ART. 16 FOSSIL REPTILES FROM MONTANA GILMOKE 7 



being a posterior extension of the premaxillae. The most striking 

 feature of these bones is the development of a vertical plate that 

 extends downward and divides the mouth longitudinally. This plate 

 anteriorly extends below the level of the tooth rows. In the speci- 

 men under consideration the greater part of this plate is missing, 

 but is completely preserved in the type of Edmontonia longiceps and 

 has been described in detail by Sternberg/ who says : " This plate 

 seems to be a development of the fused premaxillae." In this, how- 

 ever, I think he is mistaken; for in specimen No. 11868 this ridged 

 plate certainly develops on the prevomers as shown in Figure 2. 

 The purpose of this longitudinal plate is as yet unexplained, but 

 that it had a function there can be no doubt. A suggested similarity 

 is found in the palate of Troodon validus, but in that genus it con- 

 sists only of a pointed pendant ^ process. 



The palatines as distinct bones can not be differentiated in this 

 skull. It is presumed, however, that they form the median bar 

 of bone which separates the internal nares. That they probably 

 form the posterior boundary of the nares is indicated in the type of 

 Edfnontonia longiceps, where Sternberg was able to trace out a part 

 of the palatine-pterygoid suture. In the present skull all trace of 

 this suture has been obliterated. If correct in the determination of 

 these bones, the palatines form a considerable portion of the verti- 

 cal plate which divides the mouth cavity. Anteriorly they join the 

 prevomers, apparently intercalated between slender posteriorly 

 directed processes of those bones. 



The pterygoid bones, as in nearly all of the armored Dinosauria, 

 are greatly shortened antero-posteriorly. Each element may be 

 said to consist of three plates of bone, a rather narrow wing that 

 extends backward and outward and joins the quadrate, further in 

 front a nearly vertical lamina that extends forward to articulate 

 with the ectopterygoids^ and at the junction of the two processes 

 mentioned above a heavier vertical plate extends transversely to 

 meet its counterpart of the opposite side on the median line. At 

 their junction the bone swells out into a truncated triangular process 

 that projects downward considerably below the rest of the bone. A 

 median septa continues forward and upward from this process to 

 meet the palatines. On either side of this septa the pterygoids are 

 hollowed out. The sutural contact with the ectopterygoids seem to 

 be as indicated in Figure 2, but I have some misgivings as to whether 

 they are fractures or true sutures. 



■^ Trans. Roy. Soc. Canada, Art. 3, Vol. 22, 1928, pp. 99-100. 

 8 Gilmore, C. W., Univ. of Alberta, Bull. No. 1, 1924, pi. 5. 



