THE TRIAS OP GEAAFP REINET, S. AFRICA. 415 



in. lin. 



Length of centrum , 1 6 



Height of centrum 1 9 



Depth of articular terminal concavity (hinder) .... 9 



Height of neurapophysis including postzygapophysis 1 6 



Height of neural spino 2 



Length of base of spine 9 



Length of summit of spine 1 



Thickness of summit of spine 4 



Breadth of rib 6 



Thickness of rib 4 to 3 



Length of best-preserved rib 7 



Of the genera of S.-African Triassic Eeptilia hitherto indicated by 

 vertebrae (not differentia-ted like those of the " tretospondylian " 

 group), the following differences are shown in comparison with the 

 present genus. 



The dorsal vertebrae of Platypodosaurus are smaller than the 

 caudal ones of Massospondylns * the centrum of which is 4 inches 

 3 lines in length. Of Pachijspondylus* the caudal centrum is 2 

 inches 6 lines in length; that of Lej)tosp)ondylus* is 2 inches 2 

 lines in length. Tlie formal differences of these caudals suggest 

 more marked ones in the thoracic vertebrae of the same genera ; but. 

 none have as yet been received. 



The vertebrae of Platypodosaurus agree more closely with those of 

 the Anomodont Eeptilia {Dkynodon and Oudenodon) f ; they differ 

 in the minor depth of the terminal concavities from the vertebrae of 

 KisticepTialus i and AntJiodon§. 



The nearest ai)proach to the biconcave structure of vertebrae in 

 existing Mammals is shown in a Monotreme (Echidna) in which the 

 unossified part of the ends of the centrum is dense at its periphery, 

 and presents a definite cavity («) filled with fluid || (PL XVI. fig. 4). 



Sternum. — Save in the instance of Kisticephalus microrhinus and 

 Saurosternon Bainii, I have sought in vain for evidences of sternal 

 structure in the S.-African reptiles until the exposition of the fossils 

 here described. 



The flat symmetrical bone (PI. XVI. fig. 5), hexagonal, but with 

 the angles so rounded off as to approach a circular form, I regard as 

 the anterior one of the sternum proper, repeating in its large re- 

 lative size that which is usually unossified in modern Lizards, but 

 which is well ossified in Ornitliorhynclius (ib. fig. 6, a-c). 



'■'■ The vertebrae referred to the above genera are described in my ' Catalogue 

 of the Fossil Eeptilia and Pisces in the Museum of the Eoyal College of Surgeons 

 of England,' 4to, 1854, pp. 97-100. They were transmitted by Ch. E. H. Orpen, 

 Esq., M.D., from the Drakensberg range of mountains, near Harrismith, Cape 

 of Good Hope, and from a formation which, by indications afforded by the 

 donor's letter, I sta,ted to be " probably of the age of the New Eed Sandstone in 

 Europe," 



t Cat. S. Afr. EeptiHa, 4to, 1876, pp. 40, 43, pis. xxxv., lii., Hii. 



X Op, cit. p. 63, pi Ixix., § Ih. p. 88, pi. Ixx. fig. 2, 



II Art. Monotremata, Cyclop, of Anat. vol. iii. 1841. 



