EIGENMANN: the freshwater fishes of BRITISH GUIANA 423 



Gymnotidce Cope, Proc. Am. Ass. Adv. Sci., XX, 1871, 333. 



Eel-like fishes without a dorsal fin and a very long anal fin. 



Key to the Guiana Genera of Gymnotidce. 



a. No frontal fontanel; no dorsal filament; no true caudal fin; lower jaw projecting; head depressed; teeth 

 conical, in sockets. 



b. Anal basis extending around the end of the tail, forming a false caudal; electric organs well-developed; 



body not scaled. (Electrophorina:.) Electrophorus. 



66. Anal ba-sis not extending around the end of the slender cylindrical tail; electric organs wanting; body 



scaled. (Gymnotince.) Gymnotus. 



aa. T>arge frontal and .parietal fontanels; lower jaw not projecting; head not depressed; teeth if present villi- 

 form, in patches, and without deep sockets. 



c. No caudal fin; tail beyond the anal fin, slender, pointed; no dorsal filament. 



rf. Sides of the entire body scaled. (Sternopygirue.) 

 e. Snout short, not tubular. 



/. Orbital margin free; teeth in both jaws; air-ijladder long and conical Stemopygus. 



//. Orbital margin not free. 



g. Teeth in both jaws; much compressed; air-bladder short and subspherical. 



Eigenmannia. 

 gg. No teeth; body subcyHndrical. 



h. A cylindrical filament in a groove on each side of the mental region; head chubby. 



Steatogenys. 



hh. No filaments as above; head rather pointed Hypopomus. 



ee.. Snout tubular; without free orbital margin; very much compressed and elongate. 



Rhamphichthys. 



del. Anterior portion of the sides without scales Gymnorhamphichthys. 



cc. With caudal fin; tail short; without free orbital margin; a dorsal filament; teeth in patches on one or 

 both jaws. {Sternarchince.) 

 i. Caudal at the end of a peduncle; anal not reaching caudal. 

 j. Snout much produced; teeth in both jaws. 



k. Snout decurved Stemarchorhynchus. 



(kk. Snout straight Stemarchorhamphus.) 



jj. Snout heavy and blunt, not produced. 

 I. Teeth in one or both jaws. 

 m. Teeth in both jaws. 



n. Back scaled completely, or at least for some distance in front of the dorsal 

 filament. 

 0. Gape long, angle of the mouth little if any in front of the eye; snout long. 



Stemarchus. 

 (oo. Gape .short, angle of the mouth below the anterior or posterior nostrils; 



snout short StemarcheUa.) 



nn. Back naked to beyond the dorsal filament; scales along the lateral line large. 



Porotergus. 



mm. Upper jaw without teeth, those of the lower jaw in a single series; snout very short. 



Stemarchogiton. 



