260 Pi'of. 0. C. Marsh^JVew Jurassic Dinosaurs. 



aid in keeping the body balanced. Possibly this position was 

 assumed habitually by these ferocious biped reptiles, in lying in wait 

 for prey. 



The Hind Limbs. — Several restorations of the posterior limb of 

 Megalosaurus have been attempted, but the imperfect material at 

 hand was not sufficient to ensure entire success. In the restoration 

 of Allosaurus, given in Fig. 7, only the bones found together have 

 been placed in position. The relative proportions of the femur and 

 tibia are shown in this figure, and the general structure of the foot. 

 The astragalus and calcaneum are distinct from the tibia and fibula, 

 as in all the known Theropoda, although their coalescence has been 

 regarded as certain in some of the genera.' 



In the foot of Allosaurus fragilis, represented in Fig. 7, no tarsal 

 bones of the second row were found, although the adjoining bones 

 were nearly in their natural position. Whether the former were 

 imperfectly ossified, or lost, in this instance cannot be determined 

 with certainty, but there is evidence of the presence of these bones 

 in several other members of the group. In the present foot, there 

 were three functional digits. The metatarsals are very long, and 

 fitted closely to each other, especially at their upper ends. The 

 phalanges and claws were mostly found near the positions here 

 assigned to them. 



The specimens of Theropoda here first described, including the 

 type specimen of Ceratosauriis nasicornis, are from the Atlantosaurus 

 beds of the Upper Jurassic, in Colorado, where they were found by 

 Mr. M. P. Felch. The associated fossils are various Sauropoda, 

 Stegosauria, and Ormthopoda, together with Jurassic Mammals.^ 



Classification. 



The main characters of the order Theropoda and of the families 

 now known to belong to it, are as follows : — 



Order Theropoda. 

 Premaxillary bones with teeth. Anterior nares at end of skull. Large antorbital 

 opening. Veitebrae more or less hollow. Fore limbs very small ; limb bones 

 hollow. _ Feet digitigrade ; digits with prehensile claws. Pubes projecting down- 

 ward, with distal ends cobssified. 



(1.) Fa.mily Meffalosaufidce. Anterior vertebrae convexo-concave ; remaining verte- 

 bras bi-concave. Pubes slender. Astragalus with ascending process. 



Genera, Megalosav,rus [Poikilopleuron) , Allosaurus, Gxlosaurus, Creosaurus, 

 Dryptosaurus [Lcelaps). 

 (2.) Family Ceratosauridm. Horn on skull. Cervical vertebrae plano-concave, 

 remaining vertebrae bi-concave. Pubes slender. Pelvic bones coossified. Osseous 

 dermal plates. Astragalus with ascending process. 

 Genus, Ceratosaurus. 



^ Compsognathus is cited as an instance of this union, but in a careful study of the 

 original specimen in Munich, the writer found evidence that the astragalus is distinct, 

 although closely attached to the tibia. Baur lias since proved this conclusively 

 (Morpholog. Jahrbuch, viii.). In the Stegosauridm alone, among known Dinosaurs, 

 is the astragalus coossified with the tibia. This, however, is not a character of much 

 importance. 



^ The presence of various genera of Dinosaurs closely allied to these American 

 forms in essentially one horizon in the Isle of Wight, suggests that the beds in which 

 they occur are not "Wealden, as generally supposed, but J urassic. 



