45^ Memoir Sears Foundation for Marine Research 



being represented by a fold of the peritoneum. Stomach with Pyloric caeca except in 

 Salangidae. 



Remarks. For discussion of the characters that distinguish the Salmonoidea from 

 other Suborders of the Isospondyli, see Key to Suborders (p. 95) and related text. 



Families. Of the six families recognized in the following Key, three are represented 

 with detailed accounts in this series: Salmonidae (p. 457), Coregonidae (p. 547), and 

 Osmeridae (p. 553). The Thymallidae (graylings), Plecoglossidae (ayu or sweetfishes), 

 and Salangidae (icefishes) occur in northern waters of western North America, Europe, 

 Siberia, northern China, Korea, and Japan. Many of the species are anadromous, as- 

 cending freshwater rivers to spawn. 



Key to Families 



I a. A fleshy axillary lobe on each side close above base of pelvic fins. 

 2 a. Rayed dorsal fin, when depressed, shorter than head. 



3a. Teeth well developed on jaws, on roof of mouth, and on tongue; at least 

 19 scales in a transverse series from origin of dorsal fin to lateral line; 

 parietal bones of skull not meeting in the midline. Salmonidae, p. 457. 

 3b. Teeth minute or lacking; not more than 13 scales in a transverse series 

 from origin of dorsal fin to lateral line; parietal bones of skull meeting 

 in the midline. Coregonidae, p. 547. 



2 b. Rayed dorsal fin, when depressed, much longer than head. 



Thymallidae. 



Mostly in clear, cold streams, seldom 

 entering salt water; western North 

 America, northern Europe, and Siberia. 

 I b. No axillary lobe above base of pelvic fins. 



4 a. Head only slightly depressed, its depth at eyes 67 "/o or more of body depth 

 at dorsal fin; snout in front of eyes at least no longer than base of dorsal fin; 

 body not transparent; branchiostegal rays 6-10; swim bladder present; 

 stomach with pyloric caeca. 



5a. Jaw teeth firmly and directly attached to jaw bones; tongue not pleated; 

 not more than 10-12 pyloric caeca. Osmeridae, p. 553. 



5 b. Jaw teeth arranged on serrated plates on inner sides of jaws, not directly 

 attached to jaw bones; tongue pleated; up to 400 pyloric caeca. 



Plecoglossidae.^ 



Running up cold streams to spawn; 



coastal waters of Japan and Formosa. 



4 b. Head strongly depressed, its depth at eyes less than 50 "/o of body depth at 



dorsal fin ; snout in front of eyes about twice the length of base of dorsal fin ; 



body transparent; branchiostegal rays only 3 or 4; no swim bladder; no 



pyloric caeca. Salangidae.* 



Ascending rivers to spawn; coastal waters 

 of Japan, Korea, and northern China. 



3. Only known genus, Plecoglossus. 4. Contains only one genus, Salanx. 



