A number of rudimentary teeth in addition to the large terminal pair have been noted in the Aresquiers, Buenos Ayres, and perhaps other specimens, and two such teeth were found in the mandible of the Barnegat specimen, behind the large pair. One of these rudimentary teeth has been preserved. It is cylindrical and moderately curved. The length is 16 mm. and the diameter 2 mm. The whole tooth, with the exception of the extreme tip, is thickly coated with cement. The root is closed and the crown acute and apparently abraded by use. (Pl. 38, fig. 5.) Returning now to the question of the validity of _grebnitzkii_ as a species, I would say that after comparing the measurements of the Bering Island skulls with those of the Atlantic coast specimens, and comparing the skulls themselves, I have been unable to find any constant difference of importance, except the size and form of the periotic bone. As the earbones are lacking from many of the skulls, the series available for comparison is small. As compared with the Atlantic coast specimens, the anterior portion of the periotic bone in _grebnitzkii_ is larger, broader, and more rectangular in outline when viewed from below. I observe, however, that the absolute size and outline of the periotic vary considerably in the different specimens of _grebnitzkii_ without relation to age. The same appears to be true of _cavirostris_, but comparing the two series of skulls as a whole it appears to be true that the anterior mass of the periotic is larger in _grebnitzkii_. I do not think, however, that the latter species should be kept distinct on this account alone, at least until the character has been confirmed, and perhaps strengthened by others, through the examination of a larger series of specimens. SKELETON OF ZIPHIUS FROM BERING ISLAND. The Museum collection contains an incomplete skeleton of a very young individual, Cat. No. 22875, which was received from Bering Island with the skulls of _Z. grebnitzkii_, but does not belong to any one of them. Whether it really represents that species is, therefore, uncertain, but such is probably the case. The length of the vertebral column, consisting of 45 vertebræ, without interspaces, is 9 feet 2 inches. The vertebral formula is as follows: C. 7; Th. 10; L. 10; Ca. 18 (+1?) = 45 (+1?). This is the same as in the type of _semijunctus_ so far as the cervicals, thoracics, and lumbars are concerned, and the probable total is the same. In their general characters these vertebræ agree with those of the skeletons already described, but they present a number of differences as well. On account of immaturity the processes are even less developed than in _semijunctus_. All the epiphyses are free, and in the third to the seventh thoracic vertebræ the neural arch and spine are separate from the centrum. The centra are very short in proportion to their width.