AET. 16 FOSSIL EEPTILES FROM MONTANA GILMOEE 33 



The nearly vertical lateral surface between the orbits and the 

 external nares is covered by two large plates, the anterior one bend- 

 ing over to contribute to the dorsal surface. It also forms a part 

 of the posterior boundary of the narial opening. In Euoflocepha- 

 lus three plates cover this area. 



On the angle of the skull above each orbit is a large, blutly edged 

 scute that slightly overhangs the eye but to a lesser degree than in 

 Euoplocephalus. On each posterior external angle of the skull is 

 a large subtriangular spinelike scute that projects prominently 

 backward beyond the posterior border much as in Anhylosaurus. 

 Euoplocephalus has somewhat similar protuberances but sharper 

 edged and extending more upward. It is quite apparent that these 

 two scutes are missing from the posterior part of the Dyoflosaurus 

 skull figured by Parks.^^ 



The posterior end of the skull is in fair preservation and presents 

 a good idea of the arrangement of the occipital region, but many of 

 the palatial elements are entirely missing, or so badly crushed that 

 but little conception of its normal condition can be obtained. 



The occipital condyle is reniform in outline and directed backward 

 and downward. It seems quite apparent that the basal portions of 

 the exoccipitals participate in its formation much as they do in 

 Stegosaurus.^^ The condyle has a greatest transverse diameter of 

 54 mm., a greatest vertical diameter of 32 millimeters. The reni- 

 form shape of the condyle offers a striking contrast to the much 

 larger subspherical condyle in Palaeoscincus as shown in specimen 

 No. 11868, U.S.N.M. The foramen magnum is suboval in outline 

 and the supraoccipital border above it deeply notched. 



The basioccipital is about as long as it is broad. The ventral 

 surface between the condyle and the expanded anterior end is broad 

 and deeply concave with a shallow longitudinal depression occupying 

 the central area. The basioccipital processes are very short. The 

 exoccipitals extend outward nearly horizontal and with but little 

 angulation posteriorly. As mentioned above, their pedicles con- 

 tribute somewhat to the formation of the occipital condyle. At their 

 outer ends they join the quadrates by means of the paraoccipital 

 processes resting against a rugose area on the posterior sides of those 

 bones. They do not seem to be coalesced with the paraoccipital as 

 in Palaeoscincus rugosidens. 



The supraoccipital can not be differentiated. The quadrate is 

 relatively long, straight, and slender as compared with the more 

 plate-like element in the Palaeoscincus skull. The thin process that 

 extends forward and inward to meet the pterygoid is less than half 



81 Univ. Toronto Studies, No. 18, 1924, pi. 4, fig. 1. 



82 Gilmore, C. W., Bull. No. 89, U. S. Nat. Museum, 1914, p. 92, flg. 4. 



2601—30 3 



