58 THE ROYAL SOCIETY OF CANADA 



arate element, has previously been observed in the Ceratopsia only in 

 Triferatops elatus, Marsh. In this connection Hatcher makes the fol- 

 lowing comment: "The specimen under consideration {Triceratops 

 elatus) furnishes the first example of a free coronoid yet observed in the 

 Ceratopsia, although this element is doubtless present in all the other 

 genera and species of the group, usually, however, being so completely 

 fused with the coronoid process of the dentary as to appear a portion 

 of that element, more especially in old individuals."^ 



The coronoid in the present specimen is much larger and more 

 prominent than that figured by Hatcher and Lull. It is applied to 

 the inner surface posteriorly of the coronoid process; it rises dis- 

 tinctly above the process and its posterior margin is as much as 20 mm. 

 to the rear. Viewed from the inner side its outline is rhomboidal 

 with the lower angle drawn out to a point and so twisted that the 

 internal surface becomes a sharp ridge directed intero-posteriorly. 

 Behind the ridge is a distinct concavity which slants forward inferiorly. 

 The extreme lower end where the bone joins the dentary is not clearly 

 shown ; its total length may be as great as 170 mm. The upper edge 

 is corrugated for the attachment of muscles. 



Measurements of Coronoid 



Total height 170 (?) mm. 



Greatest width horizontally 54 mm. 



Length of postero-superior edge 83 " 



Thickness near base, at least 19 



The surangiilar is a large and stout bone of irregular shape. 

 The upper portion is a vertical flange thinned anteriorly to fit like 

 a wedge between the coronoid and the coronoid process. The external 

 mandibular foramen is a prominent orifice directed down and back; 

 its boundary is formed in part by the posterior margin of the coronoid 

 process. The posterior margin of this flange-like portion of the 

 surangular turns inwards inferiorly, thus forming a concavity on the 

 inner surface of the bone into which the external mandibular foramen 

 opens. The external face of the fiange passes gradually into a ridge 

 sloping down and back and becoming the superior margin of the 

 thickened lower part of the bone. The external face of this lower 

 portion is slightly concave. The surangular overlaps the angular 

 both internally and externally. In addition to the external mandi- 

 bular foramen are four small foramina entering the surangular. The 

 relative size of these differs in the right and left bones; in fact, the 



1 U.S. Gaol. Sur., Monograph XLIX, pp. 137. 



