51 



-K- c c , I antero-posterior 48 



Diameter or first molar < , r 



( transverse 29 



tv , . e 1 , I antero-posterior 58 



Diameter of second molar < . r 



| transverse 33 



rv . n , , ■ , , I antero-posterior 82 



Diameter ot third molar < . r 



t { transverse , 33 



Megacerops assiniboiensis. ISTom. prov. 



Plate V, fig. 6, and plate VI, fig. 3. 



A robust, short, left mandibular ramus, belonging to the 1904 collection, indicates a 

 species distinct from M. angustigenis and M. primitivus. In this specimen the three molars 

 and the fourth premolar are preserved, with the roots of the third premolar. The posterior 

 end of the ramus is missing, as well as the anterior end in advance of the third premolar. A 

 part of the right ramus next to the symphysis remains. 



The jaw is much deeper, thicker and relatively shorter than in angustigenis and primitivus, 

 and the teeth are much larger than in these species. It is narrow anteriorly, and the symphysis 

 extends back to a point in line with the division between the fourth premolar and the first 

 molar. The bone is massive and heavy throughout. The mental foramen is placed beneath 

 the posterior root of the third premolar, farther back than in M . primitivus. 



The cingula are very slightly developed. The external cingulum is present for a short 

 distance only, on the anterior face of each of the four teeth, and in the third molar in 

 advance of the heel. The only trace of an internal cingulum is to be seen in the third molar 

 on the posterior slope of the heel. 



The fourth premolar is fully molariform. The teeth are stout, and of about the size of 

 the corresponding ones in M. marshi, Osborn, but the jaw is relatively shorter than in this 

 species. 



From the material available, the species, for which the provisional name assiniboiensis is 

 proposed, cannot be definitely characterized. 



Measurements of ramus. Type. 



MM. 



Depth of ramus at posterior end of fourth premolar , 80 



" " " third molar 156 



Thickness of ramus above lower border beneath posterior end of first molar .... 55 



Vertical thickness of symphysis a little in advance of its posterior termination. . 53 



Vertical thickness of symphysis in line with front root of third premolar 31 



Space occupied by fourth premolar and the molars 260 



tv £ » ,, ,| antero-posterior . 41 



Diameter ot fourth premolar ', , r ., , 



1 | transverse , 6 1 



Dc a ^ i antero-posterior 55 



lameter of first molar -! , r oa 



I transverse oo 



r.- » i , I antero-posterior. . . , 71 



Diameter ot second molar. . . r , , 



I transverse 41 



-p.. c j.i_ • j i I antero-posterior , 99 



Diameter ot third molar... . < , r , „ 



I transverse , 4o 



Space occupied by roots of third premolar (antero-posterior) 34 



Space between fourth premolars (twice the distance of fourth premolar from 



vertical plane through symphysis) , 60 



