Se Te¥ ty ee AS FoR ; ee ot ee nodal nik beat Sete oe | 3 yee esoksnoliag’ bedqaroantt Kovs pote Louis i etate atontist dg 20 ‘i “sstongnar? ox phved. nottalt efoatiil te ecatentas boot to ‘ : a bib ath, Atty LS a ws +anr £ ade ‘48 t 568 (or a tr $ ge sie ge Wh thes te) eo ee -noegqmertT ge dived ; sneberses: at dtwow ovisaled .2 Be eae AUER OE af wee? t bes a veOns ‘yuasda Bi | Met dnLey at Ww porttd BLiM oiatent be olidemotus on? 68 SER aL fg ce Sie a Eee est ot F Poi a eats ‘ (te Lovet ago adi 0) 8 opetecetike suogen A 48 he , G6eL 2Q9 Bet i Dor: a | , ane peor "oaeaofaot Sobor! an. age ea bain ae “OEE * nce abort tes is hes post »4 de ¢ we x02 actolseengue » ‘al wera LET ft sy $9 et esecont «i re a" { aie « RELATIVE GROWTH IN POLYODON 1 ee se ey ee - “ - 6 Sad David H. Thompson carte at SPATE OF ILLINOIS ' REE, of Beet pars*ien and Education Division of the NATURAL HISTORY SURVEY Theodore H. Frison, Chief bes ety eae Mae 4 a I q he 2s ; » we i L. oes _ 7 ¥ NOTES NO. 2 URBANA, JANUARY 1, 1934 20 P * nS eaet 7 ane Os o OE a order © 4orenss omy 3 : f ry ans a, } ia i a Sa a? et ve ys: ; ie Kr . ; ee res. ir ', »! ey. rs . » : 4 ne. ; nab : ea roy 1 Ve) 1 A Ae | *OMOY.IOT UI RTWORD ‘avenaaa i” : ee em teem ein peae 7 ¥ * eames es aay ; Fetoteen fats rare POS eerie % aocqmodT .«H bivac ay - ne a : i , : . : i‘ a | 5. ‘ 7 bl = ~~ : - - |! nd Se aoe ane kad at Teer. BPs Ure AaRMRAIA SH. STARE yo decent Te nae nottaovks baa ngdtendatgedsteitcomreqed 79d: We pOkekv IG oer i | amg oy | tefdd ,nortxT .H sioboedT bee 7 ‘ J iz is : he oF ay e ° ; fe AS % vse oe Wee fake ue beeL .f YHAUWAT (AM ASAU Relative Growth in Polyodon David H. Thompson Rostrum.—The spoonbill cat, Polyodon spathula (Walbaum), has a broad, thin, paddle-shaped rostrum of cartilage enclosed in a loose network of bony splints. This great rostrum with its many sensory endings serves for the detection of plank- ton and other small organisms on which this fish feeds. The mouth is unusually large and the gill arches are furnished with numerous long gill rakers which strain out the food organisms as the fish swims about with its mouth open, It swims unceasingly with a monotonous rhythm and swings the rostrum from side to side in a wide arc, It has been supposed that these movements of the rostrum are of use in beating small animal life from vegetation in weedy lakes, but there is no evidence of any active digging. Distribution.—Polyodon inhabits the Mississippi River, its connecting bottomland Jakes and bayous, and the lower courses of its larger tributaries, including the Ohio, the Missouri, and the Illinois. It is a ganoid and resembles the sturgeons more than it’ does other native fishes. It has only one living near relative, Psephurus gladius, a large fish found in the Yangtze River in China. A fossil form, Crossopholis magnicaudatus, has been described by Cope (1883, 1885, I886€) from the Eocene Green River shales in Wyoming. Fossils of two specimens about a meter in length show snouts shorter than those of the two living forms (Dean, 1895). Measurements.—In May, 1952 we collected seven larval specimens Of Polyodon (Thompson, 1933) from which the length of rostrum and of body were measured. Extensive series of such mea- surements are given by Stockard (1907) and Danforth (1911). Bar- bour (1911) figured three specimens which have been measured, and Doctor N. Borodin has kinily furnished me measurements of three very small specimens in the Museum of Comparative Zoology at Harvard, Nichols (1916) published the measurements of a very large individual, These have been supplemented by measurements of other. specimens in the collections of the Illinois Natural History Survey. Since these data form an unusually complete series, they show in some detail the relation between the length of rostrum and the length of body. This comparison of relative growth is of especial interest, since the rostrum is relatively very