306 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



4.25 in head; snout 3.7 to 4.37; eye 4.65 to 6.8; mouth large; lower jaw 

 projecting; maxillary reaching past posterior margin of eye, mostly 

 slipping under suborbital; teeth as in preceding species; gill-rakers 

 poorly developed, 5 below angle on anterior arch; lateral line complete, 

 straight, occupying median line of side; scales large, regularly placed, 

 cycloid, 15 to 17 on median line in advance of dorsal; 9 scales across 

 caudal peduncle from one lateral line to the other; 4 complete rows of 

 scales between lateral line and anal fin; dorsal fin inserted midway 

 between tip of upper jaw and base of caudal or slightly nearer the 

 former; adipose fin wanting; caudal fin convex; anal fin inserted poste- 

 riorly, the longest rays not quite reaching base of lower caudal rays; 

 ventral fins inserted under base of dorsal, a little nearer base of caudal 

 than tip of lower jaw; pectoral fins inserted behind margin of preopercle, 

 failing to reach base of ventrals by 4 or 5 rows of scales. 



Color as in preceding species. 



Of this species 8 specimens were preserved. They range in length 

 from 85 to 295 mm. All are from the Rio Tuyra Basin. 



This species is closely related to the preceding, differing mainly in 

 the slightly larger scales. Our specimens were compared with specimens 

 from the Rio Atrato Basin, with which they appear to agree perfectly. 



Habitat: Rio Tuyra Basin; both slopes of Colombia; Ecuador, and 

 south to Brazil. 



Family VII. Gymnotidae. 



Body elongate, more or less eel-shaped; with or without scales; 

 vertebrae many; skull with or without a frontal fontanel; parietal fon- 

 tanel always present; mouth with or without teeth; margin of upper 

 jaw formed by maxillaries and premaxillaries; air-bladder in 2 parts, 

 connected by a small tube; vent well forward, never behind tips of 

 pectorals, usually under head; dorsal fin wanting, or represented by a 

 filament; caudal fin present or more usually absent, the tail terminating 

 in a pointed appendage when fin is wanting; anal fin very long; ventral 

 fins wanting; pectoral fins present, small. 



KEY TO THE GENERA. 



a. Frontal fontanel wanting. Gymnotus, p. 307. 

 aa. Frontal and parietal fontanels present. 



b. Caudal fin and dorsal filament wanting. 



c. Orbital margin free; teeth present in both jaws, in 2 more or less 

 distinct patches in upper jaw and in a single patch in lower jaw. 



Sternopygus, p. 308. 



