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. In the adult male from Centerville beach, California, only ten pairs of ribs are present, but as the tenth is quite as long as the ninth, there is little doubt that an eleventh pair was present originally. The eleventh thoracic vertebra, however, has transverse processes longer and more flattened at the free end than those of the tenth thoracic. It is possible, of course, that the real eleventh thoracic is lacking, and that this individual had thirteen lumbar vertebræ, but of this there is no positive evidence.