150 SILURIDiE 



19. Arius troschelii. 



Sciades troschelii, Gill, Proc. Acad. Nat. Sc. Philad. 1863, p. 171. 



D. 1/7. A. 16. 



The height of the body is two-ninths of the total length (without 

 caudal) ; the length of the head enters three times in the length 

 before tho end of the anal fin ; its width equals the interval between 

 the snout and upper angle of praeoperculum. The maxillary barbels 

 extend to about the middle of the pectoral, the outer ones of the 

 mandible to its base. There are three villiform patches on the palate 

 which are almost contiguous, forming an arch : the median patch is 

 small, rather transverse, and widest towards the front ; the outer arc 

 oblong, sub triangular. The band of the upper jaw is quite wide, the 

 lower nearly half as wide as the upper. The dorsal spine equals that 

 of the pectoral, its length being two-thirds of that of the head. The 

 ventrals extend to the origin of the anal. Fins blackish. (Gill.) 



West coast of Central America. 



20. Arius emphysetus. 



Bagrus (Sciades) emphysetus, Mutt, ty Trosch. Hot: Ichth. iii. p. 8, and 

 in Schomb. Brit. Guian. iii. p. 627. 



B. 6. D. 1/7. A. 20. P. 1/11. 



Head flat, rounded in front ; its length is two-ninths of the total. 

 Eyes very small ; their distance from the end of the head is more 

 than twice as great as that from the snout. Head coarsely granu- 

 lated above ; its occipital process short, four times as broad as long, 

 joining the nuchal plate, which is very large, as broad as long, 

 heart-shaped. The teeth on the palate form a broad transverse 

 band, composed of three divisions : the middle on the vomer is square, 

 the lateral are tapering behind ; there is another band of teeth be- 

 sides, posteriorly and interiorly to the palatine teeth, inserted on each 

 side of the base of the skull. Upper jaW the longer ; barbels six, 

 flattened : the maxillary barbels extend beyond the dorsal fin, the 

 outer ones of the mandible to the pectoral. Dorsal spine very strong, 

 granulated, serrated at the top and posteriori}-. Adipose fin shorter 

 than dorsal. Poms axillaris very small. Ventrals shorter than 

 pectorals. (31. § T.) 



Surinam ; British Guiana. 



21. Arius valenciennesii. 



Bagrus albicans, Cuv. fy Val. xiv. p. 461. pi. 420 (not Arius albicans, 



Cm. 4- Val). 

 ? Bagrus valenciennei, Casteki. Anim. Amer. Sud, Poiss. p. 31.pl. 13. fig. 1 

 (see p. 154). 



D. 1/7. A. 19. P. 1/11. 

 The length of the head is one-fourth of the total length (without 

 caudal) ; head one-third longer than broad. The eye is thrice as 

 distant from the praeopercular limb as from the end of the snout. 

 Jaws equal in length anteriorly. Teeth on the palate in a broad 

 band, with a triangular patch on each side. The maxillary barbel 



