

84 0. 0. Marsh — New Dinosaurian Reptiles. 



Ornithomimus velox, gen. et sp. nov. 



The high, degree of specialization in the reptiles above 

 described has a partial parallel in a small group of typical 

 Omithojpoda from the same horizon. Various specimens of 

 these, recently secured, represent a distinct genus and several 

 species. The most marked characters already determined are 

 manifest in the limbs and feet, and these have been selected for 

 description in the present notice. A typical example is shown 

 on Plate I, figures 1-3, which is the type specimen of the 

 species here described. 



On the distal part of the tibia represented in figure 1, the 

 astragalus is seen in place, with a very large ascending process, 

 larger than in any dinosaur hitherto known. The calcaneum 

 is also shown in position, but the slender fibula is absent. 

 This bone was complete, but of little functional value. The 

 tibia and all the larger limb bones were hollow, with thin 

 walls, as indicated in the section, figure 1, c. 



In figure 5, the corresponding parts of a young ostrich are 

 shown for comparison. The slender, incomplete fibula is in 

 place beside the tibia. The astragalus with its ascending pro- 

 cess, and the distinct calcaneum, are also shown in. position. 

 The almost exact correspondence of these different parts in 

 the bir4 and reptile will be manifest to every anatomist. 



The most striking feature of the foot belonging with the 

 reptilian tibia is shown in the metatarsals represented in figure 

 2, A. These are three in number, and are in the same position 

 as in life. They are the three functional metatarsals of the 

 typical Omithopoda and of Birds. The distal ends of these 

 bones correspond in size and relative position in the two groups, 

 but here, in the present specimen, the reptilian features cease, 

 and those of typical Birds replace them. In all the reptiles 

 known hitherto, and especially in Dinosaurs, the second, third, 

 and fourth metatarsals are prominent in front, at their proximal 

 ends, and the third is usually the largest and strongest. In 

 birds, the place of the third is taken above by the second and 

 fourth, the third being crowded backward, and very much dimin- 

 ished in size. 



This character is well shown in figure 6, which represents 

 the second, third, and fourth metatarsals of a young turkey, 

 with the tarsal bones absent. In the reptilian metatarsals seen 

 in figure 2, the same arrangement is shown, with the tarsals in 

 place. The second and fourth metatarsals have increased 

 much in size in the upper portion, and meet each other in 

 front. 



