244 SILURIDiE. 



cated. Interopercular spines long, setiform. Brownish : body and 

 fins with numerous small round white spots. 

 Rio Araguay. 



8. Chsetostomus scaphirhynchus. 



Ancistrus scaphirhynchus, Kner, Hypostom. p. 280. taf. 3. fig. 2. 



D. 1/7. A. 6. L. lat. 25-26. 



Head much depressed, without prominence on the occiput, longer 

 than broad, its length being one-third of the total (without caudal). 

 Snout very broad, very obtusely rounded in front, with the margin 

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

 less than one-thii'd, of the width of the interorbital space ; super- 

 ciliary margin elevated. Interoperculum with from fifteen to eighteen 

 setiform spines. Lateral scutes of the body with a serrated keel ; 

 thorax and belly naked ; thirteen scutes between anal and caudal. 

 Dorsal fin longer than high. Pectoral spine nearly as long as the 

 head, extending somewhat beyond the root of the ventral. Caudal 

 obliquely truncated, the lower lobe being one-third longer than the 

 upper. Brown. (Knir.) 



Barra do Rio Negro. 



** Scutes of the body without distinct keels; dorsal fins distant. 



9. Chsetostomus mystacinus. 



Ancistrus mystacinus, Kner, Hypostom. p. 276. 

 D. 1/7. A. 6. L. lat. 22-23. 



Head much depressed, without prominence on the occiput; its 

 length is one-third of the total (without caudal) : eye of moderate size, 

 its diameter being nearly one-third of the width of the interorbital 

 space. Margin of the snout granulated, with very short, but rather 

 thick bristles ; interopercular region with long fine bristles partly 

 covering the interopercular spines, which are about twenty in number, 

 long, setiform, and curved at their extremity. Scutes spiny, the 

 spines being arranged in Lines, not keeled ; posthumeral ridge ob- 

 tuse. Dorsal fin nearly as high as long ; the pectoral spine extends 

 to the base of the ventral, and is rather shorter than the head. 

 Caudal forked, its lower lobe being the longer. Greyish olive : four 

 or five large roimd black spots along each dorsal ray ; the upper lobe 

 of the caudal with similar spots, the lower entirely black. {Kner.) 



Caraccas. 



10. Chaetostomus oligospilus. 



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



Head not depressed, as broad as long, its length being contained 

 thrice and a fourth in the total (without caudal) ; a very distinct 

 short ridge runs from the upper angle of the orbit to below the nos- 

 tril ; occiput with a slight longitudinal prominence. Orbital margin 

 rather elevated ; eye of moderate size, its horizontal diameter being 



