REPTILIA OF KIETLAND FORMATION GILMORE 



175 



The surface of the carapace is undulating, and outside the verte- 

 bral areas it is ornamented by a series of low, round-topped bosses 

 and ridges. These are without regular arrangement and rather 

 sparsely placed. Vertebral areas except first and fifth are smooth, 

 these two being slightly roughened by low-lying elevations of ir- 

 regular shape and size. There is indication of a low median keel 



along the middle of the car- 

 apace, which becomes more 

 apparent toward the poste- 

 rior end. (PI. 16.) 



The scutal areas are dis- 

 tinctly marked on the shell 

 and give the most complete 

 information as to the ar- 

 rangement of the scutes in 

 this genus of any specimen 

 yet obtained. The abbrevi- 

 ation of the front of the 

 carapace has resulted in 

 greatly reducing the size of 

 the nuchal scute, which is 

 very narrow anteroposteri- 

 o r 1 y, measuring 4 mm, 

 whereas its width is 33 mm. 

 This is the first time the 

 presence of this scute has 

 been recognized in this 

 genus. Hay (1908, p. 96) 

 thought it to be absent in T . insilens, and this region was not pre- 

 served in the type of T. raplens. U.S.N.M. no. 8074, from the Lance 

 formation of Wyoming, which is referred to T. insilens Hay, dis- 

 tinctly shows a large nuchal present. 



Takle 3. — Comparative measurements of vertebrals of type specimens of two 



species of Tliescelus 



FiGUKE 11. — Carapace of Thescelus hemisphcrica. 

 Type, U.S.N.M. no. 12818, mi. Nuchal scute: 

 su.sc, supracaudal scute ; VI, V5, vertebrals 

 1 and 5, respectively. One-sixth natural 

 size. 



