322 COXTKIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 
Family XLVIL— PERCOPSID.E. 
{The Trout Perches.) 
Body moderately elongate, somewliat eompressed, the caudal pedun- 
cle long and slender. Head conical, pointed, naked. Mouth small, 
horizontal; maxillary short, narrow, without supplemental bone, not 
reaching to the large eye; margin of upi^er jaw formed by premaxilla- 
ries alone, which are short and not protractile. Teeth very small, villi- 
form on premaxillaries and lower jaw only. Tongue short, adherent. 
Gill-membranes separate, free from the isthmus. Pseud obranchice pres- 
ent. Brajiehiostegals 0. Gill-rakers short, tubercle-like. Opercle with 
entire edges. Lower limb of the i)reopercle well developed, the angle 
nearly a right angle, its inner edge with a raised crest. Bones of the 
head cavernous, as in Acerina and Ericyinba. Cranium with a raised 
crest, which does not extend to the occii)ut. Scales moderate, rather 
thin, adherent, their edges strongly ctenoid. Lateral line continuous. 
Dorsal short, median; ventrals anterior, just in front of the dorsal, 
8-rayed ; pectorals narrow, jilaced rather higher than usual ; anal 
small; caudal forked; adipose fin present, small. Stomach siphonal, 
with about 10 well -developed pyloric cceca. Ova rather large, not fall- 
ing into the abdominal cavity before exclusion. Air-bladder present. 
Small fishes of the fresh waters of the cooler parts of America; a sin- 
gle genus, with probably but one species. The group is one of special 
interest, as it combines with ordinary Salmonoid characters the structure 
of the head and mouth of a Percoid, resembling notably the European 
genus Acerina. 
{Percopsidee Gunther, \-i, 207.) 
152.— PERCOPSIS Agassiz. 
Trout Perch. 
(Agassiz, Lake Superior, 1850, 284: type Percopsis guttatus Ag.) 
Characters of the genus included above. perch; oYu?, appear- 
ance.) 
519. P. giitlJif MS Agassiz. 
Pale olivaceous, a silvery stripe along the lateral line, becoming ob- 
solete forwards ; upper parts with obscure round dusky spots made of 
dark points. Head slender and conical. Mouth small, subinferior, 
maxillary not nearly reaching front of orbit. Caudal peduncle long and 
