ART. 9 A NEW DINOSAUB FROM WYOMING GILMORE d 



indicated that the boundary of this opening on the posterior side 

 is formed by an outwardly directed process of the parietal joining 

 an inwardly directed process of the squamosal, as is usual in other 

 dinosaurian skulls. 



The bone structure of these dermal ossifications appears distinctive 

 of the Troodont dinosaurs, and on that account is worthy of de- 

 tailed description. Each of the sections from the supratemporal 

 area that are surmounted by a rounded node fractures downward 

 taperingly to more or less of a point. The bone fibers of these 

 broken surfaces concentrate at a focal point at this lower end, 

 which no doubt explains the reason for the similarity of the frac- 

 tures. A somewhat similar radiating structure was noted on the 

 broken surfaces of the dome mass before the pieces were cemented 

 together. This fact leads to the suggestion that the dome, after all, 

 may not be a thickening of the parietal and frontal bones, as for- 

 merly thought, but is a concentration of a series of dermal ossifica- 

 tions that have become fused, not only to one another but to the 

 underlying skull elements. Further evidence favoring such an in- 

 terpretation is found in Troodont skulls studied by Lambe,^ in which 

 he notes that the structure of the bone forming the dome is columnar 

 in section. 



On the left side of the specimen the squamosal and much of the 

 postfrontal are present, but they are so fully coalesced, not only with 

 one another but with the adjacent skull elements, that their extent 

 and limitations can no longer be determined. The squamosal is ex- 

 ceedingly massive and apparently forms the whole of the posterior 

 external angle of the skull. Its upper external surface is sparsely 

 covered with low, rounded tubercles of varying size, but below and 

 in front of these the bone surface is lumpy but otherwise smooth. 

 The upper surface of the postfrontal forms a narrow shelf along the 

 lateral base of the dome. Whether the squamosal also contributes to 

 the formation of this shelf can not be determined. The outer edge 

 is rounded, not raised as in T. validits. On the under side the 

 squamosal is cupped for the reception of the quadrate head, which 

 is missing in this specimen. Back of this cotylus a heavy, slightly 

 curved, bluntly pointed process represents the posterior overhang 

 of the squamosal. All of the skull elements, including a forward 

 portion of the postfrontal bone, are missing. The smooth but 

 pitted areas that form the roof of the orbital cavities are preserved 

 on the ventral side (pi. 3, fig. 2), and these accurately indicate the 

 position of the orbits. 



When the top of the orbital roof and the upper boundary of the 

 infratemporal fossa coincide on a horizontal line the upper part of 



= Trans. Roy. Soc. Canada, ser. 3, vol. 12, p. 24, 1918. 



