4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 79 



the occiput occupies a nearly horizontal plane. The occipital region 

 from a point somewhat above the position of the foramen magnum is 

 in a good state of preservation. At the center a flattened triangular 

 area that narrows ventrally represents the supraoccipital bone. Un- 

 fortunately, as in other parts of the skull, the sutures are all oblit- 

 erated. The smoothness of this central area is quite unlike the 

 deeply concave surface of the T. validus ^ skull, which has a low 

 sharp vertical ridge at the center. 



On either side lateral to this flattened central area are the wing- 

 like expanded processes of the paraoccipitals, which are directed 

 strongly outward and backward, their outer ends passing smoothly 

 into the posterior branch of the squamosals. 



ME1A.SUBEMENTS 



Mm. 



Greatest width of skull across squamosals 310 



Distance from center of orbital roof to rear of skull 244 



Greatest width of dome muss 275 



Greatest thickness about 180 



Troodon wyomingen^ may be at once distinguished from the 

 known species of the genus by its much larger size. Judging by the 

 few skull measurements obtainable, the type specimen is more than 

 twice the size of the largest T. validus cranium known from the Belly 

 River formation. It is further distinguished by the complete closure, 

 by dermal bones, of the supratemporal fossae, the smooth unsculp- 

 tured surface of the dome, and the simpler ornamentation of the 

 cranium throughout. From T. validus Lambe it differs further in 

 having a flattened supraoccipital area without a median ridge, and a 

 more steeply inclined parietal region posterior to the dome, the latter 

 making quite a difference in profile when viewed from the side, as is 

 clearly shown by comparing Figures 1 and 2, Plate 1. 



NOTES ON REFERRED SPECIMEN 



In Plate 4, Figures 1 and 2, are illustrated two incomplete bones, 

 U.S.N.M. No. 7806, that were collected from the Lance formation of 

 Niobrara County, Wyo., by J. B. Hatcher in 1890. It has long been 

 suspected that these fragmentary parts pertained to some undescribed 

 member of the Lance fauna, and on that account they have been 

 shown to practically all visiting paleontologists. Up to this time no 

 one would hazard a guess as to their origin. It was quite generally 

 agreed that they were dermal ossifications, one of which was orna- 

 mental in character. With the acquisition of the skull of Troodon 

 wyomingensis their origin seems to be explained. 



» Gilmore, Charles W.. Bull. No. 1, University of Alljerta Press, p. 21, 1924. 



