3G8 
U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
elevated at the inner part than at the outer; the inner part having, moreover, a longitudinal keel, the outer part constituting a 
rounded process, directed towards the point of the tooth. First dorsal fin placed between the pectorals and the ventrals; the 
second between the ventrals and the caudal fin. Upper lobe of caudal larger than the lower; sometimes a caudal groove or 
furrow is observed. In the male a movable spine or thorn, bent upon its apex, may be seen at the outer edge of the extremity 
of the ventral appendages. The scales are sub-cordiform, posteriorly acute, with one or several keels. 
Syn.- Jicanlliias, Risso, Hist. nat. Eur. merid. Ill, 1826, 131 — Mull. &Henle, Syst. Beschr. Plagiost. 1841, 83.— 
Storer, Synops. 1846, 254.— Dum. Ichthyol. analyt. 1856, 133. 
Of all the genera of Spinacidae, the genus Spinax is the one to which Acanthias bears the 
closest affinities, the latter having been admitted by comparatively few writers. 
ACANTHIAS SUCKLII, Grd. 
Spec. Char. —Head constituting somewhat more than the sixth of the entire length. Snout very much depressed and 
elongated ; nostrils nearer its apex than the angle of the mouth. Eyes large, elliptical, situated immediately in advance of the 
mouth. Anterior margin of first dorsal fin nearly equidistant between the pupil and the anterior margin of the second dorsal. 
A shallow caudal groove along the base of the upper lobe of the caudal. Dark greyish, with a few light irregularly scattered 
spots. 
Svn. — Spinax ( Acanthias ) suckleyi, Grd. in Proc Acad Nat. Sc. Philad. VII, 1854, 196. 
We have examined one specimen of this species measuring nearly two feet and a half in total 
length, the head forming a little more than the sixth part of it. The body is very much 
elongated, slender, and gradually tapering posteriorly. The snout is very much depressed, 
elongated, and, when viewed from above, sub-conical in its outline. The nostrils consist of a 
circular free aperture, and of a transverse split continuing it inwardly. At the anterior edge 
of this split may be observed an elongated flap, tapering and rounded off, which overlaps 
the split at the inner edge of the circular aperture ; the rest of the anterior edge of the split, as 
well as the entire posterior edge, exhibits a narrow, thin membranous expansion more developed 
at the posterior edge than at the anterior. The nostrils themselves are somewhat nearer the 
apex of the snout than the angles of the mouth. The latter is large ; measured from angle to 
angle, it is a little less than the rostral distance from the middle of the anterior jaw forwards. 
The cartilaginous fold of the posterior (inferior) angle is shorter but thicker than the outer one 
at the anterior (superior) lip. The inner one at the same anterior lip is very slender and mostly 
covered by the outer one. The eyes are very large, elliptical, their longitudinal diameter 
entering about four times along the distance between the apex of the snout and the spiracles ; 
they are situated immediately in advance of the mouth. A longitudinal groove may be seen 
at the anterior and at the posterior rim of the orbit. The spiracles being somewhat oblique 
and transversely elongated. The branchial apertures increase in size from forwards backwards; 
the fifth, which is conspicuously larger than the rest, is placed immediately in advance of the 
anterior margin of the pectorals. 
The dorsal fins are of moderate development, higher than long, and superiorly concave. The 
spine at the anterior margin of the second dorsal is larger than that of the first dorsal. The 
anterior margin of the latter fin is nearly equidistant between the pupil and the anterior margin 
of the second dorsal, which, in its turn, is nearer the anterior margin of the first dorsal than 
the extremity of the caudal fin. The upper lobe of the caudal is sub-lanceolate, posteriorly 
rounded off; the lower lobe is much deeper, sub-triangular, and concave upon its inferior 
margin ; the origin of either lobe is even. A shallow caudal groove may be observed along 
tbe base of the upper lobe. The ventrals are small, appearing more like a marginal expansion 
of the ventral appendage than fins properly so called. They are rounded off exteriorly and 
linear posteriorly. The anterior portion of their insertion is nearer the extremity of the caudal 
