The Annisquam skeleton has nine dorsal vertebræ with their corresponding pairs of ribs. * * * The sternum of this specimen presents few points of interest. It consists of four pieces, the anterior-most of which is largest, slightly hollowed above, and correspondingly convex below. The three remaining pieces are nearly flat, with a deep median notch at the anterior and posterior border of each. The posterior piece evidently represents a fusion of the elements of two segments, as there are articular surfaces for two pairs of ribs. From the foregoing, it appears that the Annisquam specimen probably had one or two vertebræ less than _bidens_ or _europæus_, and that the sternum was somewhat differently shaped. The tooth, which is figured by Doctor Allen, is conical, compressed, 54 mm. long, 30 broad at the base, and resembles teeth of immature _bidens_. Although with such scant material it is not possible to determine satisfactorily the identity of this third species of _Mesoplodon_ in the North Atlantic, represented by the Annisquam specimen, I feel convinced that that specimen does not belong to _M. bidens_ and that there is a strong probability that it belongs to _M. densirostris_. It is true that the latter species has been found hitherto only in the Indian Ocean and about Australia, but we know so little about the distribution of the ziphioid whales that, in my opinion, that circumstance by itself should not be given very great weight. MESOPLODON EUROPÆUS (Gervais). _Dioplodon europæus_ Gervais, Zool. et Pal. franç., 1st ed., vol. 2, 1848-1852, p. 4; 2d ed., 1859, p. 289, pl. 40, figs. 3-6. _Dioplodon gervaisi_ Deslongchamps, Bull. Soc. Linn. Normandie, vol. 10, 1866, p. 177. _Neoziphius europæus_ Gray, Suppl. Cat. Seals and Whales Brit. Mus., 1871, p. 101. This species was based on a single specimen found floating in the English Channel about seventy years ago. An account of the circumstances under which it was found was given by Eugène Deslongchamps in 1866, as follows: The head, which forms the subject of this last note, was given to my father some twenty-five or thirty years ago by Mr. Abel Vautier, a merchant and armorer of our town, who died at Paris two years since.