234 ME. 0. TATE REGAN OS THE 



broad as long and 2? times as long as deep. Diameter of eye 4§- 5| times in the 

 length of head, interorbital width 2f times, length of snont If times. Length of 

 mandibular ramus 2-g- times in the interorbital width. Snout broad, rounded ; supra- 

 orbital edges not raised; sn preoccipital flat, without median ridge; temporal plates 

 not carinate; interoperculum armed with 20-25 slender spines with curved tips, the 

 longest equal to twice the diameter of eye. Scutes spinulose, not carinate, 25 in a 

 longitudinal 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). D. 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. 



Two specimens : British Guiana. 



17. A5CISTRUS MEGACEPHALUS. 

 ? Hypostomus itacua Cuv. & Val. Hist. Nat. Poiss. xv. p. 505 (1840) ; Val. Voy. d'Orbigny, Poiss. 



pi. vii. fig. 1 (1847). 

 ? Chcetostomus itacua Giinth. Cat. Fish. v. p. 243 (1861). 

 Chcetostomus megacephalus Giinth. Proc. Zool. Soc. 1868, p. 232. 

 Chcetostomus macrops Liitk. Vid. Medd. 1873, p. 209; Steirid. Denksclir. Ak. Wien, xliii. 1881, 



. p. 125, pi. v. fig. 3. 

 ? Hemiancistrus itacua Eigenm. & Eigenm. Proc. Cal. Ac. (2) ii. 1889, p. 43 ; Kindle, Aim. Ac. 



N. York, viii. 1895, p. 253. 

 Hemiancistrus megacephalus Eigenm. & Eigenm. t. c. p. 4-1; Kindle, 1. c. 



Depth of body 4-4^ times in the total length, length of head 2f times. Head 1^ 

 times as long as broad and lf-lf times as long as deep. Diameter of eye 5-5^- times 

 in the length of head, interorbital width 3^ times, length of snout l-§— If- times. 

 Length of mandibular ramus If times in the interorbital width. Snout rounded 

 anteriorly ; supraorbital margins raised ; supraoccipital fiat, without median ridge ; 

 temporal plates not carinate ; interoperculum armed with 30 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. I 7, the first ray f the length of head, the last f as long ; length of base of dorsal 

 nearly equal to its distance from the caudal. A. I 4. Pectoral spine extending to 

 well beyond base of ventral. Caudal weakly and obliquely emarginate. Caudal 

 peduncle 2\ times as long as deep. Lach scute on the body with a large light spot, 

 similar smaller spots on the head. Fins with bluish cross-bands. 



Total length 175 mm. 



