262 MR, C. TATE REGAN ON THE 
lower lateral series are below the temporal plate and in contact with it superiorly. As 
in the preceding genus, the head and body are rough and spinate and the scutes of the 
nuchal region are small and numerous. ‘The dorsal originates above the ventrals. 
‘There is no adipose fin. 
R. Amazon. 
ACANTHICUS HYSTRIX. 
Acanthicus hystrix Spix, Gen. et Spec. Pisce. Bras. p. 3, pl. i. (1829) ; Schomburgk, Fish. Brit. 
Guiana, i. p. 131, pl. i. (1841) ; Giinth. Cat. Fish. v. p. 253 (1864), and Proc. Zool. Soc. 1868, 
p. 233; Eigenm. & Eigenm. Proc. Cal. Ac. (ii) 2, 1889, p. 46, and Oce. Papers Cal. Ac. i. 
1890, p. 440. 
Rinelepis acanthicus Cuv. & Val. Hist. Nat. Poiss. xv. p. 487 (1840). 
Depth of body 53 times in the total length, length of head 23 times. Breadth of 
head 12 times in its length, diameter of eye 16 times, interorbital width 53 times, 
length of snout twice. Head nearly flat above; snout spiny: supraoccipital and 
temporal plates with radiating spinate lines; interoperculum armed with numerous 
slender spines, the longest 5 times in the length of head. Scutes with strong spiny 
keels, 25 in a longitudinal series; nuchal scutes smail and numerous. Lower surface 
of head and abdomen completely covered with small granular scales. D.1 7; length 
of base of dorsal equal to 4 the distance from the caudal, A.1I5. Pectoral spine 
extending to posterior 4 of ventral; caudal emarginate, the outer rays produced. 
Caudal peduncle 43 times as long as deep. Brownish; fins with dark spots or bars. 
Total length 450 mm. 
One specimen: R. Amazon; Guiana. 
Subfamily Il. HypPopTopoMATIN &. 
Vertebree below the dorsal fin with bifid neural spines; none of the hemal spines 
bifid; pharyngeals not toothed; teeth in the jaws in a single series ; pseudobranchie 
present; upper part of the body enclosed in bony scutes, which form 5 longitudinal 
series anteriorly on each side of the compressed, cylindrical, or moderately depressed 
caudal peduncle, 3 posteriorly ; lower transverse part of clavicles and coracoids exposed, 
appearing as two pairs of plates between the bases of the pectorals ; margin of snout 
composed of more or less firm plates ; anterior rudimentary ray of ventral internal and 
directed forwards. 
Key to the Genera. 
Temporal plates imperforate. Eyes placed very low. . . . . ~ 9. Hypoptopoma Gthr. 
Temporal plates perforated likeasieve . . . - . . +. + + . 10 Otocinclus Cope. 
