234 MR. C. TATE REGAN ON THE 
broad as long and 23 times as long as deep. Diameter of eye 43-5} times in the 
length of head, interorbital width 23 times, length of snout 14 times. Length of 
mandibular ramus 24 times in the interorbital width. Snout broad, rounded ; supra- 
orbital edges not raised; supraoccipital flat, without median ridge; temporal plates 
not carinate; interoperculum armed with 20-25 slender spines with curyed tips, the 
longest equal to twice the diameter of eye. Scutes spinulose, not carinate, 25 in a 
Jongitudinal series, 6 between dorsal and adipose fin, 11-12 between anal and caudal. 
Supraoccipital bordered posteriorly by a median scute and by one on each side. 
Lower surface of head and abdomen naked (in the young). LD. I 7, the first ray } the 
length of head; length of base of dorsal nearly equal to its distance from the adipose 
fin. A. I 4. Pectoral spine not reaching the base of ventral. Caudal peduncle 
3 times as long as deep. Brownish, clouded with darker; dark spots on the fins. 
Total length 75 mm. 
‘lwo specimens: British Guiana. 
17. ANCISTRUS MEGACEPHALUS. 
? Hypostomus itacua Cuv. & Val. Hist. Nat. Poiss. xv. p. 505 (1840) ; Val. Voy. d’Orbigny, Poiss. 
pl. vii. fig. 1 (1847). 
? Chetostomus itacua Giinth, Cat. Fish. v. p. 243 (1864). 
Chetostomus megacephalus Giinth. Proc. Zool. Soc. 1868, p. 232. 
Chetostomus macrops Liitk. Vid. Medd. 1873, p. 209; Steind. Denkschr. Ak. Wien, xliii. 1881, 
p. 125, pl. v. fig. 3. 
? Hemiancistrus itacua Bigenm. & Eigenm. Proc. Cal. Ac. (2) ii, 1889, p. 43; Kindle, Ann. Ac. 
N. York, viii. 1895, p. 253. 
Hemiancistrus megacephalus Kigenm. & Higenm. t.c. p. 44; Kindle, 1. e. 
Depth of body 4-4} times in the total length, length of head 2} times. Head 14 
times as long as broad and 13-13 times as long as deep. Diameter of eye 5-5} times 
in the length of head, interorbital width 3} times, length of snout 15-12 times, 
Length of mandibular ramus I# times in the interorbital width. Snout rounded 
anteriorly ; supraorbital margins raised; supraoccipital flat, without median ridge ; 
temporal plates not carinate; interoperculum armed with 50 or more rather slender 
spines with curved tips, the inner longest and equal to 1} times the diameter of eye. 
Scutes margined, spinulose, not carinate, 24 in a longitudinal series, 7 between dorsal 
and adipose fin, 12 between anal and caudal. Supraoccipital margined posteriorly by 
a median scute and by one on each side. Lower surface of head and abdomen naked. 
D. 1 7, the first ray } the length of head, the last 3 as long; length of base of dorsal 
nearly equal to its distance from the caudal. A.I4. Pectoral spine extending to 
well beyond base of ventral. Caudal weakly and obliquely emarginate. Caudal 
peduncle 24 times as long as deep. Each scute on the body with a large light spot, 
similar smaller spots on the head. Fins with bluish cross-bands. 
Total length 175 mm, 
