SOUTH AMERICA.N NEMATOGNATHI. 53 



19. Pygidium nigricans (Cuv. k Val.) 



20. Pygidium amazonicum (Steiudaclmer). 



ly. Eremophii.us Humboldt. 

 Thricomyvterus Humboldt; Trachypoma Giebel. 



21. Eremophilus mutisii Humboldt. 



Trachypoma marinoratum Giebel. 



Y. Tridens gen. iiov. 



Type, Tridens mdanops sp. uov, 



Yeiitrals small, nearer tip of snout than to base of caudal. 

 Anal long, inserted in front of the dorsal fin. Head greatly 

 depres>ed, the eye infringing on its lower and upper sur- 

 faces. A series of fine labial teeth; stronger teeth on the 

 jaws. Gill membrane united, forming a broad free fold 

 across the isthmus. Opercle and preopercle armed. Max- 

 illary barbels 2, 



22. Tridens melanops sp. nov. 



Tj'pes, No. 8137; twenty- seven specimens, the largest .027 m. long. 

 Iga. James, 



Body compressed, extremely slender. Head broad, tlie 

 snout rounded; mouth broad, inferior. Opercle long and 

 slender, terminating in tiiree spines, trident shaped. Pre- 

 opercle with similar but smaller spines. Barbels minute, 

 scarcely evident. 



Distance of origin of dorsal fin from extremity of caudal 

 3 in the length; origin of anal fin from extremity of caudal 

 2^- in the length. Anal rays rapidly decreasing in height 

 backward, its last ray about over the last ray of the dorsal. 

 Caudal rounded, without accessory rays. 



Yellowish, a series of black spots along the base of the 

 anal; posterior half of the caudal fin dusky. 



Head 9; depth 13; D. 10-12; A. 20-25. 



