742 



THE AMERICAN NATURALIST [Vol. XLI 



The close similarity of the lower molar-premolar series of Chali- 

 cotherioidea to that of Titanotherium and Palaeosyops is well 

 known. As in the European forms, the present genus has also 

 the premolars reduced to three teeth in both upper and lower jaws, 

 while in the Titanotheridae there are four. in Moropus is quite 

 simple in structure, while P3 is more nearly like 1\ in Titanothe- 

 rium. The internal tubercle of P4 in jMoropus is somewhat heavier 

 than that in Titanotherium, otherwise the tooth suggests that of 

 the latter genus. Mj and M2 in Moropus are similar to those in 

 Titanotherium. ^Nlg in the latter genus has a prominent posterior 

 heel which is lacking in IMoropus. This thirrl lobe of is also 

 lacking in the Wasatch genus ^Meniscotherii'm. 



The deciduous upper molars (No. 1700) in ^Moropus are more 

 nearly molariforni tlian are the permanent premolar series.^ 

 Deciduous ^l* (d* and dm* in Figs. 24 and 25 respectively) may 

 very easily be taken for the permanent ISP, if extreme care is not 

 exercised in the study of the dentition. The permanent P* cuts 

 the alveolar border shortly after permanent W is entirely erupted. 



Diameter of skull, from cxicnial andiToi v meatus to extreme 



anterior point of maxillary. 305 



Diameter of skull, from external auditory meatus to anterior 



l)order of the orbit, * 160 



Diameter of skull, from anterior border of the orbit to extreme 



anterior point of the maxillary, 150 



Transverse diameter of the frontals over the orbits, 160 



