148 The Ottawa Naturalist. [Feb. 



bone, which supplies the greater part of the eotylus for the 

 articulation of the quadrate, is stout and ascends in front against 

 the back surface of the coronoid process. 



The teeth are of the usual trachodont type and are in from 

 two to three rows in the grinding surface of the lower jaw. 

 A satisfactory examination of the inner enamelled surface of 

 the lower teeth has not been possible, but in two of the teeth 

 seen from the inner side, the margin appears to be smooth, or 

 nearly so. 



The edentulous part of the dentary is short and decurved 

 and is covered in front for a little more than half of its length 

 by the predentary. 



The front margin of the premaxillae, for a distance of 2\ 

 inches on each side of their median sutural union, is notched in 

 a regular manner. On each side of the dentate edge the margin 

 curves concavely upward and then merges into the extensive 

 depressed, lateral expansion. 



Superiorly, the predentary conforms to the shape of the 

 premaxillaries. -Its antero-lateral border rises on each side of 

 a sunken median portion which would receive the notched end 

 of the premaxillaries if the jaws were brought together. Postero- 

 laterallv, the predentary expands outward, producing a surface 

 which is concave above and conforms to the shape of the lower 

 surface of the lateral premaxillary expansion. This concave 

 surface terminates outwardly behind in a short pointed process 

 Antero-laterallv, the bone is excavated beneath the border 

 of the upper surface., The retreating lower median surface ends 

 posteriorlv in two processes, one on each side of the symphysis, 

 the anterior end of the dentaries being excavated to receive 

 them. These processes are longer than broad and thin vertically. 

 The predentarv is one-third the length of the dentary and one- 

 fourth that of the complete lower jaw. 



The skin impressions found w T ith the skeleton to which this 

 skull belongs are natural moulds and casts from the hinder part 

 of the body between the femur and the base of the tail. The im- 

 pressions are of non-imbricating, polygonal seales. smooth and 

 convex on the upper surface, and varying in diameter from 

 \ up to | of an inch, with an average breadth of about h of an 

 inch. In the considerable integumental area revealed, the scales 

 varv in size between the above limits without any definite pattern 

 arrangement. 



It may be found by further stud)- and comparison that the 

 Belly River species Trachodon selwyni, established by the writer 

 in 1902,* prineipallv on the evidence of teeth, is the same as 



Contributions to Canadian Palaeontololgy, vol 111 (quarto), pt. II. 