small in larvae, relatively greatest in specimens about 250 millimeters long, and becomes relatively shorter in larger individuals. The data are especially significant since the range of sizes is very great, the largest srecimen being 127 times as long as the smallest specimen. Throughout all these sizes the spoonbill is free living, has no abrupt metamorphosis, inhabits the same waters, and fecds on the same food. The following tabulation shows these measurements ar- ranged in order of increasing total lengths, The rostrum and body ns / : ‘ ; oi = _ , i 4° . Ri: i a” » moboylod at dtwor evitsleA - is nee _ —_— @ ee wr ~ “ —- IOWA To NOL odie oH "bevel aludtaqe amohoylod feo. Thededene ‘eiiT—. 20H eel tung Te AaTiee? ootaaaen ee eg 1. Poe puriteot sete gta: opetert Loe -ig “19, pltowsen erool 8 a 2 nate “to Soteostsi oat sxe aerRee ; saretnee oaae2 gna ett ats __, Oat’ ‘ebest deittétdt dotdw -cio- ome tae ayo a «oto Sis- ‘At tw. bese Eni’ - ‘84a esdoes Ifta ent ‘asmel zok -yi tates ef sifsen aR, ame Ley t6 * ‘hod? Sit dvo niaazte dotdw cieket , fa ‘gitol’ coe “elaotége otis’ emiwe 2: -yaeqo.dtsom ett dt suodi aa@tue dett opie. ‘ot ‘DIZ M64 aureteor oft -egatwe bas o 45*28UR dt onom a dein Gtk 10. "gtiemevom seerit. dadt beeoqque mogd sad: nit: 2} : Ue : + roe . gies haa il fj Polyodon Measurements Length of rostrum to Length of body from Rostrum as — per..cent, of Sources front of eye|front of eye] body length mm. mm. inm moa. Neat. Hist. Surv. Pie 1.5 15.5 9,7 bs nell ‘ . 17.5 152 16.3 7.4 ay : . “4 18.5 1.5 {2 8.8 " . - . 19 1.6 17.4 9.2 " e " " 19 V7 17.3 9.8 Ny 7 ¥ is 20 a 18.3 9.3 ba be : i 20 1.8 - 18.2 9.9 Borodin St 8 29 B12 “ 57 15 42 She ” 60 19 41 46.3 Danforth 74 22 52 £P 4S Barbour 80 24 56 42.9 Danforth 89 26 63 41,3 " 104 34 70 48.6 ‘i 107 34 73 46.6 Barbour 130 46 84 54.8 Danforth 140 48 92 52.2 n 144 49 95 51.6 " 170 58 112 51.8 . 175 58 ny 49.6 n 200 78 122 63.9 Sil Nat. Hist. Surv. 200 69 131 52.7 a, : : " 212 % 141 50.4 " " n m 215 69 146 47.3 " " . 4¢ 220 71 149 47 7 " " " . 225 78 147 Boal m " n " 226 80 146 54.8 . ‘s “ : 227 82 145 56.6 hy " . ® 229 75 154 48.7 " " " " 230 79 151 5245 . ¥ " " 33 78 155 50.3 " " " " 233 83 150 55.3 ." A " R 235 82 153 53.6 - mn ws m 240 89 151 58.9 .* " n * 241 77 164 47.0 " : : " 248 83 165 50.3 " * s " 250 92 158 58.2 " . ” " 252 88 164 5SeT " " ¥ R 255 87 168 51.8 n " " " 261 89 172 ny n " " , 263 92 171 53.8 " " " " 266 85 181 47.0 " " " " 267 89 178 50.0 n n " ft 270 92 178 51.7 n " n " 277 102 175 58.3 eh al ee ee ~*~ ~< -s } ar Th. 4 ae pnts ae ks * * “Dats Oearard em abel cad td » a < peping oy < = 3 nS par dy wW>s ie bear 4 $6 Pht eS aos . . on oe 5. Sen BB on v8. : eB. fs = > Aes aad .vure -toth ot mit wt, eet on an O hid we wit on nw? mt nt ex wt sae = % “sae See ease im Polyodon Measurements —continued Length of Length of Rostrum as . | Total {rostrum to body from per cent of Sources length |front of eyejfront of eye] body length _ * . mime mm. TAM» Tll. Nat. Hist. Surv. 410 131 279 47.0 ESI . . 453 155 298 62.40 - Ne ' r 514 152 362 42,0 , . s ‘ 515 173 342 50.6 EMF © a 526 177 349 50.7 oe ie " " 528 Ly 351 50.4 - tt 5! " 531 180 351 Mls: “ ‘ : ‘ 540 175 365 47.9 4 x " : 543 160 383 41,8 a i ) 558 185 373 49.6 "4 . . ? ST 188 389 48.3 Stockard 5 is 610 203 407 49.9 T1l. Nat. Hist. Surv. 621 199 422 Bgl a . , 632 197 435 A545 ‘a " a . 752 236 516 45.7 Stockard 7.62 229 Bao 435.0 -." 914 259 655 39.5 Barbour 914 245 669 36.6 Danforth 1,000 260 740 Seb * 1,030 290 740 39,2 4 1,050 310 740 41.9 9 1,070 + ..260 810 $2 1 J . 1,090 300 790 38.0 Stockard yale ta 305 813 woT eS “Danforth 1,180 320 860 3762 < 1,200 340 860 39.5 e.." 1,210 330 880 S155 . 1,210 310 900 34.4 Stockard 1,245 333 912 36.5 a 1,295 3435 952 36.0 Danforth 1,300 330 970 34.0 Stockard 1,346 343 1 0S 34,2 > " 1,499 356 1,143 Shek 4 1,524 404 1,120 36.1 ‘< 1,575 406 1,169 34,7 ‘ 1,600 400 1,200 5395 f ‘1,600 419 1,181 55.5 i 1,676 400 gee Slee 4 1;5'202 432 1,270 34.0 . 