PISHES OP THE FAMILY LORICARIIM. 237 



Length of mandibular ramus about 3| times in the interorbital width. Snout broad, 

 rounded ; supraorbital edges not raised ; supraoccipital flat ; temporal plates not 

 carinate. Scutes spinulose, not carinate, 22-23 in a longitudinal series, 5-6 between 

 dorsal and adipose fin, 9 between anal and caudal. Supraoccipital bordered posteriorly 

 by a median scute and by one on each side. Lower surface of head and abdomen 

 naked. D. I 7, the first ray f- the length of head, the last f as long, joined by a 

 membrane to the adipose fin ; length of base of dorsal greater than its distance from 

 the caudal. A. I 4. Pectoral spine stout, bristly, extending to base (young) or 

 anterior -g- (adult) of ventral. Caudal obliquely truncate. Caudal peduncle about 

 1-g- times as long as deep. 



Total length 240 mm. 



Three specimens (types of the species, of II. nigricans and II. vicinus respectively) : 

 Peruvian Amazon. 



The largest specimen is stuffed and is orange-red in colour; the two smaller ones 

 in spirit are blackish. The one named H. vicinus has the spine of the adipose fin 

 small, recumbent, and immovably joined to the scute below it. 



22. Ancistrus heteracanthus. 



Cheetostomus heteracanthus Giiath. Proc. Zool. Soc. 1869, p. 425, figs. 3 & 4. 

 Hemiancistrus heteracanthus Eigenm. & Eigenm. Proc. Cal. Ac. (2) ii. 1889, p. 44. 



Depth of body 5-g- times in the total length, length of head 2f times. Head 1-^ 

 times as long as broad and twice as long as deep. Diameter of eye 8f times in the 

 length of head, interorbital width 1^ times, length of snout If- times. Length of 

 mandibular ramus 4 times in the interorbital width. Snout margined with very short 

 bristles ; supraorbital edges not raised ; supraoccipital flat ; temporal plates not 

 carinate; interoperculum armed with 12 stout spines, the longest equal to a little 

 more than \ the length of head ; external to these, and overlying them, some long 

 slender bristles. Scutes spinulose, not carinate, 24 in a longitudinal series, 7 between 

 dorsal and adipose fin, 12 between anal and caudal. Supraoccipital bordered 

 posteriorly by a median scute and by one on each side. Lower surface of head 

 naked ; abdomen with some small scattered granules. D. 1 7, the first ray equal to 

 f the length of head, the last f as long ; length of base of dorsal nearly equal to its 

 distance from the adipose fin. A. I 5. Pectoral spiue extending to beyond middle of 

 ventral. Caudal peduncle 2-f times as long as deep. Olivaceous ; a blackish spot at 

 the base of the first dorsal ray. 



Total length ISO mm. 



One specimen: Peruvian Amazon. 



23. Ancistrus rictus. 



Hypostomus piclus Casteln. Anim. Am. Sud, p. 44, pi. xxii. fig. 2 (1855). 



Depth of body about 6 times in the total length, length of head 2f times. Head 



