82 TELEOSTEI: HAPLOMI. XIV. 



FAMILY XXXV. PERCOPSID^J. (THE 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 Ericymba; fins much 

 as in Salmonidce ; pellucid ; branchiostegals 6 ; stomach siphonal 

 with about 10 pyloric caeca; 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 Salmonidce, but 

 having the mouth and scales decidedly Perch-like. 



84. PERCOPSIS Agassiz. (ire/oKi;, perch ; fyis, appearance.) 



195. P. guttatus Agassiz. TROUT PERCH. Silvery; upper 

 parts with rounded dark spots made up of minute dots ; lower jaw 

 included; tail long. Head 3f ; depth 4^. 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.) 



ORDER XIV. HAPLOMI. (THE PIKE-LIKE FISHES.) 



This order differs from the other soft-rayed fishes, chiefly in the 

 simpler structure of the shoulder girdle, which lacks the prsecoracoid 

 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 pseudobranchiae are wanting or glandular. The group is made 

 up chiefly of fresh-water species. (&7r\6os, simple; &/*os, shoulder.) 



FAMILY XXXVI. AMBLYOPSID^E (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 csecal, 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. 



