248 SILUKID^. 



posthumeral ridge very obtuse. Uniform blackish brown ; belly with 

 minute whitish dots. 

 Para. 



a-c. From 4 to 5 inches long. River Capin. Purchased of Mr. 



Stevens. 



18. Chsetostomus leucostictus. 

 D. 1/7. A. 4. P. 1/6. L.lat.25. 



Head much depressed, rather longer than broad; occipital and 

 nuchal regions without any prominence ; the length of the head is 

 more than one-third of the total (without caiidal). Snout broad, 

 much depressed, granulated above, with a narrow soft- skinned mar- 

 gin and with a few short tentacles. Eye of moderate size, its dia- 

 meter being two-fifths of the width of the interorbital space. Inter- 

 operculum with about seven non-flexible, short, curved spines, the 

 strongest being much shorter than the eye. Thorax and belly en- 

 tirely naked. Dorsal fin as high as long, the length of its anterior 

 rays being much less than that of the head ; the length of its base is 

 more than its distance from the second fin ; there are seven scutes 

 between the two fins. Caudal fin obhquely truncated ; the pectoral 

 spine extends to the base of the ventral. Eleven scutes between anal 

 and caudal ; the lateral scutes of the body with rough strite, but with- 

 out keel ; posthumeral ridge very obtuse. Black : pure white dots 

 are scattered over the whole body and over all the fins. 



Essequibo. 



ff. Three inches long From Mr. Ehrhardt's Collection. 



19. Chaetostomus calamita. 



Hypostomus calamita, Cuo. d^- Val. xv. p. 515. 



D. 1/7. A. 5. P. 1/6. L.Iat.26. 



Head much depressed, as broad as long, its length being one-third 

 of the total (without caudal) ; occipital and nuchal regions without 

 any prominence. Snout broad, much depressed, graniilatod on its 

 posterior half, with many tentacles on its anterior, soft-skinned half. 

 Eye rather small, its diameter being two -sevenths of the width of the 

 interorbital space ; the space between the eye and the operculum is 

 only partially granulated. Interoperculum with about fourteen non- 

 flexible curved spines, the longest of which is twice as long as the 

 eye. Thorax and belly entirely naked. Dorsal fin higher than long, 

 the length of its base beiag equal to its distance from the second fin ; 

 there are eight scxitos between the two fins. Caudal fin obliquely 

 truncated. Twelve scutes between anal and caudal ; the lateral 

 scutes of the body without keels, finely granulated; posthumeral 

 ridge very obtuse. Uniform brown. 



Peru. 



u. Adult. Rio Apurimac. From Mr. Pentland's Collection. — One 

 of the typical specimens. 



