2'M SILURID^. 



caudal) ; margin of the snout granulated, except in the middle of its 

 extremity, where it is naked ; a ridge runs from the ixpper angle of 

 the orbit to below the nostril ; occiput elevated, with two keels, each 

 terminating in a point. The free margin of the interoperculum with 

 small spines. Thorax and beUy naked ; scutes of the body keeled ; 

 there are twelve scutes between anal and caudal. The outer pectoral 

 rays extend beyond the base of the ventrals, and are armed with 

 bristles. A few scattered round spots on the head, body, and fins ; 

 they are smallest on the head. (Kne)\) 



Rio Guapore. 



This species is kno^ni fi-om a single example only ; it is 3 inches 

 long. 



3. Plecostomus horridus. 



Hvpostomus horridus, Kiicr, Hi/postom. p. 259. taf. 1. 

 PHj'postomus emarginatus, Kner, Hi/postom. p. 260 (female ?) (not 

 Cuv. Sf VaL). 



D. 1/7. A. 5. P. 1/6. L. lat. 27-28. 



Head rather depressed, its length being a little less than one-fourth 

 of the total (without caudal) ; occiput with a slight prominence. Eye 

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

 iuterorbital space. Interoperculum not armed. Throat, thorax, and 

 belly covered with very smaU scutes. Dorsal fin rather higher than 

 long, the length of its base being much less than its distance from 

 the second dorsal. Caudal fin deeply emarginate, its outer rays being 

 •armed with long setiform curved spines, like the outer pectoral ray. 

 The latter does not quite extend to the base of the ventral fin. Fifteen 

 scutes between the anal and caudal fins. The lateral scutes of the 

 body slightly keeled, each keel terminating in several small hooks. 

 All jjarts with roiind black spots, those on the head being the smallest ; 

 there are two series of these spots in each interradial space of the 

 dorsal fin. {Kner.) 



Rio Guapore. 



4. Plecostomus commersonii. 



Lacepede, v. pi. -4. fig. 2. 



Ilj'postonius commersonii, Valenc. in (VOrb. Voy. Amer. Stid, Poiss. 



pi. 7. fig. 2 (not good) ; Ciw. ^ Val. xv. p. 495. 

 PHypostomus commersouii, EJner, Hypostoni. p. 262. 

 Hvpostomus subcarinatus, Casteln. Anim. Amer. Sud, Poiss. p. 42. 



Vl. 21. fig. 1. 



D. 1/7. A. 5. P. 1/6. V. 1/5. L. lat. 30. 

 Head not much depressed, its length being two-sevenths of the 

 total (without caudal) ; no ridge between eye and nostril ; occiput 

 with a rather elevated obtuse ridge ; the median scutes of the nape 

 elevated in the middle and obtusely bicarinate. The middle of the 

 extremity of the snout is naked ; labial fold of moderate width, not 

 notched behind, covered with minute papilla;. Interoperculum with- 

 out any spines. The entire lower side of the head, thorax, and belly 



