1869.) DR. J. E. GRAY ON THE TORTOISES. 199 
central concavity behind it. Lower jaw very strong, short, with a 
narrow erect front edge ending in a central conical prominence ; 
broad and flattened out behind, especially just before the condyle. 
The tympanic concavity opens into the larger cavity that occupies 
the whole of the mastoid bone. 
Gis" is 
Tetraonyx haska. Two-thirds of nat. size. 
