No. 492] SOME AMERICAN CHALICOTHERES 741 



The molar-premolar series of jNIoropiis has a general similarity 

 to that of the Titanotheres, but a brief comparison of the more 

 important differences is thought to be of interest in this connection. 

 The external walls of the upper premolars of Titanotherium are 

 excavated, forming a transverse median valley on the grinding 

 face of the teeth, while in IMoropus the walls are highest in the 

 middle, and this portion of the tooth is not divided by a trans- 

 verse valley. The internal cusps of all the upper premolars in 

 Titanotherium have a tendency to become divided so as to form a 

 larger anterior and a smaller posterior tubercle. In Moropus the 

 single tubercle is crescentic, especially on V\ On the molars of 

 Titanotherium there are two distinct internal tubercles, while in 



Moropus there is only one tubercle and a transverse cutting lobe 

 on the posterior internal angle of the tooth. This transverse lobe 

 which unites with the external part of the tooth has apparently 

 taken the place of the posterior internal tubercle (hypocone) of 

 Titanotherium and is similar to that of ^leniscotherium as was 

 pointed out by Professor Osborn in comparing the latter with the 

 known genera of the Chalicotherioidea/ The n])])er molars in 

 Moropus are relatively longer and narrower than in the Titano- 



of the best known forms of ( 'halic<)theri..iJra in Knr..],!- and Asia.^ 



'On Plate IH.. figs. 3, 4. aiid o in Depeivfs Memoir. I. r.. are figures of 

 upper molars which more nearly agree in diameter \\ith those of Moropus. 



