56 CHECK LIST OF THE 



The Salmonidae are of comparatively recent evolution, none of them 

 occurring as fossils, unless it be in recent deposits. The instability of the 

 specific forms and the lack of sharply defined specific characters may be 

 in part attributed to their recent origin. 



Genus COREGONUS. (Whitekishes.) 



Body oblong or elongate, compressed ; head more or less conical, 

 compressed, the snout more or less projecting beyond the lower jaw ; mouth 

 small, the maxillary short, not extending beyond the orbit, with a well 

 developed supplemental bone ; teeth extremely minute, if present ; scales 

 moderate, thin, cycloid, rather firm. Dorsal fin moderate; caudal fin 

 deeply forked ; anal fin somewhat elongate ; ventrals well developed. 

 Pseudobranchiae large ; gill rakers varying from short and thickish to long 

 and slender ; air bladder very large ; vertebrae, fifty-six to sixty ; stomach 

 horseshoe-shaped, with about one hundred pyloric cseca ; ova small. 



Most of them spawn in late fall or winter near the shore, at other 

 seasons often frequenting considerable depths. 



The number of species of Coregonus has been overestimated and the 

 geographical range and range of variation of each one are much wider 

 than is generally supposed. 



All our species are highly valued as food and they probably constitute 

 the most important class commercially of our fresh water fish. 



Subgenus PROSOPIUM. 



(63) Frost-fish. Round Whitefish. 



(Coregonus quadrilateralis.) 



Body slender, elongate, subterete ; head long, the snout compressed 

 and bluntly pointed. Scales, 9-85-8. D. , 11; A., 10. 



Colour, upper parts dark bluish ; sides silvery. 



Length, about twelve inches ; it seldom attains much more than one 

 and a-half pounds in weight. 



The Frost-fish is abundant in the Great Lake region from the St. 

 Lawrence to Lake Superior and northward, and is everywhere highly 

 esteemed as a food fish. 



It spawns in October and November, visiting the shallow parts of 

 lakes and sandbars for that purpose. 



Subgenus COREGONUS. 



(64) Common Whitefish. 



(Coregonus clupeiformis.) 



Body deep, compressed ; back always more or less elevated, notably 

 so in the adult; caudal peduncle short; head small and short, the snout 

 blunt and obliquely truncated. Scales, 8-74 to 80-9. Dorsal, ten divided 

 rays ; anal, eleven divided rays. 



