10 



Annals of the Carnegie Museum. 



the present specimen the facet for the cervical rib is broken away, 

 thus giving to this region a somewhat different aspect. 



The centrum shown in Figs. 3 and 4 I regard as pertaining to the 

 last donsal. The posterior extremity is moderately concave, and the 

 anterior slightly so. The lateral cavities are deep, though not so pro- 

 nounced as in the cervical ; that on the left side is decidedly deeper 

 than the one on the right. The neural canal was much larger than in 

 the cervical and at about its middle there is a deep pit giving origin to 

 two small foramina which no doubt served for the transmission of 

 nutrient blood vessels to the interior of the bone. The vertebral cen- 



FlGS. 3 and 4. Centruiii of last ? dorsal seen from left side and above. (No. 

 578.) One half natural size. 



trum described by Marsh as a posterior dorsal and figured in plate XL. , 

 Figs. 4 and 5, of his Dinosaurs of North America, in reality pertained 

 to an anterior dorsal, as is evidenced by its strongly opisthoccelian 

 character and the more extended pleurocentral cavities, while the 

 dorsal centrum figured in the text as pertaining to Pleitroccelus was 

 from the mid-dorsal region, as is evidenced by its less decided opistho- 

 coelian nature and smaller lateral cavities. 



In Figs. 5 and 6 are shown lateral and superior views of a posterior 

 caudal centrum, pertaining to about the same region as that figured by 

 Marsh in plate XL., figs. 8 and 9, of his Dinosaurs of North America, 

 from a specimen found in the Potomac beds of Maryland. The pres- 

 ent specimen was found by Mr. Gilmore in the Atlantosaurus beds, on 

 Sheep Creek, Wyo., but in a different quarry from that which furnished 

 the dorsal and cervical centra figured al)0ve. 



