percopsid.'e — the rrout-perches 225 



Family PERCOPSIDjE 



(the trout-perches) 



Body moderately elongate, somewhat compressed; caudal peduncle 

 rather long and slender; scales with edges strongly ctenoid; head naked; 

 lateral line developed; skeleton bonv; anterior vertebrae simple; ventral 

 fins abdominal, somewhat anterior; dorsal fin with 2 spines; ventrals 

 with 1 rudimentary spine and about S rays; anal with 1 or 2 spines; 

 caudal forked; an adipose fin present; no mesocoracoid ; gill-membranes 

 separate, free from isthmus; branchiostegals 6; pseudobranchia? pres- 

 ent; gill-rakers short, tubercle-like; opercle with entire edges; mouth 

 small, horizontal; premaxillaries not protractile; teeth very small, villi- 

 form, on premaxillaries and lower jaw only; stomach siphonal, with 

 about 10 well-developed pyloric caeca; air-bladder present, with an open 

 duct I Boulenger) ; ova large, not falling into the abdominal cavitv before 

 extrusion. 



Small fishes of the fresb waters of North America ; 2 genera 

 known, each containing a single species ; one species found in Illini >is. 



This family "shows the remarkable combination of true fin- 

 spines, ctenoid scales, and a percoid mouth, with the adipose fin, 

 abdominal ventrals, and naked head of the Isospondyli" (herring- 

 like forms). It is doubtless a surviving remnant of a fauna which 

 marked the transition from the soft-rayed herring-like forms to the 

 later-appearing groups of aeanthoptervgian fishes. 



Genus PERCOPSIS Agassiz 



(trout-perch ) 



Characters in the mam as above, differing from the single other 

 known genus of the family (Columbia Eigenmann, recently described 

 from the Pacific slope) in the weaker dorsal spines, the more translucent 

 body, and the relative absence of serration of the preopercle. Atlantic 

 slope and Great Lake region, in clear cold waters; one species 



PERCOPSIS GUTTATUS Agassiz 



(trout-perch) 



Agassiz, 1850, Lake Superior, l*t< 



G.. VI. 207; J. & G , .<2 2; M V., 82; J. & E., I, 7S4; X., 4.?; J., 53; F.. 72; L . 12. 



Length 6 inches; body elongate, nol much compressed, strongly 

 tapered posteriorly, tin- caudal peduncle slender; depth 3 . ( > to 4.5; 

 greatesl width § greatest depth; deptli caudal peduncle 2 . 7 to 3.2 m its 



