SOUTH AMERICAN NEMATOGNATHI. 45 



//. Lower jaw longer; occipital process wider and shorter 

 than in proops, its tip reduced; dorsal plate more or less 

 crescent-shaped. Eye nearer snout than in proops. 

 Head flat, especially forward; opercle strongly granular; 

 humeral process obtuse, higher than long, granular; 

 dorsal and pectoral spine granular in front, weakly ser- 

 rate behind; ventrals longer than pectorals; D. I, 7; A. 

 17.* (Cuv. & Val.) passany 31. 



III. Jaws equal; dorsal plate large, almost as wide as the 

 skull behind eye; opercle striate; top of head granular 

 forward to between eyes; a triangular smooth area in 

 front; humeral process, dorsal plate and outer margins 

 of dorsal and pectoral spines granular. Snout 3 in space 

 from eye to preopercle; eye 5 in interocular space. Max- 

 illary barbels scarcely reach gill-opening. Adipose almost 

 as long as anal. Caudal lobes subequal, 5-J in the total 

 length. Head 4f in the total, its width 1J in its length. 

 D. I, 7; A. 19. t (Cuv. & Val.) albicans 32. 



ff. Posterior nasal openings connected by a membrane; dorsal 

 plate and occipital process truncate where they meet, at least 

 in the adult: in the young the dorsal plate is somewhat convex 

 in front, the backward projecting angles of the palatine patches 

 not developed. (SELENASPIS.) 



m. Occipital process half as wide at tip as at base; its length 

 more than half as long as its width; gill-rakers 5-j-lO. 



herzbergii 33. 



mm. Occipital process two-thirds as wide at tip as at base, its 

 length less than one-half its greatest width; gill-rakers 7-{-15. 



dowi 34. 

 ee. Teeth on the palate granular. 



n . Margin of dorsal plate and of occipital process convex where they 

 meet; palatine patches of teeth connected by the vomerine 

 patch in front, their inner margins not touching behind. 



luniscutis 35. 



nn. Dorsal plate emarginate in front receiving the pointed occipi- 

 tal process; palatine patches either separate or united for their 

 whole length. (Bleeker.) parkeri 36. 



dd. Dorsal plate crescent shaped, not enlarged. 

 o. Occipital process narrowed or constricted at base. (NoTARius.) 

 p. Occipital process narrowly and deeply constricted at base, its 

 margins regularly and strongly convex. grandicassis 37. 



pp. Occipital process broadly and deeply constricted, wider near 

 tip than in the middle, its margins describing a double curve, 

 convex toward tip, concave toward base. 



grandicassis parmocassis 37a. 



*Based on a specimen .91 m. long. 

 tBased on a specimen .61 m. long. 



