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 8ub-corru8;ated 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 off. 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 the 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, jerrated, 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. 



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 fni ; thirty-seven shields in the lateral series, and eight or nine between the pectorals and the ventrals. All the 

 shields more or less appro.ximated in their respective series. First dorsal shield united to the cephalic cuirass. 



Stn. — Aciptnser nudiroslris, Ayres, in Cal. Acad. Nat. Sc. I, 1854, 15. — Grd. in Proc. Acad. Nat. Sc. Fhilad. 

 VllI, 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. 

 acutirostris ; 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, sublanccolated, 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 iiict being stated merely 

 to show that the references to the present species have an imprint of authenticity. 



