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" 2~2 -;; ~ ... -' "0 ~ ~ '" LU :;; -' ~ "" ~ ;:'! C ~ ., ~ ..c ... i Q. ~ ~ ... o --, ~ ., "'"' ... => "" ~ .. i <> c c % .. ~ ... &; ~ % .!: :t: 0> C ~ '" "0 ...... (;AL\Io'OR~IA }'ISH AKD GA:\lE ~~ ~~ It: ::: "'t:'~ ~ t> ....- ~~ . ~~ ~E ~ " ~ ~ .- ~ ~ g: ~ ~: "'" " . ". -,' ". 11 '" I I- I ~ I I '" I .E <. I "2 ~ ~ =< ~ I ,5 .c :0 \.) ~ 0: oj I ] I ::i !: '" I s I ~ I c .. - .. E .~ ~ 0 co ~ .s ,~ I I' I' '-' ~ .:;. of:' 1..,": I~ C ~] _ ~ H) ~ II I ~ I ~ C~ ~ ~ ~ !: I ~ ~ 0 ~, 0 f l:: o ~ ~ ~ o 0 co 0 '" l : I ; ~ ~ l.:? c: "" "" 0 ~ I ~ '" ~ I I 0 t- i ~ ." ." 0 = 0 I co o ~ :2 _ L~ e .",: \: 1- t- 0; p ~ 1 ~ ~ :2 ~, ~ ..:. il '" 'i o '" ] II> ~ -a -g E ~ Ii 8 ~ i ~ E: f .. -E .( .E ] .~ Q ~ ~~ :; " " ~ !i.:, ~ ~ II(. ~ .~ c"'" '" "" a~ Il,"" I :1 o ~ .. ~ ~,~ ~~ _ e l::~ ~ .. E '; c - ~.~ Q .. ~ .: '-' s:: 5 "8 ~ ~ ~ '0 ,3 '0 t< C .~ ~, :SU o o 0 0 ct ~ ~ ~l ~ co ~ 0 0 I!,:, ...... CICl (CI C J l I ~ ~ ~ e. o I"': e:\I c: co ..... I ~ I t: I.-~ -t1 0 ~ ,~ ~ '.":' I~ I~ ..., 0 '" 0 o I~ N C ~ ~ Iii o .,,:: ~ r c ~ ~ ~ ~ I I I II "' .E ~ i 1 ] ~ c;] e .: 0 c ~ >'.~ u i;C] I ...... ~ ~ I .2 i5 ~ ~ ~ ~ ~ >. c. f ~ C .0 bl. " " ~ 1~ or; ~ ~ ~, I ] I I '" .. ;: 0: ..;, ~ -g i ~ <5 Ci ~ ,,,, t: ;.... 1 e i:jji . " .;. .. .: E '0 ~] "Cl'::' ;'~ ~s -'5.,. f.s ~ .. ~~ il f "Cl.. ':12 " 0 ,.5Q ...... c '-' e ~ ~ II> > j .,.ti. ". fl ~:) :;,~' 'r,. ~' ~' ,',..',,' " .t'\; :," .:. . "'1' .~ ',', ',:i , .' >.\ ,i.. ,i- ' NATIVE POSTLARVAL FISHES 283 >. anal rays in both sllcl,l'rs lInd miuuows, and olSsifiation of the pectoral rays also Occurs at this time. A peculiarity of the Catostomidae is that the operculum does not completely cover the gill arches until stages :n to 39. Catostomus commer'soni (Lacepede) alsO seems to tit this gen. (>ral picture (Stewart, 1926). The cyprinid stages of Balinsky ma:r stand, therefore, as a basis for cOlllparison of .Americau minnows aud suckers. ARTIfiCIAL KEY TO POSTlARV AL fiSHES Most of the eharacters described 111 the key, that foIlo'ws may be readily seen in the accompanying photographs (Plates 1-4). Difficulties were encountered at three points in the preparation of the key (items 4a, 8a, and 9a-9b). No small specimens of Ptychoclleil1ts l1lCius were cullected but it is assumed that they possess characteristics noted in late postIarval stages of Pty(~hocheilus grande and P. oregOllense. Those two species have an oval internal pigment spot near the base of the upturned portion of the vertebral column, as in Gila robusta. \Vhether l'tychocheilus can be separated from Gila in earlier postIarval stages l"l'mains to be determined. To our knowledge, Ptyclwcheil1ls now occurs only in the main, swift flowing' rivers (Colorado Rh'er, Salt River) and does not go up tributaries very far. Consequently, cyprinids from smaller streams that key out to item 4a can be ideutified with confidence as Gila robu.~ta, . The species within the genera Catostomus and PaJltosteus are often difficult to distinguis)1, even when adult. '1'his problem is greatly multi- plied when one attempts to key out the larval stages. We feel confident that the separation in the key between these genera is well founded, but it has not been possible to separate the species of Pa1ltosteus and the distinction between Catost01ll1lS insignis and C. latipinnis is weak, although juveniles can readily be idt'lltified. III general, C. latiptnni8 seems to have less pigment than C. insignis. As with l'tychocheilus, few specimens of C. latipinnis ~ave been recorded from the Gila River drainage in the past 50 years and, so far as we know, this species does not go far up the smaller tributaries. Consequently, suckers from the smaller streams that key out to item 9 may be determined pl'QvisionaUy as C. insignis. Pantosteus dephinus, recorded here for the first time from the lower Colorado River system (Burro Creek, tributary to Big Sandy River, Mohave-Yavapai Co. line, Arizona; UM:MZ 165920), has been taken only once in the Williams Iliver drainage, tributary t.o the Colorado Ui\'er at Parker Dam. It is evidently scarce there, whereas Pantosteus species is common. la. Distance from front of anus to end of cl\uulll fin enters llistnnce from an- terior point of heall to front 0' IInus less than two times , MinnowlI, family Cyprinidae 2 11.. Distance from front of anus to end of caudal fin enters distance from 1lD- terior point of head to front of anus more than two times Suck",.., '.mil)' Catostomidae 6 2a. Pigment on medial edges of nares concentrated as a single or double row of chromatophores. lnternarial region largely unpicmented. Pigment line of horizontal myoseptum utending forward nearly to bead ., .A"ON cli,.".o"..en (Pl. lA, Pl. 24)