60 MAMMALIAN DENTITION 



a type molars of Dryolestes are figured (Fig. 16). The upper 

 molars are dissimilar in form from the lower molars and in this 

 the Trituberculates differ from the Triconodonts. The upper 

 molars again are very wide transversely and larger than the 

 lower molars. The protocone on the inner side of the crown 

 fits like a pestle into the mortar-shaped talonid of the corre- 

 sponding lower tooth. Paracone and metacone are present and 

 between the latter and the protocone a smaller cusp, the meta- 



Fig. 16. — Molar teeth of Dryolestes sp. Jurassic, America. (After Gidley.) Upper 

 figure. Deft upper molars (left) and first right upper molar (right). Dower figure. 

 Left upper molar, lateral (right) and posterior (left) views. Dryolestes represents 

 a stage in which the upper molars, though more numerous (8) than in higher Mammals, 

 were narrower antero-posteriorly. 



comde. On the buccal side of the para- and metacones are two 

 outlying cusps, the parastyle and metastyle. 



In later Mammals we shall see that as the talonid grew 

 larger and more prominent the protocone became depressed. 

 A further cusp, the hypocone, began to appear from a spur-like 

 internal cingulum and fitted into the trigonid of the lower 

 molar next behind. The hypocone is the cusp of the talon or 



