46 



ROYAL SOCIETY OF CANADA 



No additional teeth from the lower jaw were obtained last summer. 

 Figures of the two lower molars are given in Cope's memoir of 1891. 



Measurements of upper molar of M. westoni, 

 obtained in 1904. 



Transverse diameter 013 



Anteroposterior diameter 0102 



Height of protocone 0045 



Height of hypocone 0045 



Height of ectoloph 0062 



Measurements 



of tj'pe molar of 



M. westoni as 



given by Osborn. 



Measurements 



of Ml (type) of 



M. m jntanensis 



as given by 



Osborn. 



.014 

 .0105 



Mr. Gidley is of the opinion that the tooth collected last year 

 approaches more closely to M. montanensis than to il/, westoni, and is 

 inclined to refer it to the former species with some degree of doubt. 

 In comparing it with M. montanensis he notes the somewhat less elevated 

 inner cones and the presence of an internal cingulum, which he regards 

 as differences of perhaps not more than varietal value which may be 

 explained by calling the tooth a premolar instead of a molar. 



Judging from the characters of the teeth and their size it is evident 

 that the two species M. westoni and M. montanensis approach each 

 other closely. The type of M. westoni is not as well preserved (nor as 

 accurately figured in the original description) as is desirable, and the 

 absence of the ectoloph and the anterior margin, including the front 

 slope of the protoloph, precludes the taking of exact measurements. 

 That the tooth of last summer's collecting (figures 1, la-c) comes from 

 the same locality as the type of M. westoni, and that it has a particu- 

 larly well defined internal cingulum are facts worthy of every consider- 

 ation in determining its specific afi&nity. 



Mesohippus pr^cocidens, sp. nov. 



Plate IT, fig. 2. 



Left upper molar {imperfect). 

 Measurement : 



Eeiglit of protocone 0047 



It is with some hesitation that the writer designates this tooth by 

 a new specific name which may be considered entirely provisional until 

 more perfect material is available. The tooth lacks the ectoloph and the 

 ])ostcrior border with the hinder slope of the hypocone, but is otherwise 



