307 



by a concave upper border, a convex anterior border, a short, oblique, poste- 

 rior border, and a convex lower border. The surface is concave longitu- 

 dinally, and is convex transversely in front and behind, and concave in the 

 middle. 



The inner surface (Fig. 8) is flat transversely, slightly convex longitudin- 

 ally, and with the fore and back borders prominent. It is moderately stri- 

 ated in the length, and at its upper part presents a symphysial bevel, extend- 

 ing the length of the beaked portion of the bone. 



The oral surface (Fig. 6) on the beak is concave fore and aft, and at the 

 back half of the bone forms a lozenge-like plane sloping inwardly, and having 

 the outer border elevated. The sloping plane exhibits at its fore part inter- 

 nally a large cordiforni dental area, with the notch at the base of the beak. 

 Externally to this area, near the fore part of the crest defining the outer part 

 of the sloping plane, there is a second much smaller elliptical dental area. 

 These two areas are separated by a groove, widening forward upon the oral 

 surface of the beak, where it presents a third dental area. This is the third 

 in size, is oval in form, and is situated just in advance of the outer part of .the 

 largest dental area. 



A fourth area, smaller than the others, occupies the back extremity of the 

 symphysial bevel to the inner side of the anterior part of the largest dental 

 area. The dental column which forms this fourth area produces the prom- 

 inent ridge defining the inner surface of the ramus mandibuli posteriorly. 



Beside these dental areas, two or three others are observed at the end of 

 the beak. One of them curves from the symphysis outward and backward on 

 the outer edge of the point of the beak. Another smaller oval one is situated 

 at the edge of the symphysis behind the commencement of the former. In 

 one specimen a still smaller oval area is situated just behind the outer end of 

 the curved area, but in the other specimens it appears not to be distinct from 

 the latter. 



The dental areas in the fossils appear as depressed and decomposed, 

 friable, white, chalky tracts, with harder calcigerous tubules of the vaso- 

 dentiue projecting from the surfaces. The tubercular eminences originally 

 occupying the position of the areas and terminating the dental columns 

 have disappeared, leaving depressed surfaces. The vaso-dentiual columns 

 corresponding with the areas on the triturating surface are visible at the 

 posterior-inferior extremity of the mandibles, as seen in Fig. 9. 



