95. CHJETOSTOMUS. 247 



II. Snout more or less naked. 



a. Dorsal fin eight-rayed. 



* Snout with tentacles. 



16. Chaetostomus cirrhosus. 



Hypostomus cirrhosus, Valenc. in cCOrbign. Voy. Am£r. Mtrid. Poiss. 



pi. 7. fig. 3; Cuv. 8f Vol. xv. p. 511. 

 Ancistrus cirrhosus, Kner, Hypostom. p. 272. 



D. 1/7. A. 5. P. 1/6. L. lat. 23-25. 



Head much depressed, occipital and nuchal regions without any 

 prominence ; the length of the head is contained twice and two- 

 thirds or twice and three-fourths in the total (without caudal). 

 Snout hroad, much depressed, nearly entirely covered with soft skin, 

 and provided with many tentacles in adult males ; females and young 

 specimens with only a few tentacles in front of the snout ; eye of 

 moderate size, its diameter being one-third or one-fourth of the width 

 of the interorbital space. Interoperculum with from nine to twelve 

 non-flexible curved spines, the strongest being longer than the eye. 

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

 the length of its base being a little more than its distance from the 

 second fin ; there are six or seven scutes between the two fins. Caudal 

 fin obliquely truncated. Eleven scutes between anal and caudal ; the 

 lateral scutes of the body without keels, with a spiny margin ; post- 

 humeral ridge very obtuse. Uniform blackish brown ; or covered all 

 over with yellowish dots, the ground-colour between them forming a 

 network. 



South America. 



a. Adult. Essequibo. From Mr. Ehrhardt's Collection. 



b. Adult. British Guiana. Presented by Sir R. Schomburgk. 

 c-cl. Adult and half-grown. From the Collection of the Zoological 



Society. 



17. Chaetostomus hoplogenys. 

 D. 1/7. A. 5. P. 1/6. L. lat. 25. 



Very similar to Ch. cirrhosus, but with shorter interopercular spines. 



Head much depressed, occipital and nuchal regions without any 

 prominence ; the length of the head is one-third of the total (with- 

 out caudal). Snout broad, much depressed, granulated above, with 

 a broad soft-skinned margin ; a series of short tentacles round the 

 margin. Eye of moderate size, its diameter being one-third or two- 

 fifths of the width of the interorbital space. Interoperculum with 

 eight or nine non-flexible curved spines, the strongest being rather 

 shorter than the eye. Thorax and belly entirely naked. Dorsal fin 

 rather higher than long, the length of its anterior rays being 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 obliquely truncated ; the pectoral spine extends backwards to the 

 second third of the ventral fin. Ten scutes between anal and caudal ; 

 the lateral scutes of the body with rough stria), but without keel ; 



