186 Systematic Paleontology 



Occurrence. — Aeundel Formation. Near Muirkirk;, Prince George's 

 County. 



Collections. — U. S. jSTational Museum, Goucher College. 



Creosaurus potens sp. nov. 

 Plate XIV, Fig. 4 



Description. — ^The type specimen is a vertebral centrum (Ko. 3049, U. 

 S. JSTational Museum) from the ferruginous conglomerate of Washington, 

 D. C, which seems to represent a theropod dinosaur otherwise unrecog- 

 nized in the Arundel formation. 



The vertebra (fig. 3), evidently a posterior presacral, is of peculiar 

 proportions ; nearly as deep as long, and strongly compressed laterally, 

 the lower surface forming a distinct keel, which is nearly straight in 

 profile. The neural canal is broad, though somewhat constricted in the 

 middle of the centrum. 



The vertebra difl^ers materially from those of Allosaurus in lacking 

 the decided constriction in the middle and in the presence of the keel. 

 It resembles most nearly the vertebrae belonging to the type of Creosaurus 

 atrox (ISTo. 1890, Yale Museum), not, however, the one figured by Marsh 

 as Creosaurus.^ 



The vertebra in question is much larger than those of the type of 

 G. atrox, but the latter show the same compressed form, though with a 

 less straight ventral outline. 



The present vertebra is slightly opisthoccelous and its dimensions are 



as follows: 



Length 140.0 mm. 



Depth of centrum 128.0 mm. 



Width anterior face 98.5 mm. 



Width posterior face 97.0 mm. 



Least diameter of centrum 78.0 mm. 



This vertebra represents by far the largest carnivore known from the 

 Arundel formation. 



^ Marsh, 16th Ann. Rept. U. S. Geol. Survey, pt. i, 1896, pi. xii, figs. 5, 6. 



