Douglass : Vertf.rrates from Montana Tertiary. 189 



Depth of mandible at prismatic premolar 13 



Depth of mandible from top of condyle to bottom of angle 30 



Height of premolar 14 



Length of premolar at alveolar border 6 



Length of M ^ 4 



Width of uj 3 



Length of M^ 3 



Width of M^ 2.5 



Found in bhiffs of Lower Madison valley, Montana. 



Mylagaulus proximus sp. nov. 

 No. 842. Fig. 27. 



Part of a mandible with the anterior portion and the angle gone. 

 It is smaller and less robust than the corresponding part of Af. prox- 

 imus, not being so deep, so thick, or so long. The condyloid proc- 

 ess is shorter and not so broad antero-posteriorly, and the articular 

 process is broader transversely. 

 This is a somewhat younger ani- 

 mal than the preceding. 



When the animal died the large p\ x 



permanent premolar was erupting *^^>-!^'5-^^i^''^-^^'^ 



and had nearly reached the alveolar 

 border. This tooth, being much 

 larger than its two predecessors, the 



portion of the jaw containing the ""^^^^^ - S-^ i« f.'s?/ 



roots of the latter had to be ab- ^^ 



sorbed. A small part of this alve- Pm^Ms^^- 



olar portion, with one root of the '^ 



anterior temporary molar remains V*^i«^^^^^S: er.-^ '' 



above the postero-e.xternal portion „ ., , , ^ . ,,, 



' ' riG. 27. JMylagauhcs proximtis \^o. 



of the large premolar. The last 3^3 ^ Lower Madison valley. |nat- 



temporary molar being unreduced ural size. «■, inner vievir of portion of 



in antero-posterior diameter was mandible. The large permanent pre- 



being pushed out by this new tooth. "^^l^-" <-'>-uption. b, the same, upper 



,„, . , , , view ; p, permanent premolar ; <ip,^, 



Ihis last temporary molar has a , , 



'^ -' "P\i temporary molars. 



larger grinding surface than that of 



M. proximus, but is low, nearly worn out, and has two long slender roots. 



P 4 is not as large, but it would undoubtedly have become larger 



as there is a considerable space between its posterior border and the 



anterior border of M ;,. This last tooth is long vertically on account 



