1897.] Trituberculy : 1003 
cusps the equipment of the lower molar.was complete, and it 
was ready for transformation into the molar of a i un- 
gulate or carnivore, as the case might be. 
But why notice such a detail as the posterior intermodikta 
cusp or hypoconulid? Because, to give only two reasons, this 
1 0 0 0 2 eee 
a a l NA 
VAWA © VEAP Ol 
o VARIAN » UF 
Fig. 7.—PHYLETIC AND ‘MECHANICAL HISTORY OF THE (See CuspPs, 
A. Reptilian stage, Haplodont, Permian. B. Protodont stage (Dromatherium) 
Triassic. C. Triconodont stage aA D. Tritubercular stage ( Spala- 
cotherium). E. Tritubercular-tuberculo sectorial, Lower Jurassic. F. The 
same, in Upper Jurassic. G. The same, in Upper r Cretaceous. H. The same, 
Puerco, Lower Eocene: J. Sexitubercular-sexitubercular, Puerco. J. Sexi- 
tubercular-quadritubercular, Wahsatch, 
cusp plays an important rôle in the ungulates ; itis invariably 
present, except perhaps in the Coryphodons, and forms the 
third lobe of the last lower molar, which is thus proved to be 
