544 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



There can be little question as to the naturalness of this group of 

 species, although they have been described as members of the follow- 

 ing diverse genera : Macrourus, ptonurus, Malacocephalus, Cory- 

 phcwnoides, Chalimtra. 



KEY TO THE SPECIES OF ^ ENTRIFOSSA. 



a 1 . A sealeless ventral fossa, not pearly, nor lens-like, situated between the 

 ventral fins, of variable size, and usually separated by a more or less com- 

 plete scaly bridge from the peritroct ; mouth little oblique; spinules on 

 scales arranged in quincunx order. 

 6\ Teeth of lower jaw in two series ; canines of upper jaw arrow-shaped ; 

 denticulations of dorsal spine obsolescent; scales with a few short 



spinules; orbit about 3 in head (Atherodfs, new subgenus.) 



atherodon. 1 

 b 2 . Teeth of lower jaw in three or more series, forming a narrow band ; denti- 

 culations of dorsal spine numerous and sharp ; scales beset with numer- 

 ous spinules (Subgenus Ventrifossa. ) 



f 1 . Sides of head and body brownish, with little or no silvery; scales small. 



d\ Preopercle not produced backward at its angle ; outer ventral ray 



filamentous; upper jaw shorter, its length 2§ in heii(\--macroneinus. 



d 2 . Preopercle produced backward at its angle ; outer ventral ray not 



filamentous; upper jaw longer, its length 2£ in head misakia. 



(?. Sides of head and body bright silvery ; scales of moderate size. 



e\ An area of enlarged spineless scales behind first dorsal ; eye about 4 

 in head ; 6 rows of scales from last ray of first dorsal to lateral 

 line; first dorsal black, with a white base and tip (Alcock). 



petersonii. 

 (?. No area of enlarged or spineless scales behind first dorsal fin ; orbit 

 3.5 in head, or larger. 

 f. Preopercular ridge not sharply produced backward. 



g 1 . First dorsal fin with a distinct black spot ; ventrals blackish. 

 h 1 . Ventral fossa very small, as in garmani, its front being behind 

 the bases of the outer ventral rays ; barbel about % as long 



as the snout nigrodorsalis. 



h 2 . Ventral fossa of moderate size, its front being in line with the 



outer ventral rays _> ctenomelas. 



g*. First dorsal fin without a distinct black spot; ventrals paler; 

 ventral fossa small ; barbel longer than the snout, being con- 

 tained 2.S to 4.0 times in the head. 

 l\ 7 to 9 series of scales separating the front of second dorsal 

 from lateral line row; interorbital width less (0.20 to 0.23, 



usually 0.21 or 0.22 of length to anus divergens. 



V. 6 series of scales above lateral line; interorbital wider (0.22 to 



0.29, usually 0.25 to 0.27 of length to anus) <i<tnn<nu. 



f. Preopercular ridge sharply produced backward at its angle. 



occidotlalis. 



a 2 . A lens-like organ immediately before anus, and another between the ventrals, 



much as in Uymenocephalus ; mouth little oblique; spinules on scales 



arranged along parallel series Lt-cioadeij.a. new subgenus.) 



nigromarginata. 



J This species approaches the genus Malacocephalux most closely. 



