_Lateral aspect_ (Pl. 8, figs. 1, 2).—The temporal fossæ are a little longer than the orbit in _europæus_, but a little shorter than the orbit in _bidens_; in the former the superior margin is flat or a little concave, rather than convex. The exoccipital extends in an angle farther forward in _europæus_, and the suture between it and the zygomatic is, in consequence, less nearly vertical than in _bidens_. The premaxillæ at the sides of the blowhole are nearly horizontal, so that their superior surface is little seen from this aspect, while in _bidens_ they slope downward, so that the whole of the superior surface is visible. The high maxillary ridge, situated behind the anteorbital notch, is very noticeable from this point of view, as it shuts off a considerable portion of the premaxillæ. The convex inferior outline of the beak and its great depth at the base are also salient peculiarities. _Ventral aspect_ (Pl. 5, figs. 1, 2).—The anterior ends of the palatine bones are bifurcated, the inner part being the smaller. The two bones make but a narrow angle with the median line, instead of a wide one, as in _bidens_, and the surface of the maxillæ between them is strongly convex instead of flat. This convexity is narrowed at both ends, or, in other words, is fusiform in shape. No similar conformation is found in _bidens_, in which the inferior basal area of the maxillæ is flat. In the young Atlantic City skull of _europæus_, the vomer is visible as a small, narrow, club-shaped piece, 68 mm. long. Anteriorly it joins the premaxillæ, which form a prominent ridge in the median line. On each side of this ridge is a wide and quite deep groove. As the beak is lacking in the adult North Long Branch skull, its peculiarities can not be made known. In the type-skull the form is the same as in the Atlantic City skull, but the vomer does not appear at all on the palate. In _bidens_ the shape of the inferior surface of the premaxillæ at the distal end is quite different. A very narrow groove runs parallel with and close to the median line and the whole surface external to it is more or less convex. MANDIBLE. The mandible of the Atlantic City specimen of _M. europæus_ resembles that of the type, as figured by Van Beneden and Gervais, in the shortness of the symphysis and in the position of the tooth, which is in advance of the posterior end of the symphysis. A number of differences, however, require consideration. (Pl. 11, figs. 3 and 6.)