ARGYROSOMUS — CISCOES 53 



Strong teeth, the two anterior ones curved backwards and sHghtly 

 inwards, and the posterior pair much smaller and directed almost 

 exactly inwards. These teeth disappear as the fish grows up, the 

 food changing likewise until, in the adult, it consists mainly of 

 small mollusks and crustaceans, with larvae of insects and other 

 animal forms. The gill-rakers of the adult are of a size and 

 number to enable it to separate from the water organisms as small 

 as Entomostraca, and where these are abundant they make a large 

 percentage of the 'food. The general character of the contents of 

 the stomach indicates, however, that the fish feeds habitually at 

 the bottom, as might indeed be inferred from the character of its 

 mouth. In aquaria it has been forced to feed on small fish in win- 

 ter, and has learned to pursue and seize its prey much as a trout 

 would do. 



It is caught mainly in gill- and pound-nets from April to the end 

 of December. It is not properly an angler's fish, although where 

 abundant it may be taken on the hook with a bait of worms or in- 

 sect larvffi. Fortunately for the future of the species, this valuable 

 and popular food-fish is one of those best adapted to artificial propa- 

 gation. Females are adult in three or four years, and 75 to 95 per 

 cent, of their eggs yield the young in the hatchery. 



A single other species of the genus Coregonus (C. quadrilateralis , 

 the round or Menominee whitefish) is taken in Lake Michigan, 

 though much more rarely than the common whitefish. A suffi- 

 cient characterization of this species will be found in the key to the 

 species of Coregonus preceding. 



Genus ARGYROSOMUS Agassiz 



(CISCOES) 



Close to Coregonus, from which it differs chiefly in the larger mouth 

 and more produced jaws, the premaxillaries being placed nearly horizon- 

 tally, and the lower jaw projecting decidedly beyond them; gill-rakers 

 very long and slender; dorsal fin of 9 to 12 rays; caudal forked; scales, 

 etc., as in Coregonus; vertebrae 55. Fresh waters of northern Europe, 

 Asia, and North America. Species numerous; about 6 known from the 

 Great Lake region of the United States. 



(5) 



