characteristic of the Hydrobiine. 1The position of these spiracles recalls the position of those found in the pseudo-metapneustic Hydrophilidz and probably indicates the degeneration of that type. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide ol Berosus striatus Say The stages of this species are very close in form to those of B. pere- grinus and a separate description is unnecessary. The left mandible of the larva is quite similar to that of peregrinus but the right one has only the distal inner tooth well developed. The other two teeth are very rudimentary. As both the species belong to the same subgenus, Berosus, this character evidently is not one of subgeneric significance. Larvee in the National Museum of B. wriceps (= signaticollis Charp.), which belongs to the same subgenus, possess the peregrinus type of mandible but have the labro-clypeus untoothed, rounded and short. The labro- elypeus of B. striatus is similar to peregrinus but the number of teeth varies from three to six. CHZ2TARTHRIA Stephens Four species have been described from this country. C. atra LeConte, 1883, however, is the local species near Cayuga Lake and is very rare. In the field it could easily be mistaken for Anceena and Paracymus but is usually smaller and noticeably hemispherical in shape. Closer examina- tion clearly distinguishes it. The first segment of the antenne is elon- gate and flattened. The ventral plates, fringed with appressed setz and concealing the first two abdominal sternites, constitute the most striking characters of this genus. The life history has not been observed. The structure of the abdomen possibly indicates that the egg-cases may be held on the ventral side of the female, somewhat in the same manner as in E’pime- topus. Hyprosius Leach One experiences little difficulty in separating H. fuscipes and H. globosus, the two species which are present in the Cayuga Lake basin. As the name globosus suggests, this member is strikingly globular in form, while fuscipes is much flatter and more elongate. Both are almost entirely black in color but the reddish brown legs of fusczpes are char- acteristic of that species. They are not very often taken together, al- though they have been recorded from similar habitats. H. globosus seems to prefer the banks of rapidly flowing streams or spring-fed pools, filled with leaves or vegetation, while fuscipes abounds more often in stagnant waters. However, where the leaf-filled pools tend to become stagnant both species usually occur. 52 Bulletin American Museum of Natural History (Vol. XLIL Only the life history of the holarctie species, fusczpes, has been worked out but many authors have written about it. Cussac, 1855, gave the first account of the egg-case and Schiddte, 1862, added the re- maining stages. Miall, 1895, contributed an interesting account of its biology but Balfour-Browne, 1910, must be credited with the most com- prehensive treatise on the species. As yet,a complete description of the pupa has not been presented. The egg-cases of both species are the first of the family to be ob- served in the spring. The earlhest record was April 16 for H. fuscipes. The egg-laying continues in full force until the cases of Tropisternus and various others begin to appear. Then a diminishing in the number of cases takes place. However, the cases may be taken all through the summer and the middle of August brings the greatest number again. This latter statement is practically true of globosus also. The eases of fuscipes are more frequently found away from the bank, attached to floating vegetation, while those of globosus are placed in moss or in mud at the shore-line and usually entirely concealed, except the cap end. Hydrobius globosus Say Plate XI In contrast with fuscipes, H. globosus is uniformly abundant through- out the entire summer. Adults gathered in the spring were placed in an aquarium-terrarium. On April 16 several cases were observed buried in the mud away from the water-lne and only the cap and flare were showing. To the casual observer this white silk would resemble mould. The next day one of the specimens was seen working on an uncom- pleted egg-case. The cap had not been made and there were only nine or ten eggs within it. Upon being disturbed, the beetle stopped spin- ning but almost immediately recommenced. More eggs were being laid and this process was interrupted only when the beetle wished to apply the inner loose covering of silk. This process of adding the full comple- ment of eggs required about half an hour and ancther half-hour was spent in sealing up the opening. It took over an hour to make the broad flare and nearly an additional hour adding silk here and there. apparently making sure the case was properly sealed. Not only did it complete this one case but another smaller case was soon formed next to it and the flares of both fastened together. The number of eggs varies from thirteen to twenty-five but the average number is twenty. The young larve come out the cap end, breaking through rather than pushing off the cap. No attempt was made 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 53 to rear any of them but they were very cannibalistic, constantly attack- ing each other. About twenty-five were left for several days in the same jar and only one larva survived. Some fed readily on the Cyclops in the jar but they were too ravenous to be satisfied. A number of larvee, apparently full grown, were placed in terraria but they would not transform. They burrowed down, making galleries all through the earth, and even formed cells but never pupated. There they lived for several months without food. All stages were found throughout the summer and, in early spring, the partly grown larve were frequently taken under stones, leaves, or in moss. There they were, half in water and half out, lying in wait for their prey. EGG-cASB, proper, nearly spherical and about 4 mm. in diameter. A flat, round cap closes the upper end of the case and it measures 2mm. across. The flare, which is continuous with the cap, varies, but one half of it is usually quite broad while the other half is narrow. Newry HatcHep Larya.