_Dorsal aspect_ (Pl. 2, figs. 1 and 2).—The premaxillæ are more depressed immediately in front of the blowhole than in _M. bidens_, which, with the prominence of the maxillary ridges, makes this whole region appear strongly concave. The blowhole is narrower absolutely and also relatively to the breadth of the expanded proximal ends of the premaxillæ, so that while in _bidens_ the breadth of the blowhole is much more than one-third the breadth across the proximal ends of the premaxillæ, in _europæus_ it is considerably less than a third. Both premaxillæ are much constricted on the sides of the blowhole and the effect is heightened by the greater expansion of the proximal ends of the former. These ends do not fit closely against the adjoining edge of the maxillæ as in _bidens_, but leave a transverse vacuity, or trough, which is especially noticeable in the type-skull. The anterior end of the malar bone occupies the bottom of the maxillary notch and a small portion of it is visible from above, while in _bidens_ it does not extend up into the notch at all from the inferior surface and is not visible from above. The posterior margin of the maxillæ is more squared in _europæus_ than in _bidens_. The margins of the beak, formed by the maxillæ, instead of being straight, are somewhat emarginate a little posterior to the middle of the length and somewhat convex anterior to it, which gives the contour of the beak, seen from above, a different shape from that of _bidens_. In the type-skull of _europæus_ the mesirostral ossification appears to be higher at the proximal end than the premaxillæ, and distally extends to the end of the beak. In _bidens_ it is lower than the premaxillæ and, in the Nantucket skull at least, ends anteriorly at the same point as the vomer, or, in other words, much behind the end of the beak. It would appear from the statements of Sir William Turner, Van Beneden and Gervais, Grieg, and others, that the mesirostral ossification never reaches the end of the beak in _bidens_, but it does in _grayi_, _haasti_, _densirostris_, and many fossil species, as well as in _europæus_.