138 The Ottawa Naturalist. (November 



flattening- of the anterior and posterior borders takes place and 

 becomes more pronounced near the base of the crown, a slight 

 flattening of the sides of the teeth also becoming more decided in 

 the lower portion of the crown. The anterior carina passes grad- 

 ually to the inner side of the crown whilst the posterior one is well 

 over toward the outer side for the greater part of its length. 

 The posterior keel extends downward for the whole length of the 

 crown but the anterior one stops at about one-fourth the height 

 of the crown from its base. 



The anterior part of the external surface of the dentary of the 

 smaller specimen is rough, and exhibits a number of small fora- 

 mina, near its lower front margin, with others in a line at some 

 distance below and parallel to the alveolar border. In the larger 

 specimen a few openings of corresponding size are also apparent 

 near the anterior lower border of the dentary but the general surface 

 of the bone is smoother. In this specimen also a somewhat obscure 

 row of shallow depressions extends upward and backward in an 

 oblique curve (above e in figure i) across the dentary at about its 

 mid-length. This feature is suggested in the dentary of the smaller 

 specimen, but it is too indistinct to be spoken of with certainty. 

 The front portion of the surangular is striated as shewn in 



figure I. 



MEASUREMENTS. 



Of larger specimen, collected in 1884 (plate I). 



MM. 



Extreme length of left ramus of mandible . 970 



Greatest depth of same (approx. ) 227 



Length of dentary 905 



Depth of dentary at its mid-length, at a, figure i (approx. ) 185 



Thickness of ramus at mid-height anteriorly, at 6, figure lA 52 



Length of surangular above 490 



Thickness of surangular through (he ridge near its upper border, at 



r, figure i 33 



Thickness of surangular above the ridge, at c 23 



.. ,. below ,, ,, 14 



Height of surangular foramen 38 



Width of posterior portion of angular near its distal end, figure 4 50 



Width of same at g^ figure 4 30 



Thickness of same at ^ 33 



Transverse diameter of articular cotylus 112 



Thickness of ramus from upper surface of cotylus, at its mid-length, to 



lower surface of dentary 4 



