34 Annals of the Carnegie Museum. 



blunter, and the lateral ridges are less developed in the present species 

 than in either P. emarginatum or Diplacodon elatum. D. elalum has 

 the canine more nearly of the same pi oportion as in P. emarginatum. 

 The diastema back of the canine is relatively longer and its border 

 much thinner than in P. emarginatum, in which respect it is more 

 nearly like Diplacodon elatum. 



The crown of Pi is so much worn that its characters cannot be made 

 out. It is, however, of greater antero-posterior than transverse 

 diameter, and undoubtedly had a simple structure like that of P. 

 emarginatum. P~ is also much worn especially along the external 

 portion. The external face of the ectoloph is subdivided by a deep 

 vertical groove and is much convex both antero-posteriorly and supero- 

 inferiorly. This deep groove adds greatly to the antero-posterior 

 convexity of the proto- and tritocones. The general outlines of the 

 tooth are less quadrate than in Titanotherium, which is apparently due 

 to the lack of development of the antero-internal angle in the species 

 under consideration. In the type of Diplacodon elatum P- is lost, 

 while the external portion of P- is broken off. In the present species, 

 the deuterocone of P- is less lidge-like than in D. elatum, the two 

 internal tubercles being somewhat better indicated and the lidge 

 between them distinctly less developed. P- is more quadi ate in outline 

 than the preceding tooth, and has two distinct internal tubercles on the 

 crown, which aie separated by a shallow groove, while in Diplacodon 

 elatum these tubercles are united into a solid internal ridge, revealing a 

 distinct dilTerentiation from what is seen in the present species (com- 

 paie Pis. VI, VII, and IX). On the other hand P- both in the type 

 we are describing and in D. elatum, are similar, there being two internal 

 tubercles, deutero- and tetartocones, the former considerably the 

 larger.^ The more important differences in the dentition of the two 

 forms, so far as they can now be compared, seems to be in the pro- 

 portion of the canines, the difference in the length of the premolar 

 series, and the detailed structure of P-. The greater length of the 

 premolar series is naturally to be expected in a form from a lower 

 geological level. 



The detailed characters of the molar series of the geneia heie com- 



8 In No. 2858, the paratype, there is only one internal tubercle, the deuterocone, 

 which may by some be regarded as of sufficient importance to constitute a specific 

 difference. For the present I prefer to regard this character as possiblj^ representing 

 a reversion. 