2,755 454 1,299 34.9 “Nichols 2,159 432 1,727 25.0 a Cape #, aS Pees Baan in —— 000 hte 2 a orf TV3:-3 Ola: bet aie | [s6.. ovwe etelh SoR2* * SéBc- ‘ Sat =. AIG.” x. SIGH ge 00042 Yet : pee et os = . J 020, if: ~ OMOLf 3. oe0; nT eae Bll, OB " vw san: abe Loe e 4 oe “ = ss — u - ut > 1.4 Cw ¢ ~ te by Cc . ava, isct SOP, L280. 4 ra es Cdl, Oo > Wy 4 were measured from the front edge of the eye in order to be able to include published measurements. The eye is a well-defined base of reference for measurements in fishes and is particularly useful in growth studies since it is differentiated very early and is firmly anchored in the chondrocraniun, Differential growth.—In the accompanying figure, fp. 5, the measurements o € length of rostrum are plotted against those of the length of body using the same logarithmic scale, An examination of the distribution of these points suggests a curve rather than a combination of two or three straight lines. Hux- ley (1932) has described a number of relative growth curves in | which one straight line breaks abruptly into another straight line with a different slope. He also shows instances in which one straight line breaks into another through a short curve. May it not be that all such relative growth curves are hyperbolas with asymptotes crossing at varying angles and approaching these asymptotes more or less closely? It appears from inspection that the Folyodon measurements lie on an hyperbola whose asymptotes . cross at an angle of about 135 degrees. A smoothed curve has : been drawn by selecting the point where curvature is greatest and by drawing a symmetrical curve to the rather straight limbs at either end, The upper end of the curve, representing measure- ments of the larger specimens, is almost straight with a slope of 0.68. The lower end has a slope of about 4.1. this differential growth within the rostrum of Folyodon, the length from the barbel to the eye was plotted against Body Téngth. This region was found to grow at the same rate as the body. Therefore, from the standpoint of relative growth, this part between the barbel and the eye will be considered as part of the body, since all of the hetérogonic growth occurs in the part distal to the barbcls,. | In order to learn something about the distribution of . ; The distance from the posterior edge of the eye to the tip of the opercular flap was measured on the specimens in the : collections of the Illinois Natural History Survey and combined with other measurements made in the same way by Danforth (1911). When the logarithm of this length is plotted against the logarithm of body length one obtains a curve of heterogonic growth similar to that for the rostrum except that it shows smaller departures from isogonic growth. The slope of the lower limb of the operculum curve is about 1.9. It reaches a value of 1 at about the same body size as does the rostrum curve, and then declines slightly. Tad Barbel length was also measured throughout a wide range of sizes of spoonbill. When the logarithm of the length of barbel is plotted against the logarithm of length of body it may be seen that its relative rate of growth is at all times slower than that : of the body within the size range of fishes used. The barbel a curve begins with a slope of 0,7 but, in body lengths exceeding } 100 millimeters, it has a slope of only 0.5. It should be mention~- 4 ed that the barbel, like the rostrum and the opercular flap, is olde ed ot tebs0 at oye edd to eshs. Snoct ods MOLT Bowesen 67 1a 25 Sbcitetaliéw ret -by eo? , bvsmett eset bedetigug ebuiont pom «Bog reateaSenBq' et Die edfe pa Pere ePaR awed O's ottete 1S 1 14 oead a fie Lia NS tN Ro BB19 Th yet ED bao FL2 BSN AOR MASSE Ht HORy SP iviess = ude ges fbadaatse-ts at phabé asia ee eee vingt3* ist bas. ey ay tHaeeouerns ot Bll ata SS Seo errua tt artes BqmO908 3.8 — eae 425 BRS Gent ‘peaguig? + re dur? west Tot sts Teneiwesem J pea! 834 (Bet! 