1887.] of Animals commonly named Dinosauria. 169 



there is no important difference of plan in the pelvis between the 

 animals which have been referred to the order Stegosauria and those 

 referred to the order Ornithopoda ; and similarly, the plan v of 

 construction of the pelvis is essentially the same in the animals on 

 which have been founded the orders Sauropoda and Theropoda. But 

 there is as marked a difference between these two pelvic types as can 

 be found in any part of the animal kingdom. These resemblances 

 and differences are shown in the figures, which are copied from type 

 genera of Professor Marsh's four orders. 



The evidence concerning the penetration of air cells into the 

 vertebrae has been less fully brought forward. But in the known 

 genera which have been referred to the Stegosauria, the vertebras are 

 solid, and the like condition obtains in all the genera of Ornithopoda. 

 The genera in Professor Marsh's list which are thus united are 

 Stegosaurus, Diracodon, Omosaurus, Scelido#aurus, Acanthopholis, 

 Crataeoraus, Hylaeosaurus, and Polacanthus, with Camptonotus, 

 Laosaurus, Nanosaurus, Hypsilophodon, Iguanodon, Vectisaurus, 

 Hadrosaurus, Agathaumus and Cionodon. 



On the other hand, the precaudal vertebrae of Sauropoda are more 

 or less hollow. This hollo wness may amount to perfect excavation 

 which leaves only an external investing film with a longitudinal 

 median septum, or it may include a multitude of internal cells, or it 

 may be limited to a pair of shallow impressed pits on the sides of the 

 centrum. One of the characters by which Professor Marsh defines 

 the Theropoda is: "vertebras more or less cavernous." The animals 

 included in the group appear to differ greatly in this condition. I 

 have no evidence of presacral vertebrae of Megalosaurus being 

 chambered, and the chambered condition of the caudal vertebrae rests 

 upon a few specimens such as the types of Poikilopleuron. Professor 

 Cope mentions that the tissue of the sacral vertebrae of Laelaps is so 

 coarse as to resemble a mass of borings of the Teredo, but still the 

 demonstration of the pneumatic condition has not been made. Nor is 

 the evidence clearer with regard to Zanclodon. Professor Marsh 

 figures deep pits in the sides of the dorsal vertebrae of Creosaurus. In 

 Ceratosaurus, Marsh observes that all the presacral vertebrae are very 

 hollow, and this is also true of the anterior caudals. The same 

 condition is described in the cervical vertebrae of Labrosaurus, though 

 the external foramina are small, while the Cceluria, if included in 

 the order, would show a vertebral condition more perfectly pneumatic 

 than in any of the Sauropoda. Hence, as the chambered condition of 

 vertebrae is developed in most of the types of the group, it is possible 

 that its absence in genera in which it is unrecorded may be due to the 

 small size of the foramina having failed to indicate its existence, or to 

 the air-cells having been so slightly developed that they did not 

 penetrate the bones, as is the case with penguins among birds. But 