—tLenegth, 4.5-5 mm.; width at the thorax, 0.7-0.8 mm. Whitish, with light, yellowish brown, chitinized areas. The integument is covered with small, fine, brown, sete. Head quadrangular, 0.6 mm. wide and 0.528 mm. along the mid-dorsal line; fronto-clypeal suture weakly indicated; frontal sutures irregular but converging gradually and uniting to form a short epicranial suture; frons shaped somewhat like an arrow-head; cervical sclerites present; gula reduced, pentagonal, rounded pos- teriorly; the gular sutures prominent and confluent; articulating maxillary piece distinct. Labro-clypeus prominent, asymmetrical and with five distinct, acute teeth; the outer tooth on the left set apart from the other four teeth, which are equidistant; six sete present, one on each side of each tooth. Lateral expansions of epistoma not exceeding the labro-clypeus, rounded and each with a row of sete at the anterior margin. Ocular areas in groups of six but rather indistinct. They are arranged more or less in a compact circle. The anterior three with their axes more longitudinal while the posterior three have their axes more horizontal and the last, or sixth, area is more remote than the others, which are nearly equidistant from each other. Antenne fairly short, not exceeding the mandibles; just about attaining the distal end of the palpifer; the first segment constricted slightly in the middle and about the same size as the second; the second segment swollen with a small, color- less, antennal appendage and several sense-cones at its externo-distal angle; a long, slender, interno-distal seta present; third segment very much smaller than the latter and provided apically with sense-cones, besides two long, slender set. Mandibles symmetrical, prominent, stout, sharply pointed at their tips, and each with three well-defined inner teeth. The most distal tooth is the largest, the middle one a little smaller, and the proximal one considerably smaller. The molar area is smooth and rounded. Maxillze with joint-like palpifer; stipes stout, tapering slightly ,with a row of five sete on its inner surface; palpifer with a slender chitinous appendage, longer than the first segment of the palpus and bearing a terminal seta at its disto-medial 54 Bulletin American Museum of Natural History [Vol. XLII angle; a single inner seta near its base; palpi shorter, gradually tapering; the first segment narrower than the palpifer and only about one-fourth the length of the second segment; the third is a little shorter than the second and provided with terminal sense-cones. Labium extending forward almost as far as the tips of the mandibles; the first segment of the palpus short; the second segment about four times as long but nearly the same width and bearing several terminal sense-cones; ligula prominent, slender and almost twice as long as the first palpal segment; palpiger quadrate with sides slightly rounded; two long setz in the membrane at the base of the ligula; mentum slightly wider than palpiger, longer than wide and constricted a little inthe middle; its dorsal surface with numerous short spines towards the sides and in the middle; the submentum extremely transverse and joint-like. Prothorax with sides rounded, about the same width as the head. Anterior and posterior margins of pronotum narrowly non-chitinized; sagittal line present, pro- sternum with two large sclerites in front of the cox and contiguous along the median line. Meso- and metathorax the same width as the prothorax but about one-half as long; sclerites of meso- and metanotum fairly large and irregular; the former sub- triangular and less irregular than the latter, which are transverse and each with a posterior T-shaped projection. Epi- and hypopleurites both rounded, bearing a seta surmounting alittle tubercle. Mesothoracic spiracles each at the tip of a small tuber- cle. Two small, elongate, pro-mesotergal sclerites present. Sagittal lme prominent. Legs about as long as the thorax is wide; coxe transverse; femora nearly as long as the tibize; tarsi shorter than the latter, claw-like and with two inner setz, one more proximal and shorter. The anterior cox are closer together than the four posterior coxee, which are about the same distance apart. Abdomen with eight distinct segments and very slightly narrowed caudally, ninth and tenth segments rudimentary. The first seven tergites similar and separated by a conspicuous intersegmental membrane; each of the former has three transverse folds (scutellar fold indistinct) while the latter has only one. The prescuta bear two, oval, chitinized patches, those on the first segment slightly larger than the others. A transverse row of four tubercles, each bearing a seta, present on the posterior folds of the scuta and each segment with the spiracles on little conical tubercles. Epi- and hypopleurites prominently lobed and intersegmental membranes with a single prominent lateral lobe. Sternites with folds corresponding to those of the tergites. The eighth tergite respresents the superior valve of the stigmatic atrium and bears a large chitinous plate, a little broader than long and somewhat semicircular, being rounded in front. The caudal border of the superior valve is slightly chitinized, bears a few sete, and is indistinctly quadrilobed, the two middle lobes more promi- nent. Ninth tergite trilobed. The entire structure closely resembles that of Cym- biodyta. FUuLL-GRowN Larva.