FOSSIL LIZARDS FROM WYOMING — GILMORE 75 



reason the extent of the underlying skull bones cannot be accurately 

 determined. The maxillary of the left side is complete and from end 

 to end has a length of 8.5 mm. The complete dental series of the 

 maxillary consists of 12 pleurodont, subcylindric teeth. The 

 premaxillary has eight teeth in the complete series, as in Peltosaurus. 

 The spine of the premaxillary is ornamented with three longitudi- 

 nal rows of osseous tubercles, the central row having the largest ossifi- 

 cations. The nasal region is covered with tubercles of varying sizes 

 and without definite arrangement. Those above the prefrontal are 

 the largest tubercles on this portion of the skull and form a distinct 

 row along the orbital border. Although the frontals are missing in 

 this specimen, it is quite evident that the prefrontal strongly laps 

 this bone and that its posterior termination reaches nearly to the cen- 

 ter of the orbit. 



Figure 32. — Anterior part of the skull of Exostinus serratus Cope (U.S.N.M .No. 16565), 

 viewed from left side: if, Dentary; /, prefrontal; mx, maxillary; na, nasal; 'pmx, pre- 

 maxillary. About three and one-half times natural size. 



The type ' on which this genus and species is based consists of the 

 frontals, left zygomatic, and a portion of the dentary with a few 

 teeth. The frontals are also covered with bony tubercles, a series 

 along each supraorbital border, longitudinal at the front, quadrate 

 at the back. A single median row separates them. On the posterior 

 end of the frontals, they are arranged in three transverse rows of 5, 

 4, and 3 tubercles, respectively. On the zygomatic there are two lon- 

 gitudinal rows of flat quadrangular tubercles. 



The incomplete dentary carries 14 teeth, and it appears that two or 

 more may be missing from the posterior end of the series. In the 

 article cited I stated that "the upper teeth [are] similar to the lower" ; 

 this is true only so far as both are pleui'odont, with subcylindric 

 shafts and simple crowns. The lower are more robust than the up- 

 per and their crowns project farther beyond the parapet of the jaw, 

 as clearly shown in figure 32. In this specimen there are nine teeth 



» Gilmore. C. W., Mem. Nat. Acad. Sci., vol. 22, p. 22, pi. 25, figs. 4-6, 1928. 



