SOUTH AMERICAN NEMATOGNATHI. 311 



mottled with darker, indistinctly striped; the fins in the 

 largest specimen margined with black, a white band 

 margining the black in the smallest specimen; dorsal fin, 

 inner surfaces of pectoral and ventral fins finely mot- 

 tled; a black axillary spot. 



Head 3k depth 5; Br. 10-11; D. I, 6; A. 34. 



Two specimens .42-. 50 m. Serpa; Villa Bella. Thayer 

 Exped. 



246, Ageneiosus axillaris. 



Ageniosus axillaris Giinther, Cat. Fish. Brit. Mus. 



(Surinam). 

 Habitat: Surinam. 



This species is known only from the type 



FAMILY IV. 



=Siluridce anomalopterce Giinther, Cat. Fish. 

 Mus. v, 3, 1864. 



=HypophtkalmidoB Cope, Proc. A. A. A. S. 1871. 



This family composed of two genera, is confined to 

 the northern Amazon and Guiana region of South Amer- 

 ica. 



The anatomy of the family has been studied by Prof. 

 R. Ramsay Wright. * 



The characterization of the family is given in the key. 



ANALYSIS OF THE GENERA OF HYPOPHTHALMID.E. 



a. Jaws and vomer with teeth. Helogenes Iv. 



aa. Jaws and vomer without teeth. Hypophthalmus Ivi. 



LV. HELOGENES. 



Helogenes Giinther, Annals and Magazine Natural His- 

 tory, xii, 443, 1863 (marmoratus) . 



Type: Helogenes marmoratus Gunther. 



* On the Skull and Auditory Organ of the Siluroid Hypophthalmus, 

 Trans. Hoy. Soc. Canada 1885, 107-118, plates viii-x. 



