87 

 Lkitiscis r>.\i/n:ATV? (Kkh.vrdson). A Sri dy in Vakiation.* ByCakj, H. 



J^IGENMANN. 



Nnwliorc I'Ise in North Aiiierioa do \vi' liiul witliin a liiuited region siicli ex- 

 U'usive variations among freshwater iislies as on tlie I'aciiic Slope. This is true 

 whether we have referenee to the extent of variation between tiie extremes of the 

 same lamilx" or to tiie limits of variation in any given species. 



A ooMii)arison of the members of tlie eight families of lishes having represen- 

 tatives on both the Atlantic and the Pacific slopes, show that, on an average, each 

 of thesi' families has ftnir genera and sixteen species on the Pacific slope, and 

 seven genera and thirty-six species on the Atlantic. Yet, although the numl)er 

 of species is more than twice as great on the Atlantic skipe, the variation in the 

 number of tin rays among tiie Pacific slope species is greater in all but two fami- 

 lies. I have recentlyt made a detailed comparison between the members of the 

 difTerent families, and there attributed this great extent of variation to two causes. 

 First: tlie fauna is of diverse origin ; some of the members are of Asiatic, while 

 others are ()f Atlantic descent. Second : the fauna is new as compared with the 

 Atlantic slope fauna, and has not yet reached a stage of staple equilibrium. It is 

 possible, as suggested to me by President .Jordan, that the Pacific slope fauna lias 

 retained its primitive characters more nearly than the Atlantic slope fauna, Avbich 

 shows signs of degeneration in its fins and teeth. 



This great variation between the members of the same families is not confined 

 to the tin rays. It is equally true of other characters, but can best be demon- 

 strated''in characters whose variation can be numerically expressed. The pharvn- 

 geal teeth of the Cyprinidie offer another striking example of these variations aniong^ 

 the Pacific slope species. In a number of cases the variations of the Pacific slope 

 species extend along dtfinite and parallel lines. I have pointed out some of these 

 in the paper quoted above. These lines are directed towards an increase of rays 

 and towards a modification of rays into spines. 



The following quotations from Gilbert and Evermann's recent work on the 

 Columbia River basin, j illustrate the variation among the different specimens of 

 the same species. " The range of variation seems to be very great, and ciiarac- 

 ters which are of undoubted specific value when applied to Atlantic drainage 



"Contriljutions from the Zoological Laboratory of the Indiana University, No. 11. 



tResults of explorations in Western Canada and Northwestern United States. BuIU 

 U. S. Fish Comm. for 1894, pp. 101 to 132, plates 5 to 8. June, 1894. 



t Report of the Commissioner of Fish and Fisherie.« on Investigations in the Ccilumbiii 

 River Basin in regard to the Salmon Fisheries. Washington, 1894. A Report upon Investi- 

 gations in ttie Columbia River Basin with Descriptions of Four New Species of Fishes. 



