328 Principal Forms of the Dinoscmria. 



Palceoscincus, Leidy, 1856, from the Cretaceous, and Pri- 

 conodon of the author, 1888, from the Potomac formation, are, 

 perhaps, allied forms of the /Stegosauria, but, until additional 

 remains are found, their exact affinities cannot be determined. 

 Apparently, the oldest known member of this group in America 

 is the Dystrophins, Cope, 1877, from the Trias of Arizona. 

 In Europe, none have yet been found below the Jurassic. 

 The Euskelesaurus, of Huxley, 1867, from the Trias of South 

 Africa, is apparently a member of this group. 



Okntthopoda. 



The great group which the author has called the Omitho- 

 poda is well represented in Europe by Iguanodon and its 

 allies. The remarkable discoveries in the Wealden of Bel- 

 gium, of a score or more skeletons of Iguanodon, have fur- 

 nished material for an accurate study of the genus which they 

 represent, and, indirectly, of the family. The genus Iguano- 

 don, founded by Mantell in 1821, is now the best known of 

 European forms, and need not here be discussed. Hypsilo- 

 phodon, Huxley, 1870, from the Wealden, is likewise well 

 represented, and its most important characters fully deter- 

 mined. The other genera of this group, among which are 

 Mochlodon, Bunzel, 1871, Vectisaurus, Hulke, 1879, Ortho- 

 merus, Seeley, 1883, and Sphenospondyhcs, Seeley, 1883, are 

 described from less perfect material, and further discoveries 

 must decide their distinctive characters. 



None of these genera are known from America, but allied 

 forms are not wanting. A distinct family, the Hadrosauridce, 

 is especially abundant in the Cretaceous, and another, the 

 Camptosauridte, includes most of the Jurassic species. The 

 latter are the American representatives of the Iguanodontidce. 

 The nearest allied genera are, apparently, Iguanodon and 

 Camptosaurus for the larger forms, and Hypsilophodon and 

 laosaurus for those of small size. A few isolated teeth from 

 each country suggest that more nearly related forms may at 

 any time be brought to light. 



Many generic names have been proposed for members of 

 this group found in America and in Europe, but, in most cases, 

 they are based on fragmentary, detached specimens, which 

 must await future discoveries before they can be assigned to 

 their true place in the order. 



As a whole, the European Ornithopoda now known seem to 

 be less specialized than those of America, but additional dis- 

 coveries may modify this opinion. The geological range of 

 this group, so far as known, is essentially the same on each 

 continent, being confined to the Jurassic and Cretaceous. 



