3. A young female, 12 feet 2 inches long, stranded at Annisquam, Massachusetts, August, 1898, and recorded by the late Alpheus Hyatt.[4] The skeleton is in the museum of the Boston Society of Natural History. 4. An adult female, said by fishermen who measured it to have been 22 feet long, entangled in pound nets at North Long Branch, New Jersey, July 22, 1905, and recorded by Dr. Glover M. Allen.[5] The cranium of this individual is preserved in the Museum of Comparative Zoölogy. The rostrum and mandible, which were originally obtained, were afterwards destroyed by accident. I have examined all this material. Writers who have had occasion to mention these four specimens thus far have referred them tacitly to _Mesoplodon bidens_ (Sowerby), but, after a careful study of them, I have ascertained that while the Nantucket specimen belongs to that species, the Atlantic City and Long Branch specimens represent _Mesoplodon europæus_ (Gervais). This is a very interesting discovery, because the latter species has been known hitherto only from a single skull, and its validity has been frequently questioned. The Annisquam specimen, as will be seen later, presents characters which appear to ally it to _M. densirostris_. MESOPLODON BIDENS (Sowerby). _Physeter bidens_ Sowerby, British Miscell., 1804, p. 1; Trans. Linn. Soc. London, vol. 7, 1804, p. 310. _Delphinus sowerbensis_ Blainville, Nouv. Dict. Hist. Nat., 2d ed., vol. 9, 1817, p. 177. _Delphinus sowerbyi_ Desmarest, Mammalogie, pt. 2, 1822, p. 521. The only specimen from the Atlantic coast of the United States which can with certainty be referred to this species is the one from Nantucket mentioned on page 3. Prof. L. Agassiz’s original notice of it is so brief that it is quoted in full below: Professor Agassiz also brought to the notice of the Society the discovery of a Cetacean, new to America. The skull was exhibited, and its peculiar features pointed out. It was obtained on the coast of Nantucket by Messrs. H. M. and S. C. Martin, of Roxbury. It belonged to the genus _Mesoplodon_, as characterized by Gervais, and ought to be separated from the fossil _Ziphius_, described by Cuvier. Professor Agassiz, however, questioned whether _Mesoplodon_ was not identical with _Delphinorhynchus_, previously described by De Blainville. The specimen found at Nantucket measured 16 feet in length.[6] SKULL.