356 
U. S. P. R. R. EXP AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
somewhat nearer the mouth than the apex of the snout. The mouth is very large, provided 
with sub-papillar or sub-corrugated lips. The margin of the jaws is protected by a sub-corneous 
sheath,^exteriorly papillar, which on being removed leaves exposed numerous minute tentacles. 
These tentacles, or cilia, correspond to the papilla of the corneous sheath into which they are 
inserted. The anterior jaw corresponds to a vertical line drawn immediately behind the orbit. 
The pectoral fins are very large, broad, sub-lanceolated and posteriorly rounded olf. The 
ventrals are inserted opposite the twelfth lateral shield, and sub-truncated upon their posterior 
edge. The anal is much deeper than long upon its base, with its exterior edge sub-concave. 
The dorsal fin is higher anteriorly than long, sub-convex upon tlie latter edge, and superiorly 
concave ; the height of its posterior margin enters twice and a half time in the length of the 
base of the same fin. 
The periphery of the shields is very deeply indented, serrated, or digitated, especially sideways. 
Their spiny crest oftentimes exhibits additional small spines or points, either anteriorly or 
posteriorly. The stellated incrustations which are observed over the surface not covered by the 
shields, are likewise very prickly. 
The dorsal region is purplish or bluish black, whilst the abdominal region is whitish. 
List of specimens. 
Catal. 
No. 
No. of 
spec. 
Locality. 
When collected. 
Whence obtained. 
Nature of 
specimens. 
Collected by— 
1004 
i 
San Francisco, California.. 
1855 
Lieut. R. S. Williamson.. 
Alcoholic... 
Dr. John S. Newberry. 
1006 
i 
1857 
Dr. W. O. Ayres —. 
3. ACIPENSER MEDIROSTRIS, Ayres. 
Spec. Char. —Body fusiform in profile. Head rather stout; upper surface sub-convex, declivous, with a median, wide and 
shallow depression ; snout anteriorly rounded and abbreviated. Eleven dorsal shields from the occiput to the anterior margin 
of the dorsal fin ; thirty-seven shields in the lateral series, and eight or nine between the pectorals and the ventrals. All the 
shields more or less approximated in their respective series. First dorsal shield united to the cephalic cuirass. 
Syn. —Aclpenser medirostris, Ayres, in Cal. Acad. Nat. Sc. I, 1854, 15.— Grd. in Proc. Acad. Nat. Sc. Philad. 
VIII, 1856, 137. 
The head constitutes about the fifth of the total length. The eyes are rather small, sub_ 
circular, and situated much nearer the apex of the rostrum than the posterior edge of the opercle. 
The barbels being nearly equal in length and situated much nearer the apex of the rostrum 
than the mouth. The latter is very large, with a structure of the lips similar to those of A. 
acutiroslris; the anterior jaw, in its retracted position, corresponding to a vertical line drawn 
through the pupil. The insertion of the ventrals takes place opposite the fifteenth lateral shield, 
they being subtruncated upon their posterior edge. The base of the dorsal is equal in length 
to the height of its anterior margin ; it is superiorly convex, and quite low posteriorly. The 
anal is much deeper than long, sublanceolated, somewhat concave upon its outer edge. 
The periphery of the shields is entire, and the stellated incrustations which are observed over 
the intervening surface between the shield are likewise entire, or nearly so. 
The specimen which we have examined is a little short of two feet in total length, and we 
believe was submitted to Dr. Ayres’ inspection at San Francisco, This fact being stated merely 
to show that the references to the present species have an imprint of authenticity. 
