270 FISHES. 



SUB-OEDER ISOSPOKDTLL 



(The Trout-like Fishes.) 



FAMILY CIV. PERCOPSID^E. 



(The Trout Perches) 



Body covered with moderate-sized ctenoid scales; head 

 naked; no barbels; opercles well developed; gill open- 

 ings wide; an adipose fin; jaws with villiform teeth; no 

 teeth on voiner or palate; margin of upper jaw formed 

 by intermaxillaries alone; branchiostegals six. A single 

 genus and one or two species inhabiting the fresh waters 

 of the northern U. S. Interesting little fishes, with the 

 general characters of SalmonidoB^ but having the mouth 

 and scales decidedly Perch-like. 



/. PERCOPSIS, Agassiz. TROUT PERCHES. 

 1. P. guttatus, Ag. Depth 4 in length; head 3f; 

 silvery, almost pellucid; upper parts with rounded dark 

 spots made up of minute dots; I). 11; A. 7; L. 10; 

 Great Lakes; Ohio B. (Jordan); Potomac R. (Baird); 

 Delaware R. (Abbott.) 



FAMILY CV.-SALMONID^E. 



(The Trout.) 



Head naked, body scaly, 110 barbels; margin of upper 

 jaw formed by intermaxillaries mesially and by maxil- 

 laries laterally; adipose fin present; belly rounded; air- 

 bladder large, simple; pseudobranchias present; pylori c 

 appendages usually numerous; eggs falling into the 

 cavity of the abdomen before exclusion. Fresh waters 

 of northern regions, many species periodically descend- 

 ing to the sea; a few permanently marine. 



Genera sixteen; species one hundred and sixty. The 



