112 



Baron F. Nopcsa — British Dinosaurs- 



to the type of St. imgulatus and 0. armatus. Several differences, 

 however, may be noted as distinguishing this species quite clearly 

 from either of the others. 



In St. %mgulatus the point from which the diapophysis arises is much 

 higher above the bottom of the neural canal than in our specimen ; 

 in 0. armatus this point is very much lower. Corresponding with 

 this difference the elevation of the prezygapophysis in our specimen 

 is also intermediate between that in the two other animals ; while 

 0. Lennieri shows much the same stage of specialization as 0. armatus. 

 The direction of the diapophyses is also different in the different 

 animals, for they are directed more outward than upward in 0. armatus, 

 more upward than outward in St. imgulatus, and equally outward 



FIG. 2. Diagram illustrating the difference of strain on the diapophysis as 



correlated with the elevation of latter, a. Stegosauriantype. b. Omosaurian 



type, p = parapophysis ; d = diapophysis ; x = weight of dermal armour 



acting on the rib by m ; y = amount of vertical pressure ; a (a!) = pressure 



on parapophysis ; /3 (/3'j = strain on diapophysis. 



and upward in St. prisons, the angle that they form with the neural 



spine being in the latter just about 45 degrees. Comparing these 



data with Scelidosaurus, we remark that the elevation of the 



diapophyses steadily increases as these animals specialize. Since the 



bones of these animals are not pneumatic, and since a similar elevation 



is not present in the mammalia, though in these the development of 



lungs is much more important than in reptiles, I do not believe this 



elevation had anything to do with the development of the lungs^ as 



generally accepted, but I think it is rather due to the increasing 



