122 



Bl'LLETIN of tiik united states fish commission. 



Viiriiitlons," tin* iiiiinber of rays in tln'so streams (U'<;ioas«'s with the altitiulf iim: 

 swiftness of the stiraiii. .Moreover, tiie I'acilie streams of South Aineriea have Ntil 

 slioiter ami presumably still swifter streams, ami no such modi fieatious are seen ii 

 the fishes inhabiting- these waters. 



The most striking ease, that of Lrncisciis {/{iclidnlsonius) is explained uiore full 

 in the eliapter on loi-al variations. In tiie subjjfen is liicltartlsoinHfi, vnufiiml to tli. 

 Columbia and to the Kraser systems, the nundu'r of anal rays varies from IL' to :" 

 an inerease of fnnn 1' ti> l."» rays over Lciiriscm, sonie of who.se species have aN 

 reached the headwaters of the Cohunbia, but who.se Jisiial habitat is the Atliiiii: 

 slope. The jjenus Oiirorln/iwIiiiH has a similar increase of anal rays over Sahiio mii 

 iSidfcliinis, wiiicli are jU'enera of wider distribution, some of the spe«'ies beiiiff fuiii; 

 on the Atlantic, sonn- on tlie I'aciHe, and some on both slopes. On the other liaii 

 TIii/iiikUus has a laruer number of dorsal rays than any racilie slope species. 



The clianj-e fiom rays to s])ines is seen in Arrhoplitcx. Molo, etc. It is inn- 

 •strikinjjly marked in tiie chan.t>'e from Pircopnis to Vithimhia, the only known j>eiic; 

 of t'.ie l*rrcnps(ibv. The former is conlined to tlie Atlantic;, the latter to the Parii 

 slope. In tiie former, feelde unse<>,ineuted rays at the besinninji of th«' dorsal and 

 the anal are deveiopi'il inti) stron.i;- sjiines in the latter. Long ago Prof. Cojii 

 noficed a similar m (litication as to sjjines in Mvda. I'rof. Cojie says: 



As ciiii! of till' iii'ist valiiiible results derivcil froiii ;i .study ot" tlie i-ollectioiis, it jiiipear.s tli:it i 

 ba.siii l)f■tllt^ Coloriiili) Uivcr is tins liiibitiit of ii isinall j;rou|> of lislics of tlie fauiily ^'upriiiidii; which in 

 lie (mIIi'iI tlir I't.ttiophnn r. wliicli eiiibiM^cs tlircc jri-iici-ii — /'/<(r/(>y(/c(».'( Cope, l.i'indomvihi ('op*', iind .1/ 

 Giriird. The ni'oup dillVrs IVdmi others oi tiie I'uinily in the ))osscssioii of two stron;; osseous i:iy- 

 tliedi)rsMl (in, tlii', pistcriar of wliicli is let into !i groove in the hinder lace of the anterior wiilii 

 lieiiij; coiissilicil with it, tiiiis coustitutinj; a coiiipoiiiid defensive Kj)ine. The rays of the veiiti;il: 

 ^xce|)tinij till' first anil sfiDUil. are siiuilarl,\ iiiodilied. The greater jiart of tiieir length eoiisisl. 

 an osseous dagiicr-shain'il spine, with ,nioo\ cd postericu' cd!;e, which overlaps the border of the suicr 

 inif ray, Avlicii the tiu, like a fan, is closed up. Tlie arliiMilated jiorlion of the ray either einer<>cs li 

 the groove below the fren acute ajjcx of the spine, or a|)]»cars ;is a coiitinuation of the apt^x it- 

 * ' ■" IntiU'est attaclu^s to the I'Ui'iHjitiriniv as the only typ(! of lishes not known from other wiii- 

 than those of the Colorado and Sail Luis basins. 



An interesting i-ondition is .seen in llystrrinaipm, tlie only fresh water gemi> 

 the I'Jinhiotorithv. It is conlined to the Sacramento IJasin and has Hi to 18 dorsal spin 

 as compared with 8 to 11 in the many marine geneni, rnfortunately this is the m 

 available e.\ami)le of the chiiiige from salt to fresh water. 



I give here a detailed comparison of the rays of the I'acilic tishes as coiiij 

 with their Atlantic relatives, from which it will be seen, as stated above, that in c\ 

 family the modification is noticeable, although in many cases it is minute. As tli 

 possible the western iind eastern representatives of the same forms are placed oppn 

 to each other. 



ACIPKNSKUIU.K. 



iiii 



Species 



Acipi'ii.si'i' IrJiiisinoQtiiiiiis. . 

 Aci|M'ii.sci' iiicilii'Dsti'i.v 



* Cope & Yarrow, Wheeler's Surveys, chapter vi, Report upon the Collections of Fishes iii. 

 in p')rtion9 of Nevada, Utah, California. Colorado, New Mexico, aiid Arizona. 



^j^^Hj; I 



