330 Principal Forms of the Dinosauria. 



type specimen is from Colorado, from a higher horizon in the 

 Jurassic than that of Megalosa/wus. Nearly every part of 

 the skeleton of this genus is now known, and the more impor- 

 tant portions have been described and figured by the author. 

 Creosaurus, also from the Jurassic, is an allied form, and 

 Dryjitosaurus, from the Cretaceous, is, perhaps, also closely 

 related. A very distinct form in the Jurassic is Z,ab?'osaurus, 

 described by the author, in 1879. It is known from detached 

 specimens only, but these, especially the jaws, edentulous in 

 front, show it to represent a distinct family. 



The most perfectly known of American Therojyoda, and by 

 far the most interesting, is the genus Ceratosaurus, founded 

 by the author, in 1884. This is the representative of a very 

 peculiar family, which differs in some important respects from 

 all other known Dinosaurs. The skull and nearly all the 

 various parts of the skeleton are known. When found, they 

 were entire, and in the position in which the animal died. 

 The skull and some of the more interesting parts of the skele- 

 ton have been figured by the author,' and all will soon be fully 

 described. 



The skull bears a large elevated horn-core on the median line 

 of the nasals. The cervical vertebrae differ in type from those 

 of any other known reptiles, having the centra plano-concave. 

 All behind the axis have the anterior end of each centrum 

 perfectly flat, while the posterior end is deeply cupped. This 

 genus, moreover, differs from all known Dinosaurs in having 

 the elements of the pelvis (ilium, pubis, and ischium) coos- 

 sified, as in all existing birds. The metatarsals, also, are firmly 

 united, as in birds. No representatives of the Ceratosauridw 

 are known in Europe. 



In conclusion, it may safely be said that the four great 

 groups of Dinosauria are each well represented both in Eu- 

 rope and America. Some of the families, also, of each order 

 have representatives in the two regions, and future discoveries 

 will doubtless prove that others occur in both. 



No genera common to the two continents are known with 

 certainty, although a few are so closely allied, that they cannot 

 be distinguished from each other by the fragmentary speci- 

 mens that now represent them. It must be remembered that 

 the great majority of genera have been named from portions 

 of skeletons, of which the skull was unknown, and until the lat- 

 ter is found, and definitely associated with the remains described, 

 the characters and affinities of the genus can be only a matter of 

 conjecture, more of less definite, in proportion to the perfec- 

 tion of the type specimens. 



