Farr.] ^*^ [May 15, 



former we can trace a tendency toward the establishment of the 31. in- 

 termediiis type. 



The skull of Jif. intermedins is much more equine in character than 

 that of if. hairdi. It presents the following differences which may be 

 looked upon as modernizations : (1) Increase in length, size and in gen- 

 eral proportions. The largest skull of if. 6cnV(Zi observed measures 218 

 mm., while that of M. intermedins measures 280 mm. (2) The upper 

 incisors are all pitted (see Fig. 0), while in the smaller species only the 

 p. J. two outer pairs have the enamel invagination. 



(3) The facial region of the skull is more elon- 

 gate and the orbit is shifted backward. In M. 

 hnirdi the anterior border of orbit is over M. 1 ; 

 in M. intermedins it is over interA-al between 

 Ms. 2 and 3. (4) The diastema between Pm. 1 

 and the canine is proportionately greater in the 

 larger species. 



/% 1^ "^^^^ canine has a well-developed cingulum on 



\^ ^ its internal surface. This is the foreshadowing 



„ ^ of the cupping, as the pit in an incisor tooth is 



Superior Incisors and i i »> i 



Canine OF M. inter- formed by the cingulum, which rises up on the 



MEDius, J. internal border of the tooth to enclose the de- 



pression. Teeth have been observed from the lower Oreodon beds which 

 have a strongly developed cingulum anticipating the development of the 

 pit. (5) The occiput is slightly more overhanging in the larger species. 

 (6) The aveolar border of the jaw is better developed and higher in M. in- 

 termedins. This, of course, is correlated with larger teeth, with longer 

 roots. (7) The postorbital processes are better developed, more nearly 

 enclosing the orbit. (8) There is in 31. intermedins a large deep ant- 

 orbital fossa or depression occupj'ing nearly all of the lateral wall of 

 skull and extending forward almost to Pm. 1. (9) Tlie teeth of the 

 molar series are much larger, longer and more specialized than those of i/. 

 bairdi. These diflFerences, which have been given by Osborn and Wort- 

 man in their description, are: {a) "The internal cingulum of Pm. 1 is 

 more strongly developed and a distinct basin is formed. (6) In the sec- 

 ond upper premolar, the parastyle or antero-exterual buttress is consider- 

 ably larger than in 3f. bairdi and gives to the crown an incipient trian- 

 gular shape. (<■) The midrib of the external lobes is better developed 

 than in 31. bnirdi, and the postero-transverse crest is more nearly con- 

 fluenced with outer wall of tooth." 



Length of 3folar-P)-emolar Series. 

 31. bairdi ... . 73.5 31. intermedins.... 97 3f. prastans.... 112.5 



Molar Series. 

 23 46 51 



Pi'emolar Series. 

 42 53 61 



