OYPRINID^ OF EASTERN CANADA. 41 



to permit of the group being divided into two species, though 

 an extreme may deserve recognition as a variety. 



To the relative height, too, of the dorsal and the form of its 

 free margin is attached some significance in the attempted se'p- 

 aration of dissmtVis from ^;/M77^6e»s, the former having the mar- 

 gin nearly straight with anterior rays not produced, the latter 

 with the margin concave and rays produced. When somewhat 

 marked, constant, and associated with other contrasts, the fea- 

 lure would be of some value ; otherwise it should be used with 

 much caution, for it is just in these two respects that fins of the 

 same species are often found to difier. Age, sex, season, and na- 

 ture of summer and winter habitats are modifying causes. Ana- 

 dromous tribes, and fishes of lacustrine habit, resorting to the 

 upper courses of rivers for breeding purposes, exhibit at dif- 

 ferent seasons a considerable variation in this respect. Our At- 

 lantic salmon is a good example. Under these circumstances 

 there is extra wear or abrasion of the anterior rays and external 

 parts, often materially changing the outline. Ceratichthys ex- 

 hibits all these modifications; but the shortened anterior rays and 

 straight or convex margin of the dorsal are, as a rule, associated 

 with the maximum, scale Jormida in the isolated colony referred to. 

 The shape, size, and profile of the head and degree of con- 

 vexity of outline anterior to th*^ dorsal fin vary much. Indeed, 

 within the range described, plumheus seems to include the three 

 forms noted above, and it would, therefore, appear more scien- 

 tific to regard them as varieties of one widely dispersed species. 

 In "Fishes of North and Middle America," by David Starr Jor- 

 dan, Ph. D., and Barton W. Evermann, Ph. D., Washington, 

 1896, the learned authors are disposed to recognise the specific 

 identity of plumbeus and dissimilis. There are equally good 

 reasons for including greeni as well. 



6. C. plumbeus Agassiz. 



Generally distributed over eastern Canada : not found on P. 

 E. Island. Not uncommon in Ontario (Macoun). 



