_49599. Newport, Rhode Island._—Adult male. All sutures on superior surface of skull more or less anchylosed together. Mesirostral ossification and premaxillæ all on one level near apex of rostrum, but at extreme tip mesirostral lower, forming a narrow ridge with a deep groove on each side between it and premaxillæ. The same conformation repeated more posteriorly, but grooves deeper and wider, while mesirostral maintains the same level as premaxillæ. It widens suddenly here, forming a broad flat-topped mass, which is a little overlapped by the premaxillæ. The mass terminates suddenly somewhat behind middle of rostrum with a deep concavity placed obliquely. Basin in front of the nares and conformation of bones composing it as in two preceding skulls. Vomer at proximal end touching lower end of nasals, and nasal septum continued behind and above it as a low ridge, composed of the inner edges of the two nasal bones and reaching up to the nasal boss. Outer sides of premaxillæ near distal end deeply concave. Apex of rostrum rather blunt, deeper than wide opposite distal ends of maxillæ; all the bones anchylosed together, but some of the sutures indicated by grooves. Rudimentary alveolar groove nearly obsolete. (Pl. 17, fig. 2; pl. 19, fig. 2; pl. 21, figs. 1, 5.) Rami of mandible anchylosed together at symphysis, the suture indicated only by a groove. Teeth large, broadly conical and tapering at the tip. Root very short, rugose, conical and closed; diameter 29 _mm._ (Pl. 22, fig. 2; pl. 23, figs. 2, 3.) The dimensions of the several skulls are as follows: _Dimensions of ten skulls of Ziphius cavirostris (including the types of Z. grebnitzkii Stejneger and Z. semijunctus Cope)._ Column headings: A: 83991. Bering Island. _grebnitzkii._ B: 21248. Bering Island. _grebnitzkii._ C: 22874. Bering Island. _grebnitzkii._ D: 21246. Bering Island. _grebnitzkii._ E: 20993. Bering Island. Type _grebnitzkii_. F: 22069. Bering Island. _grebnitzkii._ G: 21245. Bering Island. _grebnitzkii._ H: 21975. Type _semijunctus_. I: 20971. Barnegat, N. J. Female, _cavirostris_. J: 49599. Newport, R. I. Male, _cavirostris_.