JL54 ANNALS NEW YORK ACADEMY OF SCIENCES 



Eemains of the Saiiropoda are spoken of as 'frequent' in the Wealden, 

 while from the Middle Jura only a few are known, and all these are of 

 one, or at most two, species. I certain!}' cannot see what evidence these 

 forms present that would lead one to say that the American forms are 

 clearly Jurassic. The range of this suborder, so far as is known, is from 

 the Middle Jurassic to the Upper Cretaceous, though there may be doubt 

 as to the real age of the Indian form. Their known geographic distribu- 

 tion is Europe, India, Madagascar, Africa, South and Korth America — 

 that is, over the whole world. The generalized characters presented by 

 them are not at all sufficiently well understood to say off-ha-nd that certain 

 forms are older than others. . . . 



■^'It is quite true that the Brachiosauridas of Riggs (Brachiosaiirns 

 Riggs and Haplocanthosaurus Hatcher) have a more generalized structure 

 in this respect than has Cetiosaurus even, but we have no reason to 

 assume that all the generalized forms died out with the advent of special- 

 ized ones, such as are most of the American Sauropoda. JSTor do I think 

 it quite certain that the Brachiosaurida? are the most generalized, cer- 

 tainly not if the hypothesis that the Sauropoda have been derived from 

 primitive ornithopoda is at all probable. Furthermore, the genus PJeuro- 

 ccelus, originally described from the Potomac beds, has been recognized in 

 the Atlantosaurus beds by Marsh, and later by Hatcher, and forms from 

 the Wealden have been referred, provisionally at least, to the same genus. 



"For the most part, the carnivorous dinosaurs have little value in the 

 correlation of the horizons. Megalosaiinis is reported from Europe from 

 the Lias to the Wealden. In America we have three or four genera of 

 the Megalosauridse in the Atlantosaurus beds, Creosaurus, AllosoAirus, 

 Antroclesmus, and Ceratosaurus, and the family survived to the Laramie 

 Cretaceous. CceJunis was described from the Atlantosaurus beds, but is 

 known to occur in the Potomac beds. In the Wealden of England 

 Aristosuchus is very closely allied, indeed is supposed to be identical, and 

 all the other genera referred to the Cceluridse are from the Wealden. 

 In the extensive hollowness of the bones of the skeleton, CceJurus is not 

 only the most specialized of dinosaurs, but of all vertebrate animals. 

 The evidence then to be derived from the Theropoda is for the con- 

 temporaneity of the Wealden with the Atlantosaurus beds. 



"So far from the evidence of the Iguanodontia being against this 

 correlation, I believe that it is decidedly for the identity of the two 

 horizons. Iguanodonts are found in abundance in the Atlantosaurus 

 beds, and of the largest size and high specialization. . . . And, so 

 far from the American forms being the most generalized, Lydekker says 

 that HypsilopJiodon is 'the smallest and least specialized member of the 



