28 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



Ill the Aiiiiisquam skull, supposed to represent densirostris, although from a 

 young individual, the earbone is very much larger, especially the periotic, which is 

 also quite differently shaped. 



MANDIBLE. 



The miindible of stefnegen is much broken in the region of the angle on both 

 sides, but otherwise complete. As compared with a mandible of an adult hidens, 

 the most conspicuous differences are the shortness of the symphysis, the sharp 

 upward bend of the inferior margin anteriorly, and the large size of the alveolus. 

 The symphysis in the adult Oregon specimen of stcjnegeri is 140 mm. long, or scarcely 

 more than in the young specimen of eurofxus from New Jersey, and exactly the 

 same as in the adult type-specimen of the latter species, as figui'ed by Van Beneden 

 and Gervais. The alveolus lies entirely behind the symphj'sis, its anterior end 

 being 160 mm. from the anterior end of the jaw. It is 113 mm. long and 18 mm. 

 wide. The mandible is 62 mm. high at its middle point. The coronoid process is 

 more anteriorly situated than in iidcns and the portion of the posterior margin of 

 the ramus which remains indicates that the angle was strongly directed backward. 

 (PL 11, fig. 4; pi. 12, fig. 1.) 



TEETH. 



The teeth are remarkable for their size and form. They are somewhat more 

 than twice as broad as teeth of adult males of hidens, as shown by the figures of 

 Lankoster " and Grieg,'' and also a little longer. They are, in fact, probably broader 

 than, or at least as broad as, the teeth of any other species of Mesoplodon, not except- 

 ing hyardi. Sir William Turner remarks regarding a specimen of layardi examined 

 by him that "the breadth of the tooth, where it emerged from the alveolus, was 

 3^ inches." = lie does not state, however, whether the measurement was taken 

 along the top of the alveolus, at an angle with the transverse axis of the tooth, or 

 along the transverse axis itself. At all events, the teeth figured by Owen and 

 others are much less than 3^ inches broad. The teeth of adult europseus are only 

 2 inches broad, and of hidens, as already stated, 1^ inches broad. 



In stejnegeri (PI. 12, figs. 1-3) the portion of the tooth above the alveolus is 

 inclined slightly inward and backward, but the pointed tip curves outward so ^s 

 to be vertical. When extracted from the alveolus, the whole tooth is found to be 

 concave internally and convex externally. The posterior margin is convex and the 

 anterior sinuous, a slight convexity occurring on the portion which projects above 

 the alveolus. In this place the outer coating of cement is broken through, showing 

 the underhing dentine or osteo-dentine, which is somewhat corroded or absorbed. 

 This is particularly noticeable on the left tooth. 



The upper margin of the tooth is transverse, or nearly at right angles with the 

 anterior and posterior margins. The posterior angle is rounded and the anterior 

 raised into an acute point by the projection of the dentine as a distinct, sharp cusp. 



a Trans. Roy. Micr. Soc.,'vol. 15, 1867, pi. 5, figs. 1, 2. 



b Bergens Mus. Aarb., 1904, No. 3, p. 26, fig. 10. 



c Sci. F-esuIts of the Voy. of the Challenger, Zool., vol. 1, pt. 4, Bones of Cetacea, 1880, p. 13. 



f? 



