188 



Bulletin American Museum of Natural History. [\'ol. XX^'II, 



the basal edge of the tooth woukl thus form an imperfect protoloph, across 

 which sheared the incipient protolophid of the lower molar. This proto- 



D. Telmatherium, Middle Eocene Ungulate. 

 Upper molars very wide anteroposteriorly, lower 

 molars long anteroposteriorly. Protocone fitting into 

 basin of talonid, liypocone into basin of trigonid, 

 paraconid vestigial; space between upper molars 

 limited to inner side. 



Pfpa . 



tne 



yAed ilyd 



C. Triisodon, Basal Eocene Carnivore. Upper 

 molars widening anteroposteriorly, metacone equal to 

 jtaracone; lower molars lengthening anteroposteriorly 

 by development of the talonid, which receives the 

 broad protocone. 



■ml pr' 



PS.pOL I , , 



''P^- h%e.4 



B. Dryolestcs, Upper Jurassaic (upper molars 

 after Gidley, lower molars after Osborn). Upper 

 molars wide transversely; lower molars small, short 

 anteroposteriorly, fitting between upper molars. (The 

 latter as drawn may be spread apart too much on the 

 inner side). Talonid incipient, paracone centro- 

 e.xternal, metacone small. 



A. Diademodon, Triassic Cynodont (upper molars 

 after Seeley, lower molars after Broom). Upper molars 

 wide transversely, lower molars small, short antero- 

 posteriorly, fitting between upper molars, prd, 

 protoconid. 



Fig. 12. Projection of upper on lower molars, illustrating the "Wedge Theory. 



lophid was not yet established in Amphitherium but was well developed 

 in Dryolestes, and became very important in many later types. 



The protoloph above was further improved by the posterior limb of the 



