250 SILURIDiE. 



Thorax and belly entirely naked. Dorsal fin as high as long, the 

 length of its base being equal to its distance from the caudal. Caudal 

 fin obliquely truncated. Scutes of the body with a spiny margin, 

 without keel. Brownish, the lower side with brown dots. (Kner.) 

 Barra do Rio Negro. 



** Snout without tentacles; upper labial fold not dilated in the middle. 



24. Chsetostomus microps. 

 Hypostomus erinaceus, Giinth. Proc. Zool. Soc. 1859, p. 420(not synon.). 

 D. 1/9. A. 4. P. 1/6. V. 1/5. L.lat.24. 



Head and nape much depressed, without any prominence; the 

 Avidth of the head equals its length, and is one-third of the total 

 (without caudal) ; the entire margin of the snout is naked, soft, and 

 swollen, without tentacles, the fold of the upper lip being short, and 

 not prolonged in the middle ; barbel very short. Eye very small, its 

 diameter being about one-ninth of the length of the head, and less 

 than one-third of the width of the interorbital space. Interoperculum 

 with a bundle of about ten erectile spines, which arc neither flexible, 

 nor curved at the end ; the longest are longer than the eye. Thorax 

 and abdomen entirely naked. The dorsal fin is considerably longer 

 than high, the length of its anterior rays being only two-thirds of 

 that of the head ; the length of its base equals its distance from the 

 caudal fin ; there are six scutes between the two dorsal fins. Caudal 

 fin obliquely truncated ; anal very small ; ten scutes between anal 

 and caudal. Pectoral spine of moderate strength, extending to the 

 root of the ventral fin. Scutes of the body not keeled, provided with 

 comparatively long spines along the margin ; posthumeral ridge very 

 indistinct. Uniform blackish brown ; rays of the dorsal and caudal 

 fins annulated with black. 



Andes of "Western Ecuador. 

 a-c/. From 21 to 31 inches long. From Mr. Fraser's Collection. 



*** Upper labial fold much dilated in the middle. 

 25. Chsetostomus loborhynchus. 



Heckel, in Tschudi, Faun. Per., Fische, p. 26. taf. 4. 

 D. 1/8. A. 4. L. lat. 25-26. 



Head much depressed, without eminence on the occiput, nearly as 

 long as broad. Snout granulated above, with a broad, swollen, soft- 

 skinned margin in its whole circumference. The fold of the upper 

 lip very broad, broadest in the middle. Tentacles none. Teeth very 

 fine, not notched at their extremity. Eye small, its diameter being 

 two-fifths of the width of the interorbital space. Opercular margin 

 and interoperculum with rather short spines, eleven on the latter. 

 The pectoral spine is as long as the head, and extends somewhat 

 beyond the root of the ventral. Scutes without keels. Brown. 



Rio Tullumayo (Eastern Andes). 



