Marsh Collection, Peabody Mnseuin. 35Y 



a-conchision wliich has been already reached by Osborn. The 

 more important features of the upper teeth of this species may 

 be stated as follows : There are three molars, of which the first 

 and second are subequal, with the third smaller; the crown has 

 three main cusps and a faint indication of the fourth ; the two 

 outer cusps are more or less crescentic in structure ; there is a 

 small though well-marked mesostyle ; both intermediates are 

 present in the first and second molars, but the posterior is 

 absent in the last; the fourth premolar is molariform, but 

 lacks any trace of the posterior intermediate. I give here- 

 with a reconstruction in outline of the dentition, figure 112, as 

 derived from several specimens. 



112 



111 



Figure 111. — Upper molar of Microsyops elegans Marsli (type of 'Palceac- 

 odon verus Leidy) ; crown view ; twice natural size. (After Leidy.) 



Figure 112. — Upper and lower jaws of Microsyops elegans Marsli ; side 

 view ; natural size ; composed from several individuals. 



The measurements of the type of Microsyojps elegans are as 

 follows : 



From base of posterior root of last molar to anterior ex- 



treraitj^ of crown of fourth premolar le'D™"" 



From base of posterior root of last molar to anterior 



extremity of crown of first molar l 1 1 •() 



Length of fourth premolar and first and second molars 11*0 



Length of first and second molars V'S 



The measurements of the type of Mesacodon speciosiis are : 



Length from posterior root of last molar to base of inci- 

 sor 20-0"^"^ 



From base of incisor to posterior extremity of fourth 



premolar ._ Y'o 



Depth of jaw at posterior border of symphysis 8*0 



Depth of jaw at last molar ._ 7*0 



Measurements of the last lower molar and upper teeth of 

 other specimens : 



Length of upper molars ._ _ lO'S"^"" 



Length of upper molars and fourth premolar. _ ] 4*5 



Length of last lower molar ._ 5*0 



Length of second and third lower molars 8*5 



