II. 



)ISCOVERY OF REMAINS OF ASTRODON (PLEUROCCE- 

 LUS) IN THE ATLANTOSAURUS 15EDS OF 

 WVOMINCr. 



IW 



U. IIaiciii'-K. 



While engaged during the season of 1901 in collecting dinosaur 

 remains in the Atlantosaurus beds on Sheep Creek, Albany Co., Wyo- 

 ming, Mr. C. W. Gilmore discovered two vertebral centra (No. 578), 

 ■which I am unable to distinguish either generically or specifically from 

 those described and figured by the late Professor Marsh as pertaining 

 to riciirpccvlus nanus, which, as will be shown later, should l)e re- 

 garded as a svnonym of Astroi/on Jolinsfoni Leidy. 



Figs. I and 2. Cervical centrum of Astrodon johnstoni Leidy, .seen from left 

 side and above ; one half natural .size. (No. 578.) 



One of these centra, lateral and superior views of which are shown 

 in Figs. I and 2, I regard as pertaining to a posterior cervical. Its 

 sides are deeply excavated in such manner that the body of the cen- 

 trum is reduced throughout its middle region to superior and inferior 

 horizontal plates connected by a thin median vertical lamina. The 

 neural canal was small and much constricted medially. The centrum 

 is strongly opisthocoelous and the transverse diameter is greater than 

 the perpendicular. It agrees almost perfectly in size and general 

 characters with the cervical centrum of Astfodon (^P/ei/roccehts) nanus 

 figured by Marsh in his Dino.saurs of North America', except that in 



1 Sixteenth Ann. Rep. U. S. G. S., Pt. i, PI. XL. 



1) 



