PETERSON: THE AMERICAN DICERATHERES. 419 



P* is very much worn, so that its configuration is practically obliterated. 

 P- is also much worn, but plainly indicates that the cross-crests are more swollen 

 than in the larger species, D. armatum, so that on extreme wear of the tooth the 

 two crests become almost united internally and more nearly approximate the 

 condition in the Nebraskan form D. cooki; there is a slight indication of a crochet 

 in P'. P^ has the internal portion of the cross-crests even more closely united, 

 so that on extreme wear the tooth has a remarkably close similarity to that in 

 D. cooki. There is, however, no crochet shown in this worn tooth; the crista might 

 be said to be represented by a heavy fold on the inner face of the ectoloph. P* in 

 its general characters is practically a repetition of P'*, except that the crista and 

 crochet are more plainly shown. The crochet of P* of this species represents, 

 undoubtedly, the most external process of the comb-like plate on the posterior 

 border of the medifossette in D. cooki; that is to say, the true crochet, which unites 

 with the ectoloph on extreme wear of the tooth. In the forms of the John Day it 

 appears that this crochet does not entirely unite with the ectoloph. 



No. 10,004 of the Yale Museum Collection (Marsh's type of D. nanum) 

 is laterally compressed by crushing. As a consequence the nasals appear less 

 broad than otherwise would be the case, and they are also possibly somewhat 

 lengthened by crushing. The horn-cores are well-developed and the points of 

 the nasals are quite heavy, and extend well in front; their tips are broken off. 

 The nasals as a whole are heavy and are elevated above the premaxillaries much as 

 in later forms, thus presenting large anterior nares. The infra-orbital foramen is 

 large, well up upon the maxillarj' and its posterior margin is opposite the middle 

 of P^ The premaxillary is long; it is also slender, though somewhat heavier than 

 in the later forms from Nebraska. There is a large upper incisor of the usual 

 cutting pattern. The premolars are very much worn. 



The lower jaws of the same specimen are also slightly crushed laterally. 

 The most noteworthy feature of these jaws are the proportionally large median 

 incisors and the long diastemata from the cheek-teeth to the incisors. The lateral 

 incisor is robust, well sharpened by wear and procumbent in position. The cheek- 

 teeth are much worn, indicating the senility of the individual. There is a fairly 

 well developed cingulum on the lower premolars (PI. LVIII, Figs. 1-3.) 



As in the lower jaw of D. armatum, the ramus is quite heavy, but somewhat 

 deeper in proportion. The internal face is also less convex supero-inferiorly. 

 This latter character may in part be due to crushing. 



As stated above, the skull (No. 7324 Cope Collection) in the American Museum 

 is by far the best of the three specimens here described. (See Pis. LXIII Fig. 6; 



