mabsh.J CLASSIFICATION OF DIXOSAURIA. 237 



The skulls of Aetosaurus and Belodou both show features character- 

 istic of some of the dinosaurs, especially of the Sauropoda, but these 

 features need not be discussed here. 



AFFINITIES WITH BIRDS. 



The relation of dinosaurs to birds, a subject of importance, must 

 also be postponed for another occasion. One point, however, may be 

 mentioned in this connection. The pelvic bones of all known birds, 

 living and extinct, except the genus Archaeopteryx, are coossified, 

 •while in all the known dinosaurs they are separate, excepting Gerato- 

 sanrus (rig. 04) and Ornithomimus. Again, all known adult birds, liv- 

 ing and extinct, with possibly the single exception of Archaeopteryx, 

 have the metatarsal bones firmly united (fig. 66), while all the Diuo- 

 sauria, except Ceratosaurus (fig. 65), have these bones separate. The 

 exception in each case brings the two classes near together at this point, 

 and their close affinity is thus rendered more than probable. 



These few facts will throw some light on the affinities of the reptiles 

 known as the Diuosauria, The problem is certainly one of much diffi- 

 culty, and the writer hopes soon to discuss it more fully elsewhere. 



PART V. 

 CLASSIFICATION OF DUSTOSAITRIA. 



In the present review of the dinosaurs the writer has confined him- 

 self mainly to the type specimens which he has described, but has 

 included with them other important remains where these were available 

 for investigation. The extensive collections iu the museum of Yale 

 University contain so many of the important type specimens now known 

 from America that they alone furnish an admirable basis for classifi- 

 cation, and it was mainly upon these that he first established the pres- 

 ent system, which has since been found to hold equally good for the 

 dinosaurs discovered elsewhere. In the further study of these reptiles 

 it was also necessary to examine both the European forms and those 

 from other parts of the world, and he has now studied nearly every 

 known specimen of importance. These investigations have enabled 

 him to make this classification more complete, and to bring it down to 

 the present time. 



Many attempts have been made to classify the dinosaurs, the first 

 being that of Hermann von Meyer in 1830. The name Diuosauria, 

 proposed for the group by Owen in 1839, has been generally accepted, 

 although not without opposition. Hseckel, Cope, and Huxley followed, 

 the last in 1869 proposing the name Ornithoscelida for the order, and 

 giving an admirable synopsis of what was then known of these strange 

 reptiles and their affinities. Since then, Hulke, Seeley, Lydekker, 

 Gaudry, Dollo, Baur, and others have added much to our knowledge 

 of these interesting animals. 



