326 Principal Forms of the Dmosauria. 



Owen, 1841, is the earliest, and must be retain. d. The 

 remains on which this genus was based are from tSe Great 

 Oolite, or Middle Jurassic. Cardiodon, Owen, 1845, : s from 

 nearly the same horizon, and there appears no evidence that 

 the two forms are not identical. Pelorosaurus, Mantell, 1850, 

 is from the Wealden, and may be distinct, but, at presen., the 

 proof is wanting. Oplosaurus, Gervais, 1852, also from the 

 Wealden of England, cannot well be separated from Peloro- 

 saurus. Gigantosaurus, Seeley, 1869, from the Kimmeridge 

 of the Upper Jurassic, may prove to be different from the 

 above, but the type specimens alone do not indicate it. Boih- 

 ?*iospondylus, Owen, 1875, is also from the Kimmeridge, 

 and, although the type specimen pertains to a very young, if 

 not foetal individual, it seems to be distinct, and may be nearly 

 allied to the American genus Pleurocmhis. The author failed 

 to find conclusive evidence in the type specimens themselves 

 for the use of the other generic names proposed, namely : 

 Ornithopsis, Seeley, 1870, from the Wealden; Eucamerotus, 

 Hulke, 1872, Wealden ; Ischyrosaurus (preoccupied), Hulke, 

 1871, Kimmeridge; and Cho?idrosteosaurus, Owen, 1876, 

 Wealden. 



jEpyosaurus, G-ervais, 1852 ; Macrurosaurus, Seeley, 1876 ; 

 and Dinodocus, Owen, 1881, all represent forms from the 

 Cretaceous, but their relations to each other cannot yet be 

 determined. 



Discoveries of more perfect specimens may establish the fact 

 that the forms in the different geological horizons are distinct, 

 but as long as the known remains are so isolated and frag- 

 mentary, this point must be left in doubt. 



The European Sauropoda at present known are from deposits 

 more recent than the Lias, and none have been found above 

 the Upper Greensand. In America, this group apparently has 

 representatives in the Trias, was very abundant in the Jurassic, 

 but, so far as now known, did not extend into the Cretaceous. 



Stegosaueia. 



Another group of Dinosaurian reptiles, which the author has 

 called the Stegosauria, from the typical American genus Stego- 

 saurus, is well represented in European deposits. The remains 

 already discovered are more numerous, and in better preserva- 

 tion, than those of the /Sauropoda, and the number of distinct 

 generic forms is much larger. The geological range, also, is 

 greater, the oldest forms known being from the Lias, and the 

 latest, from the Cretaceous. 



These reptiles, although very large, were less gigantic in size 

 than the Sauropoda, and were widely different from them in 

 their most important features. Their nearest allies were the 

 Omithopoda, to which they were closely related. 



