VERTEBRATE FAUNA OF THE BLANCO BEDS. 59 



to preclude the possibility of the species being identical did no other dif- 

 ferences exist. The differences observed in this tooth may, however, be 

 of specific value. The relative width of the crown is greater, especially 

 anteriorly, and the lateral borders of the latter are not parallel as in T. 

 ahepardii, but converge posteriorly, as in M. proacursor. The lobes of 

 the ci'oss-crests are opposite as in the latter species. From M. prcecursor 

 this tooth differs in the more tubercular and less crest-like character of the 

 cross-crests, and in their more profound division -on the median line, 

 especially in the third and fourth crests. M. prcecursor is zygolophodont 

 while the Mexican species is bunolophodont. The various characters 

 just mentioned also distinguish the M. prcecursor from the T. shepardii. 

 There is no evidence that the Mexican species possesses an enamel band 

 on the superior incisors. My assertion to this effect was based on a speci- 

 men which presents this character which is preserved in the Escuella de 

 Minas of Mexico. This specimen came from Tehuichila, in the State of 

 Vera Cruz, from a formation which I subsequently determined to be of 

 Loup Fork age, so that the identity of the species with that found in the 

 Equus beds of the valley of Mexico is highly improbable. I therefore 

 refer the latter to the genus Mastodon under the specific name of M. 

 oligobunis, Cope. It differs from the Dibelodon tropicus in the smaller 

 number of cross-crests of the last molar, and their greater simplicity, 

 since they are not divided at all, and the external halves of the first and 

 second only have anterior and posterior buttresses, in some individuals 

 at least. 



Measurements of T. shepardii. 



Mm, 



Length of right ramus and symphysis 730 



Length of right ramus to symphysis 515 



Depth of ramus at posterior end of M. iii 135 



Depth of ramus at anterior end of M. ii 175 



Width across both rami at posterior end of M. iii 420 



Width of right ramus at posterior end of M. iii 140 



Width of both rami at base of symphyses 214 



Width of snout at proximal end 65 



Width of distal extremity of symphysis 120 



Length of snout 215 



Diameters of M. ii i anteroposterior 125 



( transverse at middle 75 



Diameters of M. iii i anteroposterior 164 



I 



Diameters of right symphysal tusk ■< 



Diameters of left symphysal alveolus \ 



transverse at middle ,. . . 

 vertical 



. 75 

 68 



transverse 



27 



vertical 



78 



transverse 



. 45 



