The Atlantic City and Long Branch skulls also agree in numerous other
details of structure in addition to the foregoing, the more important of
which will now be mentioned. Unless otherwise stated, the type-skull, as
shown by Van Beneden and Gervais’ figures,[23] also presents the same
peculiarities in contrast with _M. bidens_.
_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_.
_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.