THE REPTILIA OF THE ARUNDEL 

 FORMATION 



BY 



RICHARD SWANN LULL 



The fossil reptiles of the Potomac, while not so abundant in numbers 

 or kinds as in the Morrison of our Western States, nevertheless compare 

 very closely with the latter, as nearly all of the Potomac genera and, in 

 some instances, very closely allied if not identical species are found in 

 the West. 



A striking similarity also prevails between the Potomac on the one 

 hand and the Wealden of Europe on the other, while one important 

 Maryland genus is reported from a lower horizon than the Wealden and 

 none from a higher level. 



The Potomac fauna is largely dino saurian, all of the sub-orders being 

 represented, in addition to which there is a crocodile, together with at 

 least one turtle and a ganoid fish. 



The Dinosaurs 



The carnivorous dinosaurs are represented by at least three species. 

 One, the common AUosaurus, the European representative of which is 

 Megalosaurus, may be recognized by feet and limb bones, vertebrae, and 

 teeth. This species, which has been named Allosaurus medius by Pro- 

 fessor 0. C. Marsh, was a creature of large size, comparing very favorably 

 with Allosaurus fragilis of the West, the estimated length of which is 

 34 feet. It walked entirely on the hind feet after the manner of its 

 kind, using the hands for grasping, and never for locomotion. The 

 teeth are sharp pointed, like recurved daggers, with finely serrated edges, 

 and often show a considerable degree of blunting through wear. 



