bly applied to the opercular and surangular lbones, if they exist, 

 and a large foramen is continued from the concavity into the 

 remaining part of the dentary, as a tubular canal. Above the 

 foramen there originates a groove which runs parallel to the inner 

 alveolar border to the posterior edge of the sj^mphysis. The 

 latter is short, and scarcely distinguished from the other surfaces; 

 the attachment of the rami was evidently ligamentous and more 

 or less movable. The anterior alveolar portion of the ramus is 

 produced, so that the symphysis slopes backwards below. The 

 inferior border of the dentary bone is gently concave behind its 

 middle. It is throughout convex in the transverse direction. 



The external alveolar wall is an inch higher than the internal. 

 The inner portions of the septa are apparently subject to exfolia- 

 tion and subdivision in connection with the renewal of the teeth 

 as a groove which is continuous with the inner alveolar borders, 

 cuts them off from the other interior surface of the dentary bone. 

 The external face of the dentary is in general plane, but is vari- 

 ously excavated along its superior border. An inch below the 

 latter there extends a series of large foramina, each one of which 

 is situated opposite to an interalveolar septum. They are more 

 numerous anteriorly, a foramen being opposite each alveolus as 

 well, and each foramen is connected with the border by a shallow 

 groove. Similar foramina extend down the outer side of the 

 syrnphyseal border, and along the inferior border of the dentary 

 for two-thirds of its length. The same proportion of the external 

 face is obsoletely rugose through the presence of delicate lines of 

 growth. Such lines extend on the lower part of the interior face 

 obliquely upwards and backwards. 



There are alveolae for fifteen teeth in the dentary bone. Of 

 these only the second, third, fourth, fifth, twelfth, and fifteenth 

 contained teeth capable of functional use at the time the jaw was 

 inclosed in the lacustrine mud. Successional teeth occupy the 

 first, tenth, and twelfth, but no two teeth are in an identical stage 

 of protrusion. The section of the crown from and including the 

 fourth to the last is nearly equilaterally lenticular. Their surface 

 is smooth. 



