June, 1912. New Titanotheres — Riggs. 37 



rounded, the post-orbital process elongate. The nasals are convex 

 on the inferior surface owing to the thickening at the sutural line. 

 The molar teeth are long in the crown having inner cones nearly equal 

 in height to the ectoloph. The molar-premolar series is well preserved 

 and unworn in the type specimen. The canines are broken at the 

 alveolus; half of the incisors are preserved. The dentition as a whole 

 is more highly specialized than that of Metarhinus. The first and 

 second incisors have short, rounded, semi-conical crowns indented by 

 cups on the posterior surface. The third incisor has a more elongate 

 crown (23 mm.), the cup is suggested by a prominent cingulum on the 

 posterior margin. An interval of six millimeters separates the third 

 incisor from the canine. The latter is eighteen millimeters in diameter 

 and circular at the alveolar section. The elongate third incisor would 

 indicate a long-crowned canine. The first premolar is a simple, blunt 

 cone with an internal cingulum and emplanted by two roots. Pre- 

 molars 2 , 3 , 4 increase steadily in length of ectoloph and deuterocone; 

 strong internal cingula persist. The last three have taken on the sub- 

 rectangular outline indicating a stage in dental specialization similar 

 to that of Sthenodedes. The molars are long-crowned ; the protocone 

 increases steadily in height from first to third. The hypocone is more 

 prominent in the second and reduced to a vestige in the cingulum of the 

 third. The entire molar-premolar series is more curved than in any 

 other Uintah titanothere. 



In its general proportions the skull of R. abbotti is similar to that 

 of Metarhinus riparius. Somewhat longer and more slender in the 

 arches, the skull suggests a longer-limbed and more active animal. 

 The facial and palatal aspects differ more widely. The anterior narial 

 opening is high and the nasals are not infolded at the base. They 

 terminate above the anterior margins of the canines. There is no 

 antorbital fossa, the muzzle is broad and the canines evidently elongate. 



R. diploconus. 



Type specimen Telmatotherium diploconum Osborn. 



Horizon: Uintah Metarhinus Beds. 



This species should be removed from Metarhinus because of the 

 highly specialized dentition associated with a narrow sagittal crest and 

 the absence of an infra-orbital process. The absence of the nasals from 

 the type specimen leaves its affinities somewhat in doubt. Until these 

 shall be known it is proposed to refer the species to Rhadinorhinus. 

 It differs from R. abbotti in having a more concave profile, somewhat 

 larger molars and a well-developed hypocone on M 3 . 



