76 (^HECK LTRT OF THE 



Family PERCOPSID.^. (Trout Perches.) 



Body moderately elongate, somewhat compressed, the caudal peduncle 

 long and slender. Head conical, pointed, naked. Mouth small, hori- 

 zontal ; maxillary short, narrow, without supplemental bone, not reaching 

 to the large eye; margin of upper jaw formed by premaxillaries alone, 

 which are short and not protractile. Teeth very small, villiform on pre- 

 maxillaries and lower jaw only. Tongue short, adherent. Gill membranes 

 separate ; free from the isthmus. Pseudobranchia? present. Branchio- 

 stegals six. Gill rakers short, tubercle-like. Opercle with entire edges. 

 Lower limb of the preopercle well developed, the angle nearly a right 

 angle, its inner edge with a raised crest, its outer edge crenulate or with 

 a few spines. Bones of the head cavernous; cranium with a raised crest, 

 which does not extend to the occiput. Scales moderate, rather firm, adher- 

 ent, their edges strongly ctenoid. Lateral line continuous. Dorsal short, 

 median with two spines, slender or stout; ventrals anterior, just in front 

 of the dorsal, with one rudimentary spine and about eight rays; pectorals 

 narrow, placed rather high; anal small, with one or two spines; caudal 

 forked ; adipose fin present, small. Vertebrae about thirty-five. First 

 superior pharyngobranchial without teeth ; second, third, and fourth separ- 

 ate, with teeth. Lower pharyngeals separate. Stomach siphonal, with 

 about ten well developed pyloric caeca. Ova unusually large, not falling 

 into the abdominal cavity before exclusion. Air bladder present, with a 

 band of connective tissue which is apparently with a rudimentary duct. 

 Small fishes of the fresh waters of the cooler parts of America. This group 

 is one of special interest, as it combines with ordinary salmonoid charac- 

 ters, the structure of the head and mouth of a Percoid. 



Genus PERCOPSIS. (Trout Perches.) 



Body rather slender, pellucid, covered with rather thin scales; dorsal 

 fin with two slender spines or simple rays ; anal with one ; scales roughest 

 posteriorly; lateral line developed; preopercle entire or very nearly so. 



(82) Trout Perch. Sand Roller. 



(Percopsis guttatus.) 



Body rather long, moderately compressed, covered with thin ctenoid 

 scales ; head scaleless and without barbels ; gill openings wide ; opercles 

 well developed ; gill rakers short, tubercular ; skull highly cavernous ; 

 mouth small, the margin of the upper jaw formed by the short non-pro- 

 tractile intermaxillarics ; no sujjplemental maxillary bone; small villiform 



