262 ME. C. TATE BEGAN 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 HYSTPJX. 



Acanthicus hystrix Spiv, Gen. ct Spec. Pise. Bras. p. 3, pi. i. (1829) ; Schombuvgk, Fish. Brit. 

 Guiana, i. p. 131, pi. i. (1841) ; Gimth. Cat. Fish. v. p. 253 (1864), and Proc. Zool. Soc. 1868, 

 p. 233 ; Eigenm. & Eigenm. Proc. Cal. Ac. (ii) 2, 1889, p. 46, and Occ. Papers Cal. Ac. i. 

 1890, p. 440. 



Rinelepis acanthicus Cuv. & Val. Hist. Nat. Poiss. xv. p. 487 (1840). 



Depth of body 5-f times in the total length, length of head 2f times. Breadth of 

 head If times in its length, diameter of eye 16 times, interorbital width 3f 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 small and numerous. Lower surface 

 of head and abdomen completely covered with small granular scales. D. 1 7 ; length 

 of base of dorsal equal to ^ the distance from the caudal. A. I 5. Pectoral spine 

 extending to posterior -g- of ventral; caudal emarginate, the outer rays produced. 

 Caudal peduncle 4-f times as long as deep. Brownish ; fins with dark spots or bars. 



Total length 450 mm. 



One specimen : R. Amazon ; Guiana. 



Subfamily II. Hipoptopomatixx 



Vertebra below the dorsal fin with bifid neural spines ; none of the haemal spines 

 bifid ; pharyngeals not toothed ; teeth in the jaws in a single series ; pseudobranchise 

 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 like a sieve 10. Otocinclus Cope. 



