36 PEOCEEDINGS OP THE NATIONAL MUSEUM vol.77 



the outer side than in the tooth of No. 11892, U.S.N.M., as shown in 

 Figure 18A, where they are slightly visible from an inner view. 



3. A NEW HORNED DINOSAUR 



A fragmentary posterior portion of a ceratopsian frill is among 

 the specimens from the Two Medicine formation collected during 

 the summer of 1928. The presence of long horn-like processes on 

 the posterior border of the frill shows its affinities to lie within 

 the genus Styracosaurus^ but these differ to such an extent in form 

 and arrangement from those of Styracosaurus albertensis Lambe, 

 from the Belly River of Alberta; as to indicate a distinct species, for 

 which I now propose the name Styracosaw'us ovatus, the specific 

 name being suggested by the ovate character of the horn-like 

 processes. 



STYRACOSAURUS OVATUS, new species 

 Plate 10, Figure 2 



Type. — Cat. No. 11869, U.S.N.M., consists of the posterior por- 

 tion of the frill and numerous detached fragments. Collected by 

 George F. Sternberg, 1928. 



Type locality.— T. 37 N., R. 8 W., Milk River, Blackfeet Indian 

 Reservation, Glacier County, Mont. 



Horizon. — Two Medicine formation. Upper Cretaceous. 



A nearly entire posterior end of a median frill bone with its 

 attached processes is present. (See pi. 10, fig. 2.) This element in 

 the ceratopsian frill has been variously designated the parietal, 

 dermosupraoccipital, interparietal, and fused postfrontal. Stern- 

 berg ^* has recently attempted to show it to be the parietal in 

 styracosaurus^ but, although it appears to represent that bone in 

 Protoceratops, it certainly can not be the parietal in American 

 horned dinosaurs, as evidenced by the juvenile Brachyceratops and 

 other ceratopsian skulls in the National collections. I am unable 

 as yet to decide certainly on its homologies, and, as a matter of 

 expediency, shall continue to designate it the dermosupraoccipital. 



The outstanding peculiarity of the skull of Styracosaurus albert-, 

 ensis is the large horn-like processes that project outward and back- 

 ward from the posterior border of the frill. Somewhat similar 

 processes are present on the frill before me. The two processes 

 forming the hindermost pair lack their tips but it is quite evident 

 they were not as long as in the Canadian specimen. (Compare figs. 

 1 and 2, pi. 10.) Furthermore, these two horns are convergent as 

 opposed to the divergent processes in S. albertensis. It would seem 



=' Trans. Roy. Soc. Canada (ser. 3), vol. 21, 1921, pp. 135-143, pis. 1, 2, and 3. 



