66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



Discussion. — Diplobunops vanhouteni would appear to fulfill in all 

 respects the requirements for a stage ancestral to the upper Uintan 

 species of Diplobunops. Moreover, it more closely resembles con- 

 temporary forms of Protoreodon than do the later representatives of 

 Diplobunops. The skull is nearly the size of later materials referred 

 to Protoreodon pumilus, distinctly smaller than Diplobunops matthewi. 

 The teeth are in a stage of development comparable to that of Pro- 

 toreodon parvus, though possibly somewhat more primitive in being 

 perhaps lower crowned and more weakly crescentic. Its assignment 

 to Diplobunops, however, is based on the large size of the caniniform 

 teeth and their broad separation, although it should be noted that the 

 procumbent appearance of anterior cheek teeth in the lower jaw, as 

 seen in plate 9, may be largely due to crushing. Moreover, the upper 

 molars are, as in Diplobunops, significantly broad transversely, and 

 the low cusps are rather widely spaced across the crown. This is not 

 fully evident in plate 8 as there is marked foreshortening of the trans- 



MEASUREMENTS IN MILLIMETERS OF DENTITION IN TYPE SPECIMEN OF 



Diplobunops vanhouteni, p.u. no. 14251 



Length of upper cheek tooth series, C (at alveolus) -M', inclusive 78.5a 



Length of upper cheek tooth series, P'-M^, inclusive 65.00 



Upper premolar series, P^-P*, inclusive 34-Oa 



Upper molar series, M'-M', inclusive 3i-9 



C, anteroposterior diameter (at alveolus) : greatest transverse diame- 

 ter 9-00 : 8.5a 



P*, anteroposterior diameter 8.0a 



P°, anteroposterior diameter lo.o 



P', anteroposterior diameter 9-0 



P*, anteroposterior diameter : transverse diameter* 8.0 : 11. 9 



M*, anteroposterior diameter : transverse diameter* 9.4 : 12.2 



M', anteroposterior diameter : transverse diameter 10.9: 14.4 



M', anteroposterior diameter : transverse diameter 12.1 : 16.0 



Length of lower cheek tooth series, Pi (at alveolus) -M3, inclusive... 70.9 



Lower premolar series. Pi (at alveolus) -P*, inclusive 35-4 



Lower molar series, M1-M3, inclusive 36.1 



Pi, anteroposterior diameter: greatest transverse diameter (at alveo- 

 lus) 9-2 : 6.5 



P2, anteroposterior diameter : greatest transverse diameter 9-5 : 3-7 



P3, anteroposterior diameter : greatest transverse diameter lo.i : 5.1 



P4, anteroposterior diameter : greatest transverse diameter 10.5 : 6.2 



Ml, anteroposterior diameter : transverse diameter of talonid 9.4 : 7.8 



Ma, anteroposterior diameter : transverse diameter of talonid 10.3 : 8.4 



Ms, anteroposterior diameter : transverse diameter of trigonid 17.1 : 8.3 



a. Approximate. 



* Measurements of posterior upper premolars are taken anteroposteriorly across outer por- 

 tion and transversely perpendicular to outer margin. Those of upper molars _ are taken 

 anteroposteriorly perpendicular to anterior margin and transversely across anterior portion 

 of tooth. 



