The mandible of _stejnegeri_ is much broken in the region of the angle on
both sides, but otherwise complete. As compared with a mandible of an
adult _bidens_, 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 _stejnegeri_ is 140 mm. long, or scarcely more than in the
young specimen of _europæus_ from New Jersey, and exactly the same as in
the adult type-specimen of the latter species, as figured by Van Beneden
and Gervais. The alveolus lies entirely behind the symphysis, 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 _bidens_
and the portion of the posterior margin of the ramus which remains
indicates that the angle was strongly directed backward. (Pl. 11, fig. 4;
pl. 12, fig. 1.)