82 TELEOSTEI : HAPLOMI. — XIV. 
Famity XXXV. PERCOPSIDA. (Tue Trout PERcHEs.) 
Body elongate, covered with moderate-sized, thin, strongly ctenoid 
scales; head naked; no barbels; opercles well developed ; gill open- 
ings wide; an adipose fin; mouth small, horizontal; teeth very 
small, villiform; no teeth on vomer or palate; margin of upper 
jaw formed by premaxillaries alone, these short and not protrac- 
tile; gill rakers tubercle-like; cavernous structure of the skull 
highly developed, as in Stelliferus, Acerina and Lricymba ; fins much 
as in Salmonide; pellucid; branchiostegals 6; stomach siphonal 
with about 10 pyloric ceca; ova large; no oviduct. A single spe- 
cies inhabiting cold fresh waters in the northern U.S. Interest- 
ing little fishes, with the general characters of Salmonide, but 
having the mouth and scales decidedly Perch-like. 
84. PERCOPSIS Agassiz. (mépkn, perch; dys, appearance.) 
195. P. guttatus Agassiz. Trout Percy. Silvery; upper 
parts with rounded dark spots made up of minute dots; lower jaw 
included; tail long. Head 33; depth 44. D. 11. A. 8. Lat. 1. 
50. L. 10. Great Lakes and tributaries, rarely S.; Ohio R. 
(Jordan); Potomac R. (Baird); Delaware R. (Abbott); Kansas 
(Gill). (Lat., spotted.) 
OrperR XIV. HAPLOMI. (Tue Pike-rixe FIsuHEs.) 
This order differs from the other soft-rayed fishes, chiefly in the 
simpler structure of the shoulder girdle, which lacks the preecoracoid 
arch. ‘There is never an adipose dorsal; the dorsal is posterior in 
position and the head is depressed and usually more or less scaly. 
The pseudobranchie are wanting or glandular. The group is made 
up chiefly of fresh-water species. (dmAocos, simple; dos, shoulder.) 
Famity XXXVI. AMBLYOPSIDA (THE Cave 
FIsHES.) 
Body elongate, with long depressed head; mouth large, the lower 
jaw projecting; premaxillaries scarcely protractile, forming whole 
edge of upper jaw; teeth villiform; eyes sometimes rudimentary 
and concealed under the skin; head naked, with papillary ridges; 
body with small, cycloid scales, irregularly arranged; no lateral 
line; D. far back, opposite A.; C. rounded; V. small, or wanting; 
vent at the throat, as in Aphredoderus; gill membranes joined to 
isthmus; stomach cecal, with pyloric appendages; some (and 
probably all) viviparous. Genera 3; species 5. 
Fishes of small size living in subterranean streams and ditches of 
the central and southern U. S., probably remnants of an ancient 
fauna. 