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LAQSOSSG2 (9 Row? - BBO BGSY FFT iy (oaeise Baot te etea estotamyes anit AOLEOUSMRY HAT SaBih9 STII Gy AL He 'R6°992° etHBnisted asin ‘Roboweba oe | « B tOd A MMAS ONS DeAOSGALA “SeseTysh BST MMedB"to ¢ ail SVMS efed Te tbc) owas Tae ah68- 60d gH it so 68 Sg aws %5 ePottselloo 1s siljoorebjyedrestisditeledd éane sts natidghes attomaacesst 4daee daw iit {BAe * sas tee Tare heesose of HMistets BIte Yo “eos FSIOl~4aF comw be esl biteldiwoess St4dseddoRadaoetaHsth AG tard Tan - iputet- ‘¢bod to | ual! RORY PEMS 8 “genouad= ‘dwSGe IF 2 MeAs ESZABRO GUOITHS SAP ANGE FBAdt OF — anNLenenge sai Moada rs ttove [* Belt TASS LOUTIROS, MiP oO%O? oAegoB? mod — pombes Gade ieiPeIsodaes O Yo Sythsi8 BSToneP ¥OT , S107 08a eT ovary By aks. Oct » PH MTRS “e, Ake S¥L Avo FP PASS rise winded! oat Sao 5B ee oxtg | cyiddnkse PUN ELON ath Da, ORR RSS SS GS ass A eee - ne 2 ie = . ol w A at a Hip he tr ay ee hs ee vex Pa ts made up essentially of cartilage and skin. I should like to emphasize that the rostrum, the opercular flap, and the barbels each show declining rates of growth relative to the rest of the body. Discussion.—Assuming an earlier stage in the development of Folyodon than has yet been discovered, a stage in which recog- nizable rudiments of the rostrum, opercular flaps, and barbels have not been differentiated, and keeping the relative growth curves of these organs in mind, an examination of the 17 millimeter specimen suggests that the barbels are differentiated first and go through an initial period of rapid development followed by declining growth rates relative to the rest of the body. Subsequently, the rostrum and opercular flaps are differentiated and grow at high initial rates which decline to the rate of the rest of the body or lower. Since barbels, opercula, and the rostrum each originate from cells, or groups of cells, with the capacity for synthesizing cartilage, it seems likely that the growth histories of these organs may be expressed as an equilibrium reaction between the total amount of growing cartilage in these organs and the concen- tration of cartilage-forming substances in the blood stream which feeds this cartilage. Folyodon feeds on the same food throughout its life. Hence, it may be supposed that the digestive and assimilative pro- cesses remain the same throughout its life and, under comparable environmental conditions, that the amount of cartilage-forming substances put into the blood stream is closely proportional to the size of the body. Thus, we may expect that the actual concen- tration of these hypothetical cartilage-forming substances in the blood stream is greater in early stages of development, when there is little or no cartilage, than in later stages when there is relatively much cartilage to use them up by its mere subsistence, The rate of growth of these cartilaginous parts may then be expect- ed to decline to the rate of the rest of the body, While the assumption of an unutilized excess of cartil- age-forming substances may account satisfactorily for the high initial growth rates of rostrum, barbels, and opercular flaps, and for the subsequent decline in the relative growth rate of these parts, it must be modified to account for the fact that the barbel curve has a slope of 0.5 in the same fishes which show rostrum and operculum slopes of approximately 1. In order to account for such differences in relative growth rates we may suppose that there are intrinsic differences in their component cells as regards their rate of multiplication, and since the barbels are attached to the rostrum, we may suppose that these intrinsic differences arise by some process akin to starvation. The same sort of explanation may be used to account for the decline in the rate of growth of the rostrum below that of the rest of the body. Folyodon shows an increasing proportion of rostrum until