—Length, 15mm.; width, 2.96 mm. Color brownish above and dirty white or gray below. Tubercles and lobes of body much more pronounced, as well as the small brown sete covering the integument. Head measures 0.86 mm. along the dors4l line and 1.08-1.2 mm. in width. First segment of antenne about twice as long as the second. Terminal segment of palpus noticeably shorter than penultimate. Prothorax with several, small, dark markings on the pronotum and slightly widened posteriorly. Meso- and metathorax gradually wider than the pro- thorax. The stem of the T-shaped projections of the mesonotal sclerites lost. Legs 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 55) notaslongasthoraxis wide. First six segments of the abdomen about the same width as each other and slightly wider than the mesothorax. The scutella are more distinct. Seventh to eighth segments narrowed caudally. Small round patches composed of tapering sets are present on the folds as follows: six on the anterior scutal fold, the two Inner ones almost contiguous; three on the posterior scutal fold; four on the seutellum; and four on the intersegmental membrane. The pleural lobes also hear groups of these setze in addition to the brown set. Hydrobius fuscipes Linn:eus Plate I, Figures 3 and 8 In the early spring fusczpes is very abundant but, as the season pro- gresses, they are harder to locate. Many have been taken under lights at night and they take flight very readily. Thus their apparent absence from their normal habitat is doubtless accounted for. This absence is evidently only periodic, as they are sometimes quite abundant in the middle of July when the pools are becoming concentrated. Miall says that many pupe of fusczpes are found during July and that the globular cell is formed one-half an inch below ground in mud or clay on the bank. He adds that the adults appear in August and soon lay their eggs. No constant differences could be found between the larva of this species and globosus. H. fuscipes is often a little smaller but otherwise they are apparently identical. No specimens of full-grown larvee are at hand, but I would not expect striking differences in them. The middle tooth of the labro-clypeus seems to be constantly truncate in the speci- mens of fuscipes which were examined, but I hesitate to consider this as a separation character. Hydrobius tesselatus Ziegler A full-grown larva of this species was taken, together with the adult, by Mr. E. A. Schwarz. It was found among some leaves which had caught in the tree-roots near the bank of a swiftly flowing stream. The larva closely resembles globosus and is quite tuberculate. Hydrobius scabrosus Horn All the stages, except the egg-case, are in the U. 8S. National Mu- seum Collection. They were taken September, 1891, in débris in a stream at Bear Creek, Montana. The larva looks very much like a small globosus larva. It differs, however, in the teeth of the labro-clypeus. The full-grown specimen has only four distinct teeth, three to the right and a fourth set a little to the left of the three. The middle tooth of the 56 Bulletin American Museum of Natural History [Vol. XLII three, however, shows an indication of another tooth. The mandibles have three inner teeth but the most proximal tooth of each is very small. The cerci of the pupa are tapering, fleshy, and about equal to the seventh to ninth abdominal segments inclusive. The motory styl of the abdominal terga are four in number and each pleurite bears one. HeLocomsus Horn Only one species, H. bifidus, represents the genus over the entire world. In the field it is often confused with Hydrobius fuscipes and differs principally in its longer maxillary palpus, the last segment of which is shorter than the penultimate. It might be taken for Philydrus cinctus, a common associate, but the elytra of the latter is not striate. Few specimens have been captured in the immediate vicinity of Ithaca and it is only by chance that one collects them. However, they proved to be rather plentiful during May in the pools bordering the Ringwood Road at the source of Cascadilla Creek. Their life is spent under leaves at the edge of the ponds. The life history is unknown but the stages are probably close to Cymbiodyta. CrmBiopyta Bedel Superficially this genus is very close to Philydrus but is easily sep- arated by the transverse mesosternal carina, in contrast with the longi- tudinal keel of the latter. The presence of only four segments in the middle and hind tarsi bears additional testimony of the validity of this genus. In New York we have four representatives of this group, namely, C. fimbriata, C. blanchardi, C. lacustris, and