208 



The dental characters differ from those of Saurocephalus, as above 

 pointed out, and resemble more those of Saurodon leanus. The crowns of the 

 teeth are more exserted and slender. The inner face of the crown is more 

 convex than the outer; but there is no angle separating the two aspects. 

 The apex is moderately acute, and directed a little inward, owing to a slight 

 convexity of the external face. Enamel smooth. The alveoli are very close 

 together, and are probably only separated in their deeper portions. There 

 are forty-two teeth and alveoli in the maxillary bone. The superior condyle 

 is low, and its anterior border falls opposite to the last tooth, or the indented 

 surface which was occupied by the premaxillary bone. The more proximal 

 part of the maxillary curves inward and backward behind the position of the 

 premaxillary, more than in S. prognathus. The maxillary is a rather thin and 

 narrow bone, with a broad obtuse and thinned extremity. Its superior mar- 

 gin is marked with one or more acute ridges, which look as though it had a 

 contact with a large preorbital bone. The alveolar border is nearly straight. 



The dentary bone is remarkable for its straightness and laminar charac- 

 ter, and for the depth of the symphysis. The length of the latter is preserved, 

 while posteriorly to it the lower margin of the dentary is broken away. The 

 alveolar margin is slightly concave, and unites with the symphyseal at. an angle 

 of 65°. There are twenty-six teeth and alveolae, which grow a little larger 

 to the posterior extremity of the series; anteriorly, the alveoli are continent 

 externally, but, posteriori}', the septa are frequently complete, though thin. 

 In neither this bone nor the maxillary are to be found the foramina along the 

 bases of the teeth, characteristic of Saurocephalus or Sawocbn, as pointed 

 out by Harlan and Hays. 



Measurements. 



M. 



Length of the maxillary bone 0. 158 



Depth at the condyle 0.031 



Depth at the extremity (I. 022 



Length of the crown of a tooth c 0.0001 



Diameter of the crown at the base 0. 003S 



Length of the alveolar border of the dentary 0. 100 



Depth of the symphyseal border of the dentary 0.047 



Length of the opercular condyle 0. 01S 



Several osseous ventral rays accompany the cranial bones; they are prob- 

 ably interior in position, and are much more slender than the ventral spines 

 observed in I. anaides and /. prognathus. They are subquadrate in section, 

 not sculptured nor enameled; there is a shallow groove on the side. 



