lib' University of California Publications in Geology [Vol.9 



A very interesting specimen, belonging to the Museum of History, 

 Science and Art of Los Angeles, is a portion of the left maxillary 

 bone with the three milk molars in postion (fig. 2). Dm- is consider- 

 ably worn, and no lakes are present. Dm 3 is also much worn, but there 

 is still present a fairly large posterior lake and a small anterior one 

 which is almost lost. Dm 4 is almost identical with permanent M 1 

 in form. The total length of the row of milk teeth is 21 mm. while 

 the premolar series in Antilocapra measures 28 mm. The length of 

 Dm 4 is 9 mm., while that of the permanent M 1 is 10 m. 



Since 1911, when Taylor's description was written, enough lower 

 jaw material has been accumulated to give an acquaintance with 

 practically all the teeth of the lower jaw of both milk and permanent 

 dentition, as well as with the general proportions of the jaw itself. In 

 general it may be said that the dentition, in both sets, strikingly 

 resembles that of the modern pronghorn, although there are a few 

 significant differences. 



Dm 2 , the first cheek-tooth of the lower jaw, is a narrower tooth 

 than the permanent P L , of Antilocapra, and not as well developed, 

 and has a much shallower anterior open valley, though in general they 

 resemble each other. 



Dm,, and permanent P 3 resemble each other in that the anterior 

 valley is open on the inner side in both, but they differ in size, the 

 permanent tooth being shorter than the milk tooth, but broader and 

 heavier. P 3 of Capromeryx is very much simpler than the same tooth 

 in Antilocapra, the lobe posterior to the open inner valley being 

 unmodified in the former, but furnished with an enclosed lake in the 

 latter. 



Dm 4 is a three-lobed tooth, very similar to Dm 4 of Antilocapra, 

 but relatively a little larger. Permanent P 4 however, which replaces 

 it, differs very considerably, not only from its own predecessor, but 

 from its counterpart in Antilocapra as well. To a striking extent, 

 it resembles permanent P 3 of Antilocapra, having the anterior valley 

 wide open on the inner side, and a well-marked outer posterior groove 

 as well as one on the posterior margin of the tooth. The last is not 

 deep, and is therefore noticeable only on very slightly worn teeth. 



Permanent M 1 and M, are so similar to those of Antilocapra that 

 no points of difference in them can be picked out, so far as form is 

 concerned. M 3 , however, is more primitive than M 3 of Antilocapra 

 in the inferior development of the fourth lobe or heel. While in the 

 modern species this tooth normally has a very distinct fourth lobe. 