C. rotunda. Of these, the two former have been collected in the vicinity of Ithaca in fairly large numbers, while there is doubt as to the presence of the latter two, al- though one specimen! of lacustris (?) was reported in 1909 by Professor J. C. Bradley. The life history of none of the species has been worked out. Both C. blanchardi and C. fimbriata are found in the same environ- ment and are often taken together. The easiest method of collecting seems to be taking the débris, including leaves, sticks, and decaying matter which accumulates near the shore-line, and washing the beetles out by placing and shaking the trash in deeper water. The beetles, as with other Hydrophilide, rise to the surface and can easily be picked up by the fore finger and placed in the collecting jar. Often they are so 1The specimen is not at hand so I was not able to verify its determination as such, 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide ‘ ~I abundant that they may be taken readily from dead leaves, where the cling to the under side, apparently avoiding the sunlight. They have been observed in both still and flowing water but seemed to be most frequent dwellers in the little pools formed by rain-water or springs. One record shows a specimen captured in moss which was under a small fall in a swiftly flowing stream, but this evidently is not its most common habitat. The best collecting grounds encountered for these two species were located at the base of a steep hill where the rain-water and springs, which trickled down over the surface of a small plateau, had formed small pools. The plateau was composed of a sandy loam and covered with a mat of dead leaves, etc. It was here in the middle and latter part of July 1916, that all stages of C. blanchardi and C. fimbriata were observed. Miss Ruby B. Hughes reported to me the presence of larve, which climbed up her tent-trap,! in abundance. The larve proved, in due season, to be C. fimbriata, as well as C. blanchardi, and a thorough ex- amination of the surrounding area disclosed eggs and pup in unusual abundance. The larve in all stages were found under the leaves and stones; the eggs, in the moss on the bank; and the pups, as well as the emerging adults, in the bank. Cymbiodyta fimbriata Melsheimer Plate XII The arrangement of the eggs laid in the aquaria by members of this genus was rather puzzling at first because of the fact that no czse seemed to be completed. The eggs alone were deposited aad covered by a loos spinning of silk, such as is found within an ege-case, but with 10 outer covering, which is characteristic of the family. On March 24, 1915, C. fimbriata was noted ovipositing in the aqua- rium on the under side of a stone which was lying out of the water. The beetle seemed to be having difficulty and, supposing from its actions that it was drying up, I placed a drop of water in such a position that it would roll on to the eggs. This, however, caused the beetle to leave its position immediately and it failed to return to its interesting occupation. When spinning, the spinnerets are protruded far out and the silk, which seems to be coming from the tips of the organ, is applied somewhat as paint is by a brush. When the drying up began, as noted above, the 'Miss R. B. Hughes was at that time taking a census of the population emerging from damp places by placing a tent-trap and examining the catch at intervals. 58 Bulletin American Museum of Natural History ; [Vol. XLII silk seemed to become more and moresticky, thereby making it appar- ently hard work for the beetle to extricate the spinnerets at the end of each application. Not until several egg-masses were procured in the field was I assured that C. fimbriata is in the habit of laying egg-masses without the usual coverings. On April 28, 1915, at McLean, while collecting in leafy pools where Hydrobius globosus, Paracymus subcupreus, Ancena infuscata and Cymbiodyta fimbriata abounded, I turned up a layer of leaves which were moist*but not in the water and noted a mass of thirty eggs similar to those laid in my aquaria indoors. When these had hatched they proved to be the eggs of C. fimbriata. In none of my observations on egg-laying have I noted an egg-mass laid by a Cymbiodyta that had the usual complete covering; which seems to be conclusive evidence that this species does not add the outer protective layer. C. fimbriata laid from fifteen to forty-three eggs, which hatched out in seven to nine days. It was interesting to note that, if eggs were not taken out of aquaria and isolated, they were usually destroyed by the adults, although I did not observe them in the act. The larve are apparently not as cannibalistic as the larger members of the group and appear not to notice their brothers and sisters unless they accidentally bump into each other. However, one specimen was observed devouring a larva of Philydrus which was about the same size as itself. The length of life history in this genus is probably about two months. On May 19, 1915. two large larvee, evidently hatched from the egg-cases found the latter part of March, were observed in the aquarium. About the middle of June they seemed fairly mature but died without pupating. Although I have not determined the length of the pupal period in either of the two species, it is probably three or four days, as in Philydrus. Upon finding the larve in all instars on the flats above mentioned, I searched the bank to see if the pupe of the beetle could not be located. The first day brought little reward except the ege-masses of C. blan-~ chardi. However, on the second day, fortune favored me and several feet from the water in slightly moist loam and an inch or less under the moss, a veritable array of pup, including more especially those of C. blanchardi, C. fimbriata (few), Dascyllide and Dytiscide, was found. All stages, except the egg stage, were present in the cells and so, by dig- ging carefully and saving the pupal and larval skins, the necessary con- necting links in their life history were easily obtained. 