OSTEOLOGY OF CARNIVOROUS DINOSAURS. 137 



In size the type of Orniihomimus tenuis is intermediate between 0. velox Marsh 

 and 0. alius Lambe. Resembling the latter more nearly in the more sudden con- 

 traction of the median portion of the shaft, but except for its very much smaller 

 size (being one-third smaller), this bone resembles the corresponding element in 

 Gorgosaurus more closely than it does any of the Orniihomimus metatarsals which 

 have been figured or with which it has been compared. When viewed from the 

 front the shaft is seen to have very little expansion toward the outer side, and the 

 presence of a decided transverse excavation just above the distal articulating sur- 

 face on the front are both features in which it differs from Orniihomimus and Stru- 

 thiomimus and in which it resembles Gorgosaurus. 



I am of the opinion that there is reason for considerable doubt to be cast on 

 the present generic assignment, and that eventually it will be found to pertain to 

 some other Upper Cretaceous theropod genus. 



ORNITHOMIMUS AFFINIS, new species. 



Allosaurus medius Marsh (part), Amer. Journ. Sci., ser. 3, vol. 35, 1888, p. 93. 



Dryosaurus grandis Lull, Md. Geol. Surv., Lower Cretaceous, 1911, pp. 204-206, pi. 19. figs. 6, 7; 

 pi. 20, figs. 1-4. 



Cotypes. — No. 5704, U.S.N.M., distal extremity of metatarsal II, right foot; 

 Cat. No. 5684, U.S.N.M., distal extremity of metatarsal III, right foot; Cat. No. 

 5453, U.S.N.M., and 6108, proximal phalanges, digit II, both pertain to left feet; 

 Cat. No. 5703, U.S.N.M., second phalanx, digit III, right foot; Cat. No. 8456, 

 U.S.N.M., second phalanx, digit IV, left foot; 6107, U.S.N.M., ungual phalanx, right 

 hind foot, astragalus, No. 5652, U.S.N.M. 



Type localities. — All of the cotypes, excepting No. 8456, U.S.N.M., collected 

 near Muirkirk, Prince Georges County, Maryland, by J. B, Hatcher in 1888. The 

 latter from Contee, Maryland, was collected by Arthur Bibbins. 



Horizon. — Arundel formation, Lower Cretaceous. 



In 1888 Marsh established the species Allosaurus medius on a number of sep- 

 arate bones, all of which, excepting a tooth, were subsequently referred by Lull to 

 the genus Dryosaurus. 



I now propose to remove all of the material mentioned by Lull, in his original 

 description of Dryosaurus grandis to the genus Orniihomimus, these to become the 

 cotypes of the new species Orniihomimus affinis. 



I have compared these cotypes with the homologous elements of the Orniih- 

 omimus skeleton, and with other Ornithomimid specimens in the American Museum 

 of Natural History from the Edmonton and Belly River formations, and find such 

 close resemblances as to leave no doubt of their generic identity. Mr. Barnum 

 Brown examined the typical specimens, and he concurs in my determination that 

 they represent an Ornithomimid dinosaur. 



The recognition of an Ornithomimid dinosaur in the Arundel fauna of Mary- 

 land comes naturally as a surprise, for prior to this time remains of the Ornitho- 

 mimidae have only been found in the Judith River, Belly River, Edmonton, Denver 

 and Lance formations of the Rocky Mountain region, all Upper Cretaceous, while 

 the Arundel has, on the best authority, been considered Lower Cretaceous in age. 

 This discovery, therefore, greatly extends the known geographical and geological 



