252 The South American Cat-fishes 



to 2^ in snout, 3 to 3| in the head, tliR interorbital width about 1^ in the 

 orbital diameter. 



Maxillary barbels reaching the gill openings, or beyond, except in the 

 old ; all the barbels united by a membrane ; the mental barbels short, their 

 bases thickened and covered with short fleshy cirri. 



Snout covered with skin ; posterior nares about equidistant between 

 the anterior nares and the eye, the anterior nares about equidistant be- 

 tween the eye and tip of the snout ; mouth very small, wholly inferior; a 

 very small patch of villiform teeth on each intermaxillary, a larger patch 

 on each dentary bone. Gill openings rather wide, the isthmus about 

 equal to the orbital diameter. Coraeoid bones covered with skin. 



Lateral scvites low, highest above the anal, their height about ^ the 

 orbital diameter, gradually becoming smaller each way. Each scute with 

 a median hook. 



Distance of the dorsal fin from the snout 2^ to 2| in the length ; dorsal 

 spine 1^ to Ij in the head, serrate on both margins, most coarsely on the 

 inner, the sides triate. Interdorsal space 3 to 3^ in the length. 



Caudal fin forked, it rays leathery ; accessory rays 10 or 11, the last 

 forming a small plate above and below on the caudal peduncle, the long- 

 est rays 1^ to 1^ in the head ; upper lobe of caudal longest. 



Anal slightly emarginate, its highest rays 2 to 2^ in the head. 



Ventrals not reaching the anal, about two in the head. 



Pectoral si^ine strong, serrate on both margins, most coarsely on the 

 inner ; sides striate. 



Numerous small pores in the axil and beneath the lower margin of the 

 humeral process as in the other species of this genus. Humeral process 

 broad and strong, reaching little beyond the middle of the pectoral spine, 

 its surface striate. 



Color dark above, lighter below ; dorsal fin with a black spot on the 

 upper half extending from the spine to the third ray. Pectorals and 

 anal usually with minute dots. Pectorals dusky above, lighter below. 

 1703, 1704, 1705, . 



Trocera on Tocaiitins, Brazil. Four specimens. Collected by 

 C. F. Hartt. 



AUCHENTPTERIN^. 



13. Tracliycoi'ystes striattilus (Steind.) Six specimens. 1710. 

 1711, 1712, 1713, 1714, . Eio San Francisco and Marajo. 



Ageneiosin.e. 



14. Ageiieiosiis valeiicieiiiiesi Bleeker. 1730. Brazil. 



PYGIDIID.E. 



15. Pygidiiiiii rivulatuiii (Cuv. & Val.) One specimen. Lake 

 Titicaca. 



i 



