No. 49726.—St. George Island, Alaska; female, adult. Anterior tooth conical, with the tip blunt, having been so much abraded that the dentine does not extend beyond the coating of cement. The tip measures 26 by 19 mm. The external and internal surfaces of the tooth are about equally convex and somewhat rugose without distinct furrows. The root is thicker than the remainder of the tooth and very rugose. It is entirely closed below, and the inferior outline is convex. Posterior tooth much compressed, conical above the root, nearly flat internally and slightly convex externally. Cement coating very thick and extending to within about 5 mm. of the dentine apex, which latter is acute and very slightly curved inward and backward. The root is very unsymmetrical, the posterior portion being much longer than the anterior. The surface is very rugose, and there is no opening whatever below. The inferior border is convex, with an emargination near the center. ([Pl. 39], figs. 7, 8.)
In the adult skull from Bering Island, which has been mounted and placed on exhibition, the teeth are fixed in the alveoli so that their entire length and the peculiarities of the basal portion can not be determined. In general form, however, they resemble those of the preceding specimen very closely. The anterior teeth are placed obliquely—that is, so that the anterior margins of the two teeth are nearer together than the posterior margins. The teeth are also somewhat inclined forward. The posterior teeth are strongly inclined forward and a little outward.
The anterior teeth are rather concave along the middle internally and convex externally. The portion above the alveoli is quite smooth.
The posterior teeth are moderately rugose above the alveoli. The whitish tips of denture are conical, compressed, and rather acute. They extend 6 mm. above the denture, and are 11 mm. long at their base, and 6 mm. thick.
The anterior teeth protrude about 45 mm. above the alveolus (internally); their base at the alveolus is from 73 to 76 mm. long, and from 33 to 35 mm. thick. The posterior teeth extend about 18 mm. above the alveoli (measured vertically from the alveolus), and the base of the visible portion (measured along the alveolus) is from 30 to 34 mm. long and from 18 to 20 mm. thick. These teeth have an antero-external angular enlargement of the cement, so that they are somewhat triangular in horizontal section. ([Pl. 30], fig. 3; [pl. 31], fig. 5.)
The data available are insufficient to enable one to determine satisfactorily whether the teeth differ materially in size in the two sexes, but it appears probable that they do not.
SKELETON.
While the skeleton of Berardius bairdii ([Pl. 42], fig. 4) resembles that of B. arnuxii very closely in most particulars, it presents differences which may properly be regarded as specific. The vertebral formula of B. arnuxii as given by Flower is as follows: C. 7, Th. 10, L. 12, Ca. 19 = 48.[58] The same formula is given for another specimen of B. arnuxii by Van Beneden and Gervais, except that the caudals are 17, two being apparently lacking.[59]
Doctor Hector, however, gives a different formula for a third specimen of this species, namely, C. 7, Th. 10, L. 13, Ca. 17 = 47. He remarks that “extreme care was taken to secure the whole of the small tail bones.”[60] The discrepancy here shown can not be accounted for at present, but, at all events, none of the formulas of B. arnuxii corresponds to that of B. bairdii, as derived from the three skeletons in the National Museum, namely, C. 7, Th. 11, L. 12, Ca. 16+ = 46+.
The number of thoracic vertebræ can be determined positively from the youngish male from St. George Island (Cat. No. 49727), in which ten pairs of ribs are present, together with one rib belonging to the eleventh pair. This last is much shorter than the tenth pair, and there can be no doubt that it really belongs to a terminal pair. In this skeleton the transverse processes of the eleventh thoracic vertebra are thick at the free end like those of the tenth thoracic vertebra.