286 PROCEEDINGS OF THE ACADEMY OF 



elevation, nuchal scuta not keeled. Orbits four times in head, 

 2.5 times in interorbital space. Muzzle regularly acuminate, a 

 triangular spot on extremity, smooth. Margins of muzzle not 

 spinous. Inferior surfaces rugose, except a smooth band sur- 

 rounding posterior lip, and a quadrate area within ventral fins. 

 Lip entire ; barbels short. 



Inferior caudal ray one-quarter longer than superior, no long 

 bristles on it or the ventral- 

 Total length 1.55 m. ; do. to dorsal fin .045 ; to anal ; hume- 

 ral width .07. Color yellow; below white, immaculate. Above 

 with three rows of ill-defined blackish spots at the unions of 

 scales, the inferior wanting behind the line of the dorsal fin. 

 Head above with many close brown dots. Dorsal fin with two 

 rows of blackish spots between each pair of rays ; one series be- 

 tween the caudals. Twenty-eight teeth on each ramus mandibuli. 

 From the Amazon, from Robert C. Perkins. This species is 

 especially distinguished by its short head, and by the characters 

 of squamation of lower surface, color, etc. 



PLECOSTOMUS SCOPULAKITJS, Cope, sp. nov. 

 Proc. Acad. Nat. Sci., Phila., 1871, p. 55. 



Is represented by a number of similar young individuals. 

 They differ in having a more slender muzzle, and dorsal radii II. 

 12, I. Ventrals also I. 5. 



CH.a;TOST0MTJS, Tsch. Heckel. 



There appear to be five nearly related species in the collection 

 from the Ambyiacu, and I cannot find that any of them iiave been 

 noticed by authors. Their characters may be summarized as fol- 

 lows : — 



I. Muzzle naked, D. I. 7. 



Muzzle with tentacles ; eye 3.33 times in interorbital space ; head 3^-^ times 

 in length (without caudal). Head wide. Black below, white-dotted. 



C. ALGA. 



II. Muzzle with a broad naked marginal band ; no tentacles ; D. I. 7. 

 Eye three times in interorbital width; head broad, short, 3.75 times in 

 length ; 1. 1. 23. Brown, with indistinct pale spots ; uniform below. 



* C. MALACOPS. 



Eye three times in front, head wedge-shaped, roofed in front, 3.5 times in 

 length ; naked band narrower ; blackish, white-dotted below. 



C. TECTIROSTKIS. 



[February 13, 



