106 BARON F. NOPCSA ON THE PRIMITIVE REPTILIA [vol. lxxix, 



the hypothetical shape of teeth which must have given rise to the 

 highly ornamented teeth of the Kaloclontidse on one side, and to 

 the teeth of the true Trachodontidse on the other. To a certain 

 extent, thej r resemble the teeth of the Ceratopsian genus Brachy- 

 ceratops (24). The number of teeth is in Orthomerus smaller 

 than in Kritosaurus. Although not great in number, these three 

 features are quite sufficient to fix the primitive nature of Ortlio- 

 merus, the skeleton of which has not yet been thoroughly studied. 

 Since the Trachodontidse occur throughout the whole of the 

 North American Upper Cretaceous, and since they must have been 

 derived from an Ort honierus-Yike type, the occurrence of a Pro- 

 trachodon at the end of the Cretaceous Period in Europe is 

 again an atavistic trait. 



(D) Stritthiosaurus transylyanicus Nopcsa (59). 



[Generic synonyms : Cratmomus Seeley (73) ; Pleuropeltus Seeley (73) ; 

 Rhadinosaurus Seeley partim (73) ; Danubiosaurus Bunzel (13) ; Leipsano- 

 saurus Nopcsa ? (63) ; of the species StrutMosaurus lepidophorii.s the female 

 has been described as 8. paivlowitchi (58) ; the sex of 8. transylvaniciis has 

 not yet been determined.] 



So far as can be seen at present, StrutMosaurus is a relative of 

 Stegoceras of the Belly River formation (40), of Nodosaurus of 

 the Benton (44), and of Polacanthus (56) of the Wealden. 

 Another relative of StrutMosaurus is the imperfectly-known 

 Acanthopholis of the Cambridge Greensand (71). On comparing 

 StrutMosaurus with Stegoceras, it can be seen that in the latter 

 the backward direction of the condyles is more marked, the 

 skull- bones are thicker, the pittings on the surface are more 

 distinct than in StrutMosaurus, and the upper surface of the 

 skull projects farther backward ; but otherwise the two genera 

 seem to agree very closely. The dorsal vertebrae of StrutMosaurus 

 approximate to those of Polacanthus (56) ; the anterior dorsal 

 ribs show the same symmetrical T-shaped section as in all 

 Thyreophora, 1 and differ in shape and function from the asym- 

 metrically T-shaped and bird-like anterior dorsal ribs of the higher 

 Orthopodous Dinosaurs ; the posterior dorsal ribs of Struthio- 

 saurus show a tortoise-like lateral expansion, but are not blended 

 together as in Polacanthus. The segmented armour of Nodo- 

 saurus (44) suggests the probability that here a similar structure 

 may be expected in the lumbar region. The femur of Struthio- 

 saurus agrees with the femur of Polacanthus (56) and Nodosaurus 

 (44), but better still with the European Gryptosaurus from the 

 Oxford Clay (47). The dermal armour is thinner than in Pola- 

 canthus or Hierosaurus. Summarizing all the characters that we 

 have been considering, it is well nigh certain that StrutMosaurus 

 is a type from which (to some extent) Polacanthus could be 

 derived, but not vice versa. The bird-like shape of the basis cranii 



1 This term (58) was proposed in 1915 to comprise all the armoured 

 Dinosaurs: namely, Stegosauridse, Acanthopholidse, and Ceratopsidas. 



