in the Collection of the British Museum. 477 



length being more than one-third of the total (without caudal). 

 The horizontal diameter of the orbit is more than one-half of 

 the width of the interorbital space, and about one-fifth of the 

 length of the head. Margin of the snout granulated, without 

 bristles ; interoperculum with a bundle of about twenty seti- 

 form spines, the longest of which are about one-fourth of the 

 length of the head, and extend backwards to the root of the 

 pectoral fin. Thorax and belly entirely naked. Twelve scutes 

 between the anal and caudal fins. Scutes of the body without 

 keels, but with vertical series of spines, the anterior scutes 

 with one series only, the middle with two, and the posterior 

 with three or more. Blackish brown ; head and body with 

 numerous indistinct round yellowish spots, each about as large 

 as the pupil ; each dorsal ray with a series of round whitish 

 spots, the black ground-colour forming a network on the fin. 



Surinam. 



Chcetostomus dentex. 



Interoperculum with a bundle of about ten straight setiform 

 spines, the longest of which is as long as the eye. Thorax 

 and belly nearly entirely naked, there being only a few granu- 

 lations behind the throat. Teeth comparatively large, with 

 the apex dilated, scarcely lobed ; there are about six on each 

 side in the upper jaw, and three in the lower. Scutes not 

 keeled, but covered with strong spines. Uniform greyish 

 brown. 



Xeberos. 



Hypoptopoma (g. n. Hypostomatin.). 



This genus differs from Plecostomus in the peculiar forma- 

 tion of the head, which is depressed, spatulate, the eyes being 

 on the lateral edge of the head. The moveable gill-covers are 

 reduced to two bones, viz. : — the operculum, small and placed 

 as in Plecostomus ; and a second, larger bone (interoperculum ?), 

 separated from the eye by the narrow suborbital ring, and 

 placed at the lower side of the head. 



Hypoptopoma thoracatum. 

 D. II 1. A. 6. P. 1/6. V. 1/5. L. lat. 24. 

 Xeberos. 



Loricaria lanceolata. 



Head and body much depressed, but narrow, the greatest 

 width of the head being three-fifths of its length. Lower lip 

 broad, slightly notched behind, fringed. Teeth very fine, few 

 in number, about five on each side in the upper jaw, and about 

 seven in the lower. Orbit with a rather shallow notch behind, 

 its horizontal diameter (the notch included) being two-thirds 



