346 5. W. WILLISTON 



None of the [English] genera are known from America, but allied forms 

 are not wanting. The nearest allied genera are apparently Iguanodon [Wealden] 

 and Camptosaurus, for the large forms, and Hypsilophodon [Wealden] and 



Laosaurus for the smaller forms Moreover we have in America a closely 



allied form [to Hypsilophodon^ Laosaurus, of which several species are known. 1 



And, so far from the American forms being the most generalized, 

 Lydekker says that Hypsilophodon is "the smallest and least spec- 

 ialized member of the family !" Perhaps this opinion is not decisive, 

 but Hypsilophodon certainly cannot be called the most specialized. 

 Lydekker even refers certain Kimmeridge and Wealden species to 

 the American genus Camptosaurus. 



Perhaps the best evidence we have for the Jurassic age of the 

 American deposits is that of Stegosaurus, which is so closely allied 

 to Omosaurus Owen from the Kimmeridge that Marsh believed the 

 two genera to be identical. On the other hand, this type of the 

 predentate dinosaurs seems to range from the Lower Lias in Scelido- 

 saurus, to Paleoscincus from the Laramie, with four or five genera 

 referred to the group from the Wealden. Its value, then, is slight. 



Other evidence offered by the reptiles from the American beds 

 is slight. A genus of crocodiles called by Marsh Diplosaurus seems 

 to include Hyposaurus vebbii Cope from the Comanche Cretaceous 

 of Kansas. Years ago Zittel referred both of these forms to the genus 

 Goniophilis from evidence communicated by Professor Marsh, 

 and Goniophilis is said to be "a genus very characteristic of the 

 Wealden" (Lydekker). The recently published figure of the type 

 specimen of Diplosaurus, when compared with figures of Goniophilis, 

 shows a startling resemblance. Indeed, so far as I can learn, there 

 are no brevirostral crocodiles known from below the Purbeck or 

 lithographic slates. The evidence, then, of the crocodiles is decidedly 

 for the uppermost Jurassic or Wealden age of the American beds. 



Of the Chelonia the single species Compsemys plicatulus Cope 

 {Glutops ornatus Marsh) is not at all decisive. If the species is 

 correctly referred to Compsemys, all its related forms are of Cretaceous 

 age. Nor is there any evidence to be obtained from the pterosaurs 

 or birds. Of the mammals I will not venture to speak, save that I 

 think that there are too few forms known from the Wealden to offer 



1 American Journal of Science, November, 1895, p. 411. 



