26 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



In the Oregon skull of siejne(jeri, the breadth between the post-orbital processes 

 does not exceed the longtii from the occipital condyles to the maxillary notches. 

 The skull is, therefore, narrower in proportion to its length than in any other species 

 of the genus except hedori, as represented by the skull figured by Flower. This 

 skull was, however, that of a young individual. It is probable that in adults of 

 this species the skull is broader than in stejnegeri. 



In the latter species, again, tiie length of the brain-case, between the occipital 

 condyles and the maxillary notches, is just equal to the distance from the latter 

 point to the distal end of the maxillae, and the rostrum, including the premaxillse, 

 is much shorter than in other species of Mesoplodon, except Jiectori, as represented by 

 the young skull above mentioned. 



The foramen magnum is very small, being less in width than the condyle on 

 either side of it. In this respect it differs widely from Mdens and other species (as 

 far as can be ascertained from the figures available), except europseus, in which the 

 relative size is about the same. 



The supraoccipital rises vertically above each condyle to the very top of the 

 skull, being neither convex nor strongly bent forward as in other species, and espe- 

 cially Mdens. In the median line, however, while the occipital bone is flat imme- 

 atelv above the foramen magnum, it is deeply concave higher up and without a 

 metiian ridge. The outline of the occipital crest, viewed from behintl, is semicircular. 

 In all the foregoing characters the occipital region differs widely from that of bidens 

 and other species. The only close resemblance is found in the old skull of europseus 

 from Long Branch, New Jersey, and even here the sides of the occipital above are 

 far less prominent, their outline is much more convex, the occipital crest is angular, 

 and the median depression is less pronounced. 



Dorsal aspeet (PL 3, figs. 1, 2).— The most noticeable feature of the upper 

 surface of the skull is the large backward extension of the frontal plates of the 

 maxillfp, the free margins of which converge strongly. The outline of the ante- 

 orbital region is rounded. The anteorbital notch is a shallow emargination. Ante- 

 rior to this is a second still shallower emargination, the "pseudo-notch." The 

 margin between the two is much thickened, but does not form a distinct projection 

 or tubercle, as in bidens and other species. The superior orifices of the nares are 

 unsymmetrical as regards position, tiie left being somewhat in advance of the right. 

 The maxilhp are concave around the maxillary foramen, and external to this foramen 

 is an elongated ridge about as in europseus. The rostral portion of the maxillaj is 

 broad at the base but tapers more rapidly than in bidens. The margin is thick. 

 At the middle of the beak the outline of the maxillse at a lower level is visible from 

 above, which is not the case in bidens or europseus. The rostral portion of the 

 premaxillas is oblique proximally and vertical distally. Unlike bidens, these edges 

 are sharp throughout. The mesethmoid ends opposite the maxillary foramina. 

 Anterior to it is seen the concave upper surface of the vomer, which, however, 

 becomes flat distally. At about the middle of the beak the anterior end is clasped 

 by the posterior forked end of a " mesirostral " ossification, which has a convex 

 surface. This ossification begins proximally below the edges of the premaxillse, 

 but its surface rises gradually anteriorly, antl at the end of the beak it is much above 



