250 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



Of this species 62 specimens, ranging from 30 to 260 mm. in length, 

 were preserved. It is common in the Rio Tuyra Basin, but only a few 

 specimens were obtained in the Rio Bayano and a single specimen in the 

 Rio Chagres. The last was speared at night by torch light by a native 

 at Alhajuela. 



This species lives among the rocks, apparently prefering the rapid 

 courses of streams. In clear water it may often be seen huddled close 

 to the rocks to which it is able to attach itself by means of its sucking 

 mouth and flat ventral surface. It feeds on algae and other plants. Its 

 alimentary canal is convoluted and many times the length of the body. 

 It is prepared as food by the natives of Darien, by boiling it in water. 



Habitat: Both slopes of Panama. 



8. Genus Ancistrus Kner. 



Ancistrus Kner, Denkschr. K. Ak. Wiss. Wien, VII, 1853, 272 (sp.); 



Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 77 (type Hypostomus 



cirrhosus Cuvier & Valenciennes). 

 Thysanocara Regan, Ann. & Mag. Nat. Hist., Ser. 7, XVII, 1906, 95 



(type Hypostomus cirrhosus Cuvier & Valenciennes). 



Body anteriorly broad; caudal peduncle posteriorly compressed; 

 margin of snout naked, bearing tentacles; the naked margin broad in 

 males and with many tentacles, narrow in the females and with few 

 short tentacles; preopercle independently movable, bearing spines; the 

 premaxillaries and dentaries of about equal length, the mandibular 

 ramus much narrower than interorbital; plates on head and scutes on 

 body without prominent ridges or carinations; adipose fin well developed. 



KEY TO THE SPECIES. 



a. Fins moderately elevated, the posterior rays of the dorsal failing 

 to reach adipose when deflexed; base of dorsal scarcely equal to 

 the distance from the base of the last ray to the tip of the spine of 

 the adipose; pectoral fins failing to reach the middle of the 

 ventrals, the spine notably shorter than the head; second scute 

 behind occipital without a distinct median suture. 



chagresi, p. 251. 



aa. Fins strongly elevated, the posterior rays of dorsal reaching past 

 origin of adipose when deflexed; base of dorsal equal to the 

 distance from the base of the last ray to the base of caudal; 

 pectoral fins reaching to or past the middle of ventrals, the spine 

 longer than head; second scute behind occipital with an evident 

 median suture. spinosus sp. nov., p. 252. 



