FISHES OF THE MISSOURI RIVER BASIN. 



411 



central part of the region examined. It appears to be common, however, in 

 certain Wyoming streams. The finest, largest, individuals obtained are those 

 from Rapid Creek and Tongue River, the largest of these measuring about 6 

 inches in total length. Head 4£ to 4* ; depth 4 to 5 ; eye 4 to 5 ; snout 3 to 4 ; 

 D. 8* A. 8. There is considerable variation in the scales, the extremes 

 being 12-72-8 and 12-64-8, the usual number, however, being 12-68-8. 

 Occasionally there are 11 to 13 scales above (and including) the lateral line. 

 In the fifth edition of Jordan's Manual of Vertebrates, Couesius dissimilis 

 is distinguished from C. plumbeus as having fewer scales in the lateral line, 

 the number given for dissimilis being 60 and for plumbeus 68. This is evidently 

 a mistake. Specimens in the National Museum of what have been called 

 plumbeus, from Lake Superior and the Adirondacks, have 70 to 75 scales in 

 the lateral line. This is not sufficiently different from western specimens to 

 be of any specific value. While we can not see how these species can be dis- 

 tinguished by the scales, we think we have discovered a character which 

 will serve to distinguish them, viz: The differences in the dorsal and anal 

 fins, which may be stated thus : 



a. Height of dorsal fin 1 to 1$ in head, free margin of fin concave, the anterior 

 rays produced and extending beyond the others when the fin is depressed. 

 Length of longest anal ray if to 1-J- in head, the free margin of the tin more 

 or less concave, the anterior rays somewhat produced, and when deflexed 

 extending slightly beyond other rays plum beus. 



an. Height of dorsal 1 $ to li in head ; free margin of fin nearly straight, the 

 anterior rays little if at all produced, and when depressed barely reaching 

 beyond end of other rays. Length of longest anal ray If in head, free mar- 

 gin of fin straight, anterior rays not produced and not extending beyond end 



of others when depressed dissimilis. 



These differences are well marked between the specimens of dissimilis 

 examined and all specimens of plumbeus from the upper Great Lakes region. 

 A specimen (U. S. N. M., No. 34388) collected in the Adirondacks by Mr. Fred 

 Mather, seems to belong to Couesius plumbeus, though it does not wholly 

 agree with those from Lake Superior. The height of the dorsal fin is 1£ in 

 head, the anterior rays are somewhat produced and extend some beyond the 

 other rays when the fin is depressed ; the free margin is but slightly con- 

 cave. The longest anal rays are contained If times in length of head, the 

 anterior rays are but little produced and do not reach beyond the others 

 when dellexed; the free margin of the anal fin is nearly straight. The origin 

 of the dorsal fin is midway between middle of pupil aud base of caudal. This 

 posterior position of the dorsal is a character, however, not possessed by the 

 other specimens of C. plumbeus examined. This species differs from C. greeni 

 of the Columbia and Frazer River basins in the smaller scales and in having 

 the scales more crowded on the anterior part of the body. There is consid- 

 erable variation in the squamation of this species, however. Examination 

 often examples from Sheridan gives the following results: 



