MESODONTA. , 227 



but well developed acute internal cusp. The external cusp is flush with 

 external base of the crown, and is flanked by a small basal lobe both ante- 

 riorly and posteriorly. These lobes are connected with each other by a 

 weak external cingulum, and with the internal cusp by an anterior and a pos- 

 terior cingula of greater strength. No intermediate tubercles. The true 

 molars may be readily distinguished from those of most of the Creodonta, 

 Deltatherium, for instance, by the presence of intermediate tubercles. The 

 external cusps are low and well separated, and are not so far within the 

 base as in Deltatherium and Dklelphys, though they are bounded externally 

 by a low cingulum. The latter terminates in two angles, one anterior and 

 •one posterior, which send inwards cingula, which meet in a prominent 

 angle interior to the middle of the crown. These cingula support also the 

 jntei'mediate tubercles. Another cingulum arises below the intermediate 

 tubercles, and passes round the inner base of the crown, where it has a 

 truncate outline, owing to the development of tubercular angles anteriorly 

 and posteriorly. The differences between the true molars are as follows : 

 The first is smaller than the second and larger than the third. The first 

 and second have a strong tubercle at the posterior inner angle of the cingu- 

 lum; in the third the cingulum only is present. The anterior inner angle 

 ■of the cingulum is much more pronounced in the second than the first 

 molar, and in the third it is not angulate, the inner extremity of the tooth 

 being narrowed oval in outline. In this tooth the posterior external cingular 

 angle is wanting, and the posterior external cusp x-educed in size. 



Measurements. 



M. 



-Length of bases of buperior true molars 0185 



Diameters P-m. iv ^ '^°*''"'P°***«"'"' ^^'^ 



I transverse 0070 



Diameters M. ii ^''"*'^™P°"*'^"'«" 0'^« 



transverse 0085 



anteroposterior 0050 



transverse, at middle 0062 



This species was found by my assistant, Mr. D. Baldwin, in the Lower 

 Hocene, probably Puerco beds of Northwest New Mexico. 



