72 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



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 what- 

 ever below. Tlio inferior border is convex, with an emargination near the center. 

 (PI. 39, llgs. 7, S.) 



In the adult skull from Bering Island, which has been mounted and placed on 

 exliibition, the t(>eth tuv fixeil in the alveoli so that their entire lengtli and tlie pecul- 

 iarities of the l)asal portion can not be determined. In general form, however, 

 they resemble those of the preceding specimen very closely. The anterior teeth 

 are placed oblicjuely — that is, so that the anterior margins of the two teeth arc 

 nearer together than the posterior margins. The teeth are also somewhat inclini'd 

 forward. The posterior teeth are strongly inclined forward and a little outward. 



The anterior teeth are rather concave along the middle internally and convex 

 externalh'. The portion above the alveoli is quite smooth. 



The posterior teeth are moderately rugose above the alveoli. The wliitish 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 IS to 20 mm. thick. These teeth have an antero- 

 external angular enlargement of the cement, so that they are somewhat triangular 

 in horizontal section. (PI. 30, fig. 3; pi. 31, fig. 5.) 



The data available are insufficient to enable one to determine satisfactoi'ily 

 whether the teeth differ materially in size in tlie two sexes, but it appears probable 

 that they do not. 



SKELETON. 



While the skeleton of Berardius bairdii (PI. 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." 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.* 



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 secm-e the whole of the small tail bones." "^ The discrepancy here 

 shown can not be accomited 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. 1G+ =46+ . 



The number of thoracic vertebrsi 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 belongmg to the eleventh pair. This last is much shorter 



1 Trans. Zool. Soc. London, vol. 8, 1872, p. 223. 

 * Ost6ographie ties Oetac^s, p. 615, pi. 23 *". 

 c Trans. New Zealand Inst., vol. 10, 1878, p. 339. 