the fish has a total length of about 250 millimeters after which the proportion of rostrum declines. It has already been mentioned that the-heterogonic Ly) Se : ey at ies . * oe Paes! x 4 t. ek * ae r > oft ePfi HivoMh D7, atin hie syal tino t-te tee elodead “gas Berd faery iat nsaete. ont ; ott Yo taos ‘ett OF ‘oI Bled dfworts: et achat ao Fat “GHEntiesbh toni, = - or = meer 2 trengoietsh ots ofemste i fleas -cee antimitiqhee .motsadné fe -go0et-righdw.nl eyste @ i fbsievoos {6 ‘Heed- Sey ear mid cobe¢ hs even thedtad ‘pase (eas 1% i Wa kise ade” wimetheet Gat te ‘gio tB “9. be advise iithonl evid sied eo At Snitqsou ‘Bie dota retest FE6 emtoeqe “tePotitl lin Fiat to noftaitinese ac Bez for ° ivy oe Hguenit cos ‘bas Servi? “ete brislet? ota efedtsd o anintided ‘yd bowoLle?. jmongé lve “higet- te poh” tebe ssf ait Hitnadgeesise s” /ybod W64t Te "teds 15a¥ oF owt s¥or eotat Ss dg id te wit “Brit Bets ftisee tt es oid aqelYdtslugteg? tae Bes vhod “het! tot sist: “ast: Lo “odt@r val oF ‘ott ised do btw yoda” PES stants Pio didi “aes Oe iif Bria (eluonees “fetedisd sents’ ~ grewels ants twolneces’ EO Kos as ORE dt'hw Jellad %o ‘ngsots'4o_ etiss 3 oRods "tee s'Piaie A chtwory “ie Sais eisute ¥nser- st 293 : pe ent reid tet ‘OTS Swe BMetice Ef Toble- ‘aa 2a" “bores 'rixe ods yar Ten" “MOOSE SiR? 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Cds telat eee” +e: aol? 68624 SRT ese) Sree eatgei ¢ Ae Solo x6G oH Sei ce hite! isFta* erotomt ri ts OBS" tuo0ds_ 2 oltog teers igvit tak Hsvottivew' head ybssaciad ede* 935° | poate a 4 growth of the rostrum is limited to its distal part. One may look on this distal part as a growing tip—that there is isolated in the tip of the snout of a spoonbill larva a cell, or group of ' cells, which grow more rapidly than do those of the remainder of the animal; furthermore, that this cell, or group of cells, is carried forward by its own growth leaving behind it cell descen- dants which grow at the same rate as the rest of the body, i.e., more slowly. Since this growing tip apparently has the capacity to produce cartilage at a greater rate than its cell descendants in the same concentrations of cartilage-forming stuffs, it will tend to build up a surplus which cannot be maintained at an isogon- ic growth level once this growing tip is destroyed or is changed in its growth potentialities. As the gross amount of the cell descendants of this growing tip increases relative to the rest of the body, the blood supply reaching the tip must traverse more and more cartilaginous tissue and hence may become poorer and poorer in cartilage-forming substances. It seems reasonable that this starvation will reach a point where the growing tip is either destroyed altogether or is so altered that its cells no longer multiply more rapidly than those of other parts of the rostrum. As one inspects the outstanding anatomical features of Folyodon in the material which we have available, it is apparent that the rostrum and the opercular flaps are the last organs to be differentiated. All other organs and major parts already have made their appearance and have passed through the initial stages of their growth history. We should look upon the heterogonic growth of the rostrum and the operculum as the normal growth beha- vior of parts which have been delayed in their differentiation while other large organs of the body have already been differentiat- ed and have come into growth equilibrium with each other. The rostrum is in a variable and unregulated condition, It may be looked upon as an organ which has been recently evolved and not yet coordinated with the rest of the body, or else, while it may be quite old, it has not been subjected to rigorous selec- tive action. As one compares a series of specimens of Folyodon of the same body length one finds that such anatomical features as body contour, length, width, and insertion of fins, size of eye, and expanse of