_Ziphius cavirostris_ Cuvier, Oss. foss., 2d ed., vol. 5, 1823, p. 353. _Hyperoödon gervaisii_ Duvernoy, Ann. Sci. Nat., ser. 3, Zoöl., vol. 5, 1851, p. 49. _Ziphius gervaisii_ Fischer, Nouv. Arch. Mus. Paris, vol. 3, 1867, p. 55. _Hyperoödon semi-junctus_ Cope, Proc. Acad. Nat. Sci. Phila., 1865, p. 15. _Ziphius semijunctus_ True, Proc. U. S. Nat. Mus., vol. 8, 1886, p. 586. _Ziphius grebnitzkii_ Stejneger, Proc. U. S. Nat. Mus., vol. 6, 1883, p. 77. It has not seemed to me necessary in the present connection to attempt to cite all the multitudinous names which have been given to this species, especially as those zoologists most competent to judge, including Van Beneden, Flower, and Turner, after detailed consideration, have concluded that but one species of _Ziphius_, or at most two species, exist at present.[35] Nearly all the skulls in European museums are assigned by the zoologists mentioned to _Z. cavirostris_ proper, but some doubt has been entertained regarding two or three European skulls, and one specimen from Argentina, described by Burmeister. These last-mentioned specimens have been thought to possibly represent a second species, _Z. gervaisii_. The principal characters of the latter are the narrow, flat premaxillæ, the lack of a prominent mesirostral ossification, and small teeth. From the large series of skulls in the National Museum, I am able to dispose of the doubt concerning _Z. gervaisii_. I find that wherever the characters above mentioned occur the sex (when known) is female. There is every reason, therefore, to believe that _Z. gervaisii_ is the female of _Z. cavirostris_.[36] I will return to this point again later. In 1865 Cope described a species from Charleston, South Carolina, under the name of _Hyperoödon semijunctus_. In 1886 I referred it to the genus _Ziphius_, but was in doubt as to its specific identity. I thought that it might represent _Z. gervaisii_, which is interesting in the present connection because the type-specimen was a female. In 1883 Dr. L. Stejneger described a species which he had discovered on Bering Island, Bering Sea, under the name of _Z. grebnitzkii_. Through the instrumentality of Doctor Stejneger and Governor Grebnitzki, the National Museum later received a large series of skulls from the same locality. The question of whether this species is identical with _Z. cavirostris_, or distinct, has caused me much study, and forms the principal subject of this chapter. The National Museum has at present the following material, which may be considered as certainly representing _Z. cavirostris_: 1. A complete skeleton and cast of an adult female, 19 feet 4 inches long, obtained at Barnegat City, New Jersey, October 3, 1883. Cat. No. 20971.