THE LOWEK CHALK OP DOVEK. 441 



length is 5*3 inches, while the deepest part visible measures 1*2 

 inch, and the depth of the symphysis is about 0*8 inch. The man- 

 dible is partly overlain by the maxilla, -which hides the hinder part 

 of the alveolar border, about 2*5 inches being exposed to view ; and 

 this contains thirteen teeth, the anterior ones being a little shorter 

 than the others. Between the teeth there are spaces for about thir- 

 teen alveoli ; but only a few are visible. The outer surface is slightly 

 convex longitudinally, and more distinctly so in a direction at right 

 angles to its length. There is no groove along the lower border. 

 The largest tooth stands 025 inch above the alveolar margin, and 

 has a width of 0*1 inch. The crowns are compressed, the inner and 

 outer faces being separated by a moderately sharp cutting edge ; but 

 they do not appear to be so sharp or flat as in D. jpTdebotomus, Cope. 

 None of the mandibular teeth have the roots exposed ; but most pro- 

 bably they are long and cylindrical, like those of the maxilla. The 

 crowns which are best-preserved have a polished surface, orna- 

 mented with very faint traces of longitudinal striations. The 

 articular end of the jaw is shallow, and rises suddenly to the hinder 

 end of the dentary. The form of this part of the mandible is 

 supplied by the right ramus, which is to be seen on the under 

 surface of the specimen, displaced and thrown back to the hinder 

 part of the skuli. The suture between the articular and dentary 

 elements cannot be clearly traced, but is probably as shown in the 

 figure. The form of the hinder end of the articulare seems to indi- 

 cate that there was an angular element. The symphysis, when 

 seen from the side (fig. 1), forms almost a right angle with the 

 alveolar margin; seen from before (fig. 4) it resembles that of 

 Portheus, being nearly flat on the inner face, and convex externally ; 

 viewed from above it presents two facets, the one directed forwards 

 and slightly inwards, the other almost directly inwards, the junction 

 of the two facets being rounded. 



Maxilla. — The maxilla, in proportion to the mandible, is short 

 and deep ; its form will be best understood by reference to the 

 figure (fig. 1, mx). The greatest Width of this bone is towards the 

 front, in the region where, in all probability, it articulates with the 

 palatine. At this part the upper border forms a large rounded 

 process, and, passing backwards, curves rapidly downwards in a 

 regular sweep to its posterior end, which is thin and somewhat 

 broken. The anterior border articulates with the prsemaxilla, and 

 probably passes forward on its inner side as in other allied forms. 

 Where the two bones meet, the outer surface is depressed so as to 

 form a shallow groove. The alveolar border is convex from before 

 backwards ; and in it are implanted sixteen teeth ; between these 

 there are spaces for about sixteen alveoli, several of which are 

 visible. The extreme thinness of the hinder end of the bone 

 renders it very improbable that the teeth ever extended further 

 backwards. The roots of some of the teeth are exposed ; and these 

 are nearly cylindrical and hollow. Two or three young teeth are to 

 be seen projecting but little above the alveolar margin. The crowns 



