The Beaked Whales of the Family Ziphiidae / An Account of the Beaked Whales of the Family Ziphiidae in the Collection of the United States Museum...

by Frederick W. True

SKULL.

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.

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.)

In the type, the symphysis, as shown by Van Beneden and Gervais’ figure, plate 24, fig. 2a, is a little more than one-fifth the length of the mandible. The same relative proportion is found in the Atlantic City specimen, but, as the latter is a younger individual, one would expect the symphysis to be shorter. The figure of Van Beneden and Gervais gives the impression that in the type the end of the mandible is broken, and that, hence, the symphysis is shorter than it was originally. It will be observed that figures 2 and 2a do not agree as regards the length between the tooth and the end of the jaw, figure 2a showing a greater length. In figure 2, however, the jaw seems rather too long for the cranium, and if the greater length of the symphysis shown in figure 2a were introduced, it would certainly be so. The explanation of this discrepancy is not readily found; but one may be allowed to think that the symphysis is not so blunt in the type as is shown in figure 2.