... 49 56 54 80 46 foramen magnum Length of [c]651 [ij]470 543 [i]464 ... 639 640 560 ... mandible Length of 237 241 162 ... ... 212 220 160 ... symphysis Greatest depth 106 114 92 102 116 110 97 95 ... of mandible [a] The size of the teeth makes it quite certain that it is an adult female. [b] End of beak broken off about 30 mm. from tip. [c] Right side. Add 31 mm. for breakage. [d] In median line. [e] At middle. [f] Between “suprafrontal processes of max.” [g] Grieg’s fig., p. 18, shows 44 mm. [h] From Grieg’s fig., p. 18. [i] “Length of ramus.” Length of mandible=699 mm. [j] In Trans. Roy. Soc. Edinburgh, vol. 26, 1872, p. 776. MESOPLODON DENSIROSTRIS (Blainville)? _Delphinus densirostris_ Blainville, Nouv. Dict. Hist. Nat., 2d ed., vol. 9, 1817, p. 178. _Ziphius seychellensis_ Gray, Zoöl. _Erebus and Terror_, 1846, p. 28. The skull of the specimen from Annisquam, Mass., (Pl. 1, fig. 2) is, I regret to say, in rather poor condition. It is broken in the left orbital region, and all the bones, especially those of the beak, are warped by weathering. The proximal extremity of the left premaxilla is lacking and also the tip of the beak. The skull is obviously that of a young animal, as all the sutures are open and the surface of the occipital condyles is pitted, owing to imperfect ossification. Although the dimensions of the skull, with a few exceptions, agree well with those of young specimens of _M. bidens_, as shown by the foregoing table (p. 8), certain differences stand out conspicuously. The most salient of these is the depth of the beak as a whole and the depth and shape of the rostral portion of the premaxillæ. The latter portion of the premaxillæ instead of being low, with a straight inferior margin, is very high, with the inferior margin strongly convex. At the middle of the beak the premaxillæ are higher than the maxillæ on which they rest. It is true that the shape of the beak varies greatly with age in _bidens_ and other species of _Mesoplodon_, but I do not find any evidence that such a change as is here indicated takes place in _bidens_. The form of the beak and of the rostral portion of the premaxillæ is that of _M. densirostris_. The beak is almost as broad at the base as in _bidens_, but the lateral free margin of the maxilla anterior to the anteorbital notch instead of continuing along the side of the beak nearly to the tip, as in _bidens_, ends at a point about 90 mm. in front of the line of the notch, beyond which the sides of the beak are vertical.