356 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



external and internal cingula are extremely progres- 

 sive, the external cingula being well defined across the 

 base of the protocones and tritocones, and the inter- 

 nal cingulum forming a wide basal shelf extending 

 around the whole anterior as well as the posterior in- 

 ternal border of the crown. P^ is thus almost like p' 

 (except for its smaller size and relatively smaller 



by the more advanced condition of the deuterocone 

 of p", of the tritocones of p^"*, and of the internal 

 cingula. At the same time the premolars of S. in- 

 cisivus simulate those of Dolichorhinus longiceps, espe- 

 cially in their advanced tritocones, but are distin- 

 guished from them by their greater breadth and far 

 heavier internal cingula. A still nearer resemblance 



Figure 301. — Type skull of Sthenodectes incisivus 



Ona-fourth natural size. Carnegie Mus. 2398 (type). About 3 miles northeast of well 2, Uinta Basin, Utah; upper levels of EobasUevs-DolichorMnus 



zone (Uinta B 2). Ai, side view; Ai, top view; A3, palatal view. 



transverse diameter), whereas in the type of T. ulti- 

 mum p^ is much simpler than p^ P'* (ap. 23 mm., tr. 

 32) and p* (ap. 23 mm., tr. 39) are correspondingly 

 advanced but unlike T. ultimum show no trace of 

 tetartocone ridges and swellings. 



The premolar series is thus readily distinguished 

 from that of the contemporary Manteoceras uintensis 



is with the premolars of Metarhinus earlei, in which 

 p^ is almost as progressive and p^ and p* have heavy 

 internal cingula. 



Molars. — The molars of the type are distinguished 

 from those of T. ultimum by the greater minimum 

 transverse diameter of m\ m^, by the less prominent 

 hypocone on m", by the weaker internal cingula on 



