SOUTH AMERICAN NEMATOGNATHI. 389 



azon, uear Rio Negro; Calabozo); Eigenm. & Eigenm. Proc Cal. 

 Acad. 2d Ser. ii, 40, 1889 (Teffe; Obidos; Manacapuru; I(;a; Rio 

 Negro). 



Hypoj)topoma bilohatum Cope, Proc. Am. Philos. Soc. xi, 1870, 

 566, fig. (Pebas, Ecuador); id, 1. c. xvii, 1878, 679 (Peruvian Am- 

 azon); Steindachner, Denk. Ak. Wien, xli, 48, pi. vi, 1879 

 (Obidos; Lago Alexo; Manacapnru); id. Flusfissche, Stidam. 

 iv, 7, 1882 (Rio Huallaga). 



Otocinclus joherti Vaillant, Bull. Soc. Philom. 7th Ser. iv, 147, 1880 

 (Calderon). 



Habitat: Solimoens, Marafion and northward. 



We are unable to detect any constant differences be- 

 tween thoracaturn and bilohatum. Dr Giinther's speci- 

 men had a damaged caudal. The figures of bilohatum 

 by Cope and by Steindachner do not agree in coloration, 

 ventral covering, etc. 



Body subterete, the greatest depth equal to the greatest 

 width. Head greatly depressed forward, its width equal 

 to the length of snout and eye; profile little concave in 

 front, somewhat convex on occiput; interorbital a little 

 convex; occipital ending in a triangular process which 

 is bordered by 3 nuchal plates; prefrontals arrow-shaped. 

 Snout margined by a rhomboidal plate at tip and 4 

 plates between it and the eye; a series of small plates 

 and sometimes a narrow naked area from the nares for- 

 ward; marginal plates of the snout with booklets above 

 and larger ones below. 



Eye 3 in snout, 6 in head, 3J-4 in the interorbital. 



Two small plates below the 2d marginal plate in front 

 of the eye, a much larger plate below the eye and 4 

 small plates between the gill-openings. Belly covered 

 with 6-7 pairs of plates, a small median one connects 

 the anterior 2-3 pairs, a large shield-shaped plate be- 

 tween the ventrals. 



In a specimen (No. 7760) .05 m. long to base of cau- 

 dal, there are no plates between the gill-openings, the 

 ventral armature consists of 6 pairs of plates confined to 

 the sides and 5 roundish plates along the middle. 



