194 
U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
back and belly being arcbed. The greatest depth is about a third of the length ; the peduncle 
of the tail is slender and short. 
The head is sub-conical and rather pointed forwardly. It is slightly depressed above the 
orbit, otherwise its profile would form a regular curvilinear prolongation of the dorsal outline. 
The mouth is rather small, the premaxillaries moderately protractile, and the lower jaw 
projecting slightly beyond the upper when the mouth is partially open : otherwise the jaws 
may be termed equal, the gape of the mouth being somewhat oblique when both jaws are in 
a retracted state. The posterior extremity of the maxillary does not quite reach a vertical line 
passing immediately in advance of the orbit. The teeth are of medium development, sub- 
conical or slightly club-shaped, and occupying the entire circumference of the mouth. On the 
inner row of the upper jaw they are often so small as to defy observation. The nostrils are 
nearly equal, situated towards the upper surface of the snout, a little nearer the anterior 
rim of the orbit than the extremity of the snout. The eye is proportionally large, circular 
in shape, and its horizontal diameter contained somewhat less than four times in the length of 
the side of the head, exactly once between the orbit and the end of snout, and a little less than 
twice between tbe orbit and the thoracic belt. There are three rows of irregularly imbricated 
scales on the cheeks, and four or five on the opercle. The branchiostegal rays, five on either 
side, are small, and concealed under the opercular apparatus. 
A vertical line drawn from the origin of the dorsal fin passes immediately behind the base of 
the pectorals. Nine or ten rays constitute the spinous portion, gradually higher from the first, 
which is the lowest of all, to the fourth or fifth, which is the highest; thence diminishing 
again to the last, which is a little shorter than the first articulated ray. The remaining portion 
of this fin occupies a base nearly double the length of that over which the spines extend. The 
articulated rays are very slender, and bifurcate but once beyond the half of their depth. The 
caudal fin is deeply forked, and its rays sub-divide three times upon their length. The anal 
is long and low, provided anteriorly with three small spines. The anterior articulated rays 
are not all divided : from four to eight in the female, and six to eleven in the male, are simple ; 
the rest bifurcate once, as in the caudal fin. In the male the simple and divided rays are 
separated by a triangular space, the undivided ones inclining anteriorly, the bifurcated 
posteriorly. The origin of the anal is opposite the fifth articulated ray of the dorsal, and 
extends a little more posteriorly than the latter. The origin of the ventrals is placed under 
the vertical line of the second or third dorsal spine. The external spine is slender and acute ; 
the articulated rays sub-divide three times. The pectorals are well developed, their extremity 
reaching the vertical of the second articulated ray of the dorsal, and a little beyond the tips of 
the ventrals themselves. Partial traces of a bifurcation of the third degree may be observed 
towards the extremities of their rays. 
Formula of the fins : 
Br. V: Y; $ D IX or X, 20 or 21; A III, 8 + 14 = 22 ; C 3, 1, 6, 6, 1 2 ; V I, 5 ; P 19. 
$ D IX or X, 19 or 20; A III, 11 + 13 = 24; C 3,1, 6, 6, 1, 2 ; V I, 5; P 18 or 19. 
The scales are proportionally large ; about four rows may be counted above the lateral line 
and twelve beneath it. The lateral line itself contains from forty to forty-four scales, and runs 
nearly parallel to the outline of the back. The dorsal groove extends from the highest dorsal 
spine to about the middle of the length of the articulated portion of the same fin. The sheath 