mouth are very uniform and fixed in their proportions. In contrast with the fixity of these.morphological features the length of rostrum varies widely. It is apparent, however, that individuals with short rostra show a compensating increase in width. The lengths of opercular flaps not only vary from fish to fish but are usually different on the right and left sides. The rostrum of the spoonbill, as compared with the snouts of other fishes, may be considered as an organ which has undergone great changes since the ancestors of Folyodon split off from other fishes, and is twice as large as that o 1eé Eocene spoonbill, Crossopholis. a - * ca a fe Fp or v . ‘ ot 3 Sole : t * : “ae ces sng ar® oa ia ‘, ue teae2oe 9% = Renee pat cote. | a x: © todt, “Pam, snp: ox dy Os ‘ass ‘et; Bipot BT hy P ter ett, 50 3 i wea ar ‘thi alos: gh Apatite nrgmot: % ef traq. ete lb #tit so “To quvoug: to: tee @ by ‘tal il tdepoge(@ tO" + ptosis 1a 2: teba tenon rots 3 ero “ oh. cree) eiblgnt BM 20%; : fa tele: bas sau ige BYGICE IS: 6s: pekdoF2 dest AOC (£00 aa gE; ate 3 hosed yee FF | Sobers '@ quran they e se] baties R: ebro” ing #4 . Relies avif rare’ (ane Rio Sania Cts ie Ja ebul b> one ‘hal thot quae pit TC iy biog pate ge Pa: to net Jasbir t “beyp: , it bibw 12h Bites. atwotgen ghod ee Thane Sh Perit bine dior Tis, URON sce Gon? tb erage 2+ Doses {oR Pei trototaagn, pebit Te-vFh ft, oat. dt tye: se aetnes Tr olicong, 5 it 3 . ttroweggs. .Q@4 #1 “A Ytebiwe eg itey gusta20% a6" Rate is eqxat = @ wits ae (aggiiog, e-wosle H4eeod" 4 toile taaw: ‘eitebitto dacs: -prover$a > yikt x fio. tog-: ‘egal: Hal Usted “Fo pétgas bach FE gt Sasete i? | tts-t*orfe" 3h Eee terkt to ate" nT EB acter: ts" “Bud tert os -igth de@et aside’ asi gidity: dipiesqiiod* eA a Lidaoege ant: Ty mutt RO © FRx: orients t ay, “ead. Hoty re te ns ‘Ba. bocahiauon od'-ysn "home ts. sive Isitt O Yost". AAR tiversoboYlot Yo atotesona orld sonte 9a ft tWnoeqe ensoot 6: Oo tact er wane ea eotwt ai bie -chitaee . Beret * The sturgeons are the nearest living relatives of the Folyodontidae, and, since sturgeons have snouts about the same size as that portion of the Folyodon snout between the barbel and the eye (which we have already shown grows at the same rate as the rest of the body) we may look on the remainder of the Folyodon rostrum as something added to the essential organization of a sturgeon-like fish. Since this added part appears late in develop- ment and is recognizable only insofar as it grows faster than the rest of the body, it may be considered as a sort of benign tumor which has become partially fixed in its characteristics and is in some degree useful as a bearer of sense organs for the detection of food, Like a tumor it may be removed without seriously hampering the welfare of the individual since we have found a number of specimens with various fractions of the rostrum cut off and healed over, as far back as the barbels. BIBLIOGRAFHY Barbour, Thomas. 1911 The smallest Folyodon. Geet, Bulls Vol..21, pr. 207-208. Cope, E. D. 18835 A new Chondrostean from the Eocene, erer., Wet, Vol. 17, pre 1152-1155. 1885 Eocene paddle-fish and Gonorhynchidae. Amer, Nat. Vol. 19, pr. 1090-1091, 1886 On two new forms of Folyodon and Gonorhynchid fishes, from the Eocene of the Rocky Mountains. Mem. Nat. Acad. Sci. Vol, 5, pp. 161-165. Danforth, C, H. 1911 A 74 mm.Folyodon, Biol, Bull. Vol. 20, pp. 201-204. Dean, Bashford. 1895 Fishes, living and fossil. Columbia Univ. Biol. Series. III Macmillan and Co. Huxley, J. S. 1932 Problems of relative growth. Methuen & Co., Ltd., London. Nichols, J. T. 1916 A large Folyodon from Iowa. Copeia. No. 34, p. 55. Stockard, C. R. 1907 Observations on the natural history of Folyodon spathula. Amer. Nat. Vol. 41, pp. 755-766. Thompson, David H. 1933 The finding of very young Folyodon, Copeia No. l, pp. 51-353, ond, to ep wliabert jy iv it ise art, ata. 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