SOUTH AMERICAN NEMATOGNATHI. 315 



H. longifilis was based on specimens of from .13-. 15 

 m. in length and accordingly the maxillary barbels ex- 

 tend beyond the dorsal. 



H. TYiarginatus and H. edentatus were based on speci- 

 mens .25-. 35 m. long and the maxillary barbels are 

 slightly longer than the head and not extending to the 

 end of the pectoral. 



We do not know the length of the type of H. fimbriatus. 



This may be sufficient to prove that the different 

 "species" of Hypophthalmus are different stages of the 

 same species. 



The nine specimens examined are from Para. 



Body much compressed; greatest width of head 2|-3 

 in its length, its greatest depth 2^; profile straight and 

 steep; mouth horizontal, placed low. 



Eyes 9-13 in head, 5-6 in snout, 2i-4 in the space be- 

 tween the eyes measuring below. 



A long groove from occiput widening forward. 



Upper jaw thin, papery; no teeth. 



Maxillary barbels inserted in front of anterior nares; 

 reaching adipose fin in young, scarcely beyond head in 

 adult examples; all the barbels flattened and having their 

 posterior margins membranaceous, especially in the 

 young; the mental and postmental barbels reaching to 

 the tip of the dorsal in the young, shorter in the adult. 



Gill-membranes separate to below the maxillary; gill- 

 rakers slender, about two diameters of the eye in length, 

 very numerous. 



Lateral line prominent, sending branches downward 

 and backward to below the level of the pectorals, and 

 others backward and upward; each set of branches ex- 

 tending across the lateral line — the one upward and 

 forward, the other forward and downward to the second 

 branch in front of it, forming a network along each side 

 of the lateral line; the branches becoming irregular on 