1920] Richmond, Studies on the Biology of the Aquatic Hydrophilide 59 The adults of C. fimbriata upon emerging are light brown below; the thorax is light brown; their head is darker brown; the second pair of wings are gray; the first pair are white; and the eyes quite dark brown. Until fully colored, about two days, the adults seemed to re- main in their cells, as many were noted as being very dark when removed from their underground home. On April 11, a number of adults of C. fimbriata were dug out from the bank of a poo] about five or six feet from the shore-line. This tends to show where the beetles spend their winter days. Eccs.—tThere seems to be no special arrangement of the eggs except that they are usually placed like logs in a pile and.covered sparsely with fine white silk, through which the eggs may be seen. Newty Hatcuep Larva.—tLength, 3mm.; width,0.4mm. Whitish. Head and mandibles light yellow; sclerites of thorax and abdomen light brown (mesocerci darker); integument dotted with minute spines, which are more abundant on the top of the folds than in the furrows. Head square, elevated slightly; fronto-clypeal sutures weakly indicated; frons limited by the frontal sutures, gradually narrowed towards the median line, semi- circular behind; epicranial suture very short, almost absent; gula reduced with its sutures fairly prominent and confluent; two, small, horizontal, elongate, cervical selerites present. Labro-clypeus irregularly toothed, possessing usually seven teeth (the most lateral tooth on each side indistinct), some of which tend to be toothed again, and with four short spines, a little longer than the teeth, regularly placed, arising dorsally between the bases of these teeth and projecting forward. The lateral expansions are similar to each other, with anterior margin straight and slightly inclined laterally. Epipharynx spinous. Ocular areas in groups of six but rather indistinct. They are arranged more or less ina circle. The anterior three have their axes more horizontal and the last, or sixth, area is more remote than the others, which are nearly equidistant from each other. Antenne fairly short, not attaming the tips of mandibles but exceeding the distal inner tooth; first segment equal in length and width to the second; second segment not noticeably swollen in the middle and bearing a small colorless, two-segmented, finger-like antennal appendage, the basal segment small, in addition to the sense-cones, and a single, small, slender appendage at the latter’s base and at the inner anterior angle; third segment a little longer than the appendage of the second segment, which is three times as long and wide as the former, and bearing at its extremity three long sete and several sense-cones. Mandibles nearly symmetrical, fairly prominent and stout, sharply pointed at their tips, and each bearing two inner teeth, the basal one smaller; the left basal tooth seems to be slightly smaller than the right basal tooth; inner surface of anterior piece and anterior tooth serrate; molar area not serrate. Maxille with joint-like palpifer; stipes large, swollen, narrowed slightly towards the apex, longer than the palpifer and palpus together, and its inner surface provided with a row of five stout setze and several more slender sete near the externo-distal angle; palpifer small, a little wider than long, bearing a single, stout, inner, lateral seta, 60 Bulletin American Museum of Natural History [Vol. XLII near its base, and an inner rudimentary lobe, possessing apical sete; first segment of palpus the same length as the rudimentary lobe of the palpifer and a little more than half the second, while the third is not quite as long as the first two together but more slender and more cylindrical; each bears a few slender sete, the terminal segment possessing a group of sense-cones at its extremity. Articulating maxillary piece well developed. Labium extending forward almost as far as the tips of the mandibles; submentum very small; mentum somewhat cordiform; palpiger dome-shaped, four-fifths the mentum in length, bearing several prominent sete dorsally; labial palpus with first segment short, second segment about three times as long and bearing sense-cones at its tip; ligula present and slightly exceeding the first segment of palpus in length. Prothorax with sides slightly rounded, of same width as head. Anterior third of pronotum non-chitinized, sagittal line present, prosternum with two fairly large sclerites in front of the coxee. Meso- and metathorax a little narrower and shorter than the prothorax; sclerites of mesonotum and metanotum fairly large, the former subtriangular and the latter elongate; two elongate sclerites are present in the pro- mesotergal conjunctivum; sagittal line prominent.