The margin of the maxilla immediately anterior to the anteorbital notch is a little damaged, but there was apparently no strong tubercle at this point, and the surface of the maxilla, though convex, is not raised into a distinct ridge. In a young skull, however, one would not expect to find a high ridge. The palatines are visible from above, which is not the case in _bidens_. The maxillary foramen is situated a little in advance of the premaxillary foramen and is directed forward, and, as Dr. Glover M. Allen has pointed out, connects with a broad groove which runs forward along the triangular, horizontal portion of the maxilla at the base of the beak. The maxillæ are much broader behind the notch than in _bidens_, and the anterior end of the malar forms the bottom of the notch. The premaxillæ are noticeably constricted immediately in front of the premaxillary foramina, and the expanded portion just behind these foramina is nearly horizontal, with a low transverse ridge near the middle. The proximal end of the premaxillæ is nearly vertical. The anterior nares are noticeably small. The foramen magnum is large, with a trifoliate outline (Pl. 10, fig. 2). The palate at the proximal end presents a median ridge with a narrow groove on each side. The palatines extend as a broad band much beyond the pterygoids anteriorly. The vomer is visible below for a space of 142 mm. near the end of the beak. A very small piece is also visible at the base of the beak, between the palatines and pterygoids. The inferior surface of the pterygoids is convex on the side adjoining the lateral free margin (Pl. 4, fig. 2). This skull is peculiar in that there is no very distinct basirostral groove and that the basirostral ridge, as already stated, extends forward only about 90 mm. Below this ridge is a shallow broad groove which narrows rapidly forward and can be traced to the extremity of the beak, where it broadens out somewhat (Pl. 7, fig. 2). While this skull agrees in size and in many of its proportions with similar skulls of _M. bidens_, it differs from that species and agrees with _M. densirostris_ in the breadth across the anteorbital region, in the depth of the beak and its shape at the base, in the shape of the premaxillæ both distally and proximally, in the direction of the maxillary foramen, and the shape of the maxillary bone in front of the same, in the occupation of the base of the maxillary notch by the anterior end of the malar, in the absence of any distinct maxillary ridge above the notch, in the forward extension of the palatines, and in the shape of the foramen magnum. Flower states that there is a deep basirostral groove in _M. densirostris_,[16] but neither the figure in Gervais’ Zoologie et Paleontologie Française,[17] nor that in Van Beneden and Gervais’ Ostéographie des Cétacés,[18] shows such a groove. The conformation of the base of the rostrum appears to be about the same as in the Annisquam skull.