494 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



on the vertical passing through the origin of the first dorsal fin, from 

 which point the contours of the body extend forward and back- 

 ward in convex curves (more convex in some specimens than in the 

 type, the larger specimens being decidedly more robust than the 

 smaller ones). The ventral contour is gently curved. The greatest 

 width of the body is contained 2.8 (2.4 to 2.9) times in the head; the 

 greatest width of the head is equal to its depth through the hind 

 margin of the orbits, except in very large specimens. The lateral 

 outlines of the head are as figured for specimens of O. commutabiUs 

 with long snouts. 1 The dorsal contour of the snout is slightly con- 

 cave. Measurements of snout in head: preocular length, 2.28 (2.05 

 to 2.4) ; preoral length, 2.45 (2.25 to 2.9) ; width of base, at verticals 

 from front of orbits, 3.1 (2.95 to 3.35) ; width at end of ethmoid 

 portion of infraorbital ridge, 1.25 (1.1 to 1.33) in length of snout 

 anterior to that point. The figures of C. commutabilis given by Rad- 

 cliffe show the course taken by each of the spinous ridges of the head 

 for this species as well; the occipital ridges diverge both anteriorly 

 and posteriorly; the least distance between them is contained 2.05 

 (1.6 to 1.9) times in the interorbital space. Length of orbit: 3.6 (3.4 

 to 3.9) in head; 1.6 (1.5 to 1.9) in snout; 1.05 (1.0 to 1.3) in postorbital. 

 Least interorbital width, 1.25 (1.3 to 1.6) in postorbital; least sub- 

 orbital width, 2.35 (2.33 to 2.6). The upper jaw extends from below 

 the posterior nostril to the vertical passing through the eye behind 

 the pupils (to below the posterior orbital margin in the largest 

 specimen) ; the length of the upper jaw is contained 4.05 (3.3 to 4.7) 

 times in the head, being decidedly greatest in the largest specimens. 

 Length of barbel, 3.6 (3.6 to 5.6) in postorbital. Six branchiostegals ; 

 gill-membranes with a narrow free fold. The lower angle of the 

 subopercle is produced downward and backward into a pointed flap, 

 lying just above the angle of the preopercle. 



The distance between the center of the anus and the base of the 

 outer ventral ray is contained 4.0 (3.6 to 5.8) times in the head, 3.0 

 times in the very large specimens; the distance is only a little shorter 

 than the orbit in the type, but varies from decidedly shorter to about 

 one-third longer than the orbit, being longest in the largest speci- 

 mens. The distance between the ventral fin and the isthmus is con- 

 tained 3.75 (2.7 to 4.0) times in the head; the distance from the anus 

 to the isthmus, 2.05 (1.5 to 2.35) times. An oval or linear naked 

 ventral fossa extends forward from the anus for a distance only as 

 long as the peritroct. In the body wall between this fossa and the 

 peritoneum there lies a gland-like body, 2 truncate anteriorly, black 

 on its ventral surface and anterior edge, but silvery dorsally. 



1 Radcliffe, Proc. O. S. Nat. Mus., vol. 43, 1912, text figure 2 (p. 129) ; reprinted in 

 this report as text figure 27. 

 2 Dissected out in a paratype. 



