216 FISHES. 



Most of them prefer clear running water, where they 

 lie on the bottom concealed under stones, darting when 

 frightened or hungry with great velocity for a short 

 distance by a powerful movement of the fan -shaped 

 pectorals, then stopping as suddenly. They rarely use 

 the caudal fin in swimming, and they are never seen 

 moving or floating freely in the water like most fishes. 

 When at rest they support themselves on their extended 

 ventrals and anal. Pleurolepis, unlike the others, pre- 

 fers a sandy bottom, where, by an almost instantaneous 

 plunge, it buries itself in the sand and remains quiescent 

 for hours at a time, with only its eyes and snout visible. 

 All are carnivorous, and, in their way, voracious. All 

 are of small size, the largest (Pertina) reaches a length 

 of about eight inches, while the smallest (Micropercci), 

 which is the smallest spiny -rayed fish known, barely 

 attains a length of an inch and a half. 



* Lateral line complete; body much elongate, subcylindrical, 



pellucid, with at least the entire ventral region naked. 

 a. Body entirely naked, except the caudal peduncle and the 

 lateral line ; dorsal fins high, well separated, equal to the 

 anal fin and to each other ; a single anal spine ; head en- 

 tirely scaleless; mouth large, with voinerine teeth, the 

 upper jaw subprotractile. . . AMMOCRYPTA, 1. 

 aa. Body covered above with small, thin, imbedded scales, the 

 ventral region entirely naked, the dorsal scales obscure but 

 present; dorsal fins small, wide apart; one anal spine ; 

 cheeks and opercles scaly; mouth large, with vomerine 

 teeth, the upper jaw subprotractile. . PLEUROLEPIS, 2. 

 ** Lateral line complete; body less elongate, entirely scaly, or 



with definitely naked areas on throat, neck, or ventral line. 

 f Second dorsal not larger than spinous dorsal, and little, if any, 

 larger than anal ; the dorsal fins distinct, the first the longer 

 and usually the larger ; body little compressed ; two dis- 

 tinct anal spines (except in Alwrdius peltatus, a species of 

 uncertain affinities). 



