PERCOPSID^: THE TROUT-PERCHES 225 



FAMILY PERCOPSID^ 



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 bony; anterior vertebrae simple; ventral fins 

 abdominal, somewhat anterior; dorsal fin with 2 spines; ventrals with 1 

 rudimentary spine and about 8 rays; anal with 1 or 2 spines; caudal forked; 

 an adipose fin present; no mesocoracoid ; gill-membranes separate, free from 

 isthmus; branchiostegals 6; pseudobranchise present; gill-rakers short, 

 tubercle-like; opercle with entire edges; mouth small, horizontal; premaxil- 

 laries not protractile; teeth very small, villiform, on premaxillaries and 

 lower jaw only; stomach siphonal, with about 10 well-developed pyloric 

 caeca; air-bladder present; with an open duct (Boulenger); ova large, not 

 falling into the abdominal cavity before extrusion. 



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

 known, each containing a single species; one species found in 

 Illinois. 



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 acanthopterygian fishes. 



GENUS PERCOPSIS AGASSIZ 



TROUT-PERCH 



Characters in the main 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 



(MAP LXVII) 



Agassiz, 1850, Lake Superior, 286. 



G., VI, 207; J. & G., 322; M. V., 82; J. & E., I, 784; N., 43; J., 53; F., 72; L,., 22. 



Length 6 inches; body elongate, not much compressed, strongly tapered 

 posteriorly, the caudal peduncle slender; depth 3.9 to 4.5; greatest width % 

 greatest depth; depth caudal peduncle 2.7 to 3.2 in its length. Color of upper 



