59. ARius. 171 



^. American species. 



59. Arius nuchalis. 

 D. 1/7. A. 21. P. 1/10. 

 The height of the body is one-fifth of the total length (without 

 caudal), the length of the head one-fourth. Head as broad as high, 

 its greatest width being two-thirds of its length ; its ^ ^ 



upper surface is granulated : the occipital process is 

 triangular, as long as broad, with the lateral margins 

 slightly concave ; it is elevated into an obtuse ridge 

 running along the middle ; the longitudinal groove 

 in the middle of the forehead is rather wide, narrow 

 behind, and does not extend to the base of the occi- 

 pital process. The teeth on the palate are coarsely 

 granular, and form two subtriangular patches 

 of moderate extent, which, sometimes, are subcontinuous 

 with their anterior angles. The maxillary barbels extend 

 nearly to the end of the pectoral. Dorsal spine of moderate 

 strength, slightly serrated along both edges, five-sixths of the length 

 of the head. Adipose fin small, shorter than the dorsal. Pectoral 

 spine as long as, but stronger than, that of .the dorsal. Pectoral fin 

 shorter than the head. 



British Guiana. 

 a-c. Six inches long. Purchased of Mr. Scrivener, 

 d-f. Young. Presented by Sir R. Schomburgk. 



60. Arias laticeps. 

 D. 1/7. A. 22. P. 1/10. 



The height of the body is contained four times and two-thirds in 



the total length (without caudal), the length of the head four times. 



Head broader than high, its greatest width being 



three-fourths of its length ; its upper surface is 



granulated : the occipital process is triangular, as 



long as broad, with concave lateral margins ; its 



median ridge is scarcely elevated ; the longitudinal 



groove in the middle of the forehead is narrow, 



tapering behind, and docs not extend backwards to 



the base of the occipital process. The teeth on the 



_ palate are granular, and form two small, 



^•^■^■-^ separate patches anteriorly on the palate. The maxillary 



/? *^ barbels extend to the middle of the pectoral. Dorsal spine 



of moderate strength, scn-ated posteriorly, three-quarters of 



the length of the head. Adipose fin small, shorter than the dorsal. 



Pectoral spine shorter and stronger than that of the dorsal fin. 



Ventrals white. 



Bi-itish Guiana ; Trinidad, 

 rt. Five and a half inclies long. British Guiana. Purchased of Mr. 



Scrivener. 

 h. Eight inches long. Trinidad. Presented by C. Taylor, Esq. 



