45 8 Memoir Sears Foundation for Marine Research 



essentially freshwater fish, they apparently have never been able to spread through salt 

 water from one continent to another. Members of Salveltnus live the farthest north, 

 with S. alpinus ranging well within the Arctic Circle. [For the ranges of the species 

 discussed, see pp. 490, 499, 521, 539, and 543.] 



Figure 118. Outline of caudal fin : Sahelinus al- 

 pinus (left); Crist'womer namaycush (right). 



Figure 119. Outline of side of head: Salveltnus 

 alpinus (left), Brachymystax (right), illustrating dif- 

 ference in shape of lower margin of upper jaw 

 (maxillary bone). 



Key to Genera 



I a. Lower margin of sides of upper jaw (maxillary bones) weakly and uniformly 

 concave in outline (Fig. 1 19). 

 2 a. Anal fin usually with fewer than 13 rays. 



3 a. A double or zigzag series of teeth on shaft of vomer along midbelt of 

 roof of mouth, but sometimes lost in adult; sides with black markings. 



Salmo Linnaeus 1758, p. 459. 

 3 b. Teeth absent on shaft but present on head of vomer; sides without black 

 markings. 



4 a. Teeth on the vomer usually separated from the teeth on the pala- 

 tines. 



5 a. Caudal fin only moderately concave (Fig. 118); sides with red- 

 dish or salmon-colored spots; not more than 50 pyloric caeca. 



Salvelinus Richardson 1836, p. 503. 

 5 b. Caudal fin deeply concave (Fig. 118); sides with pale whitish 

 spots; about 140 pyloric caeca. 



Cristivomer Gill and Jordan 1878, p. 542. 

 4 b. Teeth on the vomer connected in an unbroken series with the teeth 

 on the palatines. Hucho Giinther i860. 



Rivers of central and eastern Europe, 

 northern Asia, and Japan. 

 2 b. Anal fin with 13-19 developed rays. Oncorhynchus Suckley 1861. 



Both sides of northern North Pacific.^ 



5. The Humpback Salmon {O.gorbuscha) has been introduced in several rivers of Maine and for a time it seemed that 

 it was established there, but it failed to maintain itself. The Silver Salmon {O.kisutch) also has been planted in Maine, 

 but without result. For further details see Bigelow and Schroeder {i8: 131-133). 



