440 CALIFORNIA ACADEMY OF SCIENCES. 



DOUBTFUL SPECIES OF THIS GENUS. 



413.1. Hypostomus vicinus Castelnau, Anim. Ameri- 

 que du Sud, 45, pi. xxiii, fig. 1, 1855 (Ucayale). 



The figure represents this species as having a granu- 

 lar snout, a bundle of spines on the interopercle; no 

 adipose fin, dorsal adnate. If these characters are re- 

 liable vicinus is not an Acanthicus but a member of some 

 unnamed genus. 



ANALYSIS OF THE SPECIES OF ACANTHICUS. 



a. Entire head margined with spines; pectoral spine long and covered 

 with spines; scutes of the body isolate; caudal emarginate. 



hystrix 414. 



aa. Marginal spines restricted to the interopercular region; pectoral spine 

 short; scutes all contiguous or overlapping; caudal rounded. 



genibarbis 415. 



414, Acanthicus hystrix, 



Acanthicus hystrix Spix, Gen. et Spec. Pise. Bras. 3, pi. 1, 1829 

 (Amazon); Schomburgk, Fish. Brit. Guiana, part i, 131, pi. i, 

 1841 (Kio Branco); Giinther, v, 253, 1864 (copied); id. Proc. 

 Zool. Soc.Lond. 1868, 233(Xeberos); Eigenm. &Eigenm. Proc. 

 Cal. Acad. 2d Ser. ii, 46, 1889 (Para). 



Rine.lepis acanthicus Cuv. & Val. xv, 487 (copied). 



Habitat: Amazons from Para to Xeberos. 



This species seems to be very rare, but three speci- 

 mens being known. It is the roughest of the Plecos- 

 tomini which may partly account for its rarity in 

 museums. 



Depth If in the width, which is equal to length of 

 head to upper angle of gill-opening. Caudal peduncle 

 slender. Head broad, depressed, flat above, the surface 

 of the plates covered with short, conical spines, arranged 

 in radiating lines on the occipital and temporal plates; 

 margin of snout with numerous short spines. 



Orbit small, 8J in snout, 16 in head, 4J in the inter- 

 orbital. . 



Interopercle with numerous erectile spines, which are 

 flattened and curved at tip like the teeth of the mouth. 



