part 1] or the upper cretaceous in Hungary. 105 



Thus the primitive KalloJcibotion surviving into the Danian 

 would appear to be a remnant of an otherwise extinct fauna. 



(B) Rhabdodon prtscum Matheron (50). 



[Synonyms : Mochlodon suessi Seeley (73) ; Ornithomerus gracilis Seeley 

 (73) ; and Mochlodon suessi var. robustum Nopcsa (52) ; the last-named and 

 the type of Matheron's genus and species are probably females, while Ornitho- 

 merus is a young specimen.] 



This Orthopodous Dinosaur is closely related to the American 

 Camptosaurus from the Jurassic (32), Kangnasaurus from the 

 Cretaceous (P), 1 and Thescelesaurus from the Lance formation 

 (23). In Europe Camptosaurus occurs in the Kimmeridge Clay 

 (48) and in the Oxford Clay (47). Compared with the European 

 Iguanodon, which evidently once passed through a Camptosaur- 

 like stage of evolution, Rhabdodon seems more primitive, because 

 of the small number of alveoli, and because the mandibular teeth 

 had only one principal ridge and not two. Primitive characters 

 also are the biplane cervical vertebrae, the Hypsilophodon-Wke lack 

 of an expansion on the dorsal ribs (33), the feeble development 

 of the preacetabular part of the ilium, of the pseudopectineal 

 process, and the direction of the fourth trochanter. As in Camp- 

 tosaurus, the ischium is hammer-shaped in the males. It must 

 be mentioned, as a sign of specialization, that the ischium shows 

 no projection forming the inferior border of the foramen obtu- 

 ratorium. 



If we consider that in Belgium, by the time of the Upper 

 Senonian, the Iguanodon of the Wealden had changed to the genus 

 Craspedodon (19), and that the Camptosaurus stage of Iguanodon 

 has to be sought for in earlier beds than the Wealden, the survival 

 of a modified Camptosaurian at the end of Danian times is quite 

 a noteworthy feature. 



(C) Orthomerus transtlvanicus Nopcsa. 



[ Generic, synonyms : Limnosaurus Nopcsa non Marsh (52) ; Hecatosaurus 

 B. Brown (8) ; Tehnatosaurus Nopcsa (55) ; male and female distinguishable 

 by the shape of the base of the centra of the caudal vertebrae, one sex 

 (it is uncertain which) showing a furrow (60, 61).] 



Orthomerus belongs with Kritosaurus (8) to the Protracho- 

 dontidae, or primitive Trachodon group; it is, however, even more 

 primitive than its American relative. Both these Protracho- 

 dontidse differ from the true Trachodontidse, in that the anteorbital 

 part of the skull is not so long as in the latter (9, 10, 32, 39). 



Orthomerus differs from Kritosaurus in the leaf -like asymmetrical 

 shape of the mandibular teeth, which are not compressed antero- 

 posteriorly, but in a linguo-labial direction, and they lack the 

 projecting ridge characteristic of the Trachodontidse. The mandi- 

 bular teeth of Orthomerus approach in these points strongly to 



1 S. H. Haughton, ' On some Dinosaur Remains from Bushmanland ' 

 Trans. Roy. Soc. S. Africa, vol. v (1915-16) p. 259. 



