CLASSIFICATION OF THE THEIIIODONTIA. 



81 



is so loaded with a very fine siliceous mud as to be glass-hard, 

 completely blunting a carefully hard-tempered chisel after a 

 single blow. 



The skull is broken through along the plane of the palate, part 

 of that structure adhering to each block. 'I'he skull is then 

 broken through b)^ a split whicli passes through the brain-cavity 

 and removes the whole left posterior corner of the skull behind 

 the orbit. Finally, another split traverses the occiput, part of 

 that region adhering to each surface. 



Where weathering has softened the matrix, very good pre- 

 parations are easily made, and in these regions, especially where 



Text-hijure 23. 



Qu. X" B.5r B.Oc. TB.5p. QU 



8c!/innnsaurHS watsoni Broom. T.ype-skull. 

 Occipital aspect. X -g-. 



the bone has been cleaned by weathering, the preservation is 

 extraordinarily good. Development of the unweathered regions 

 is a verv difficult and extremely slow and tedious process. Never- 

 theless, I have been able to make a satisfactory preparation of the 

 inner surface of the cranial cavity. 



The occiput now shows nearly every detail of its structure, 

 although a direct view of its posterior surface cannot be seen. 

 Its outline is well shown and the posterior surfaces of the quad- 

 rates and squamosals are clean. 



Dr. Broom's figures give a good idea of the general shape, the 

 structure of the dorsal and lateral aspects not being shown. 



Proc. Zool. Soc— 1921, No. VI. 6 



