Vol. 4] Sinclair. — John Day Rodents and Ungulates. 



137 



lesser tubercles. Mammilated external (singula appear on P 4 

 and the molars. Anterior and posterior cingula appear on I" 

 and the molars.. An internal cingulum is developed on P 3 and on 

 Ms 2 -\ On the latter teeth it is mammilated like the external 

 cingulum. 



The lower incisors have not been preserved. The canine is 

 triangular in cross-section with a prominent median ridge on the 

 outer side. P, is represented by a single large alveolus close to 

 the canine. P., is double rooted with a simple laterally com- 

 pressed crown. P. supports a small anterior basal cusp and a 

 moderately broad heel. On P 4 the protoconid and deuteroconid 

 are equally developed and separated by a deep notch. There 

 is a. broad heel with an antero-posterior ridge formed by tin 2 

 confluence of two small conules. The diastema between P, and 

 P„ is 6mm. in length. A somewhat shorter interval (5mm.) sep- 

 arates P ; and P.. Like those of the superior series, the lower 

 molars increase rapidly in size posteriorly. The heel on M 3 is 

 large, supporting a number of small cuspules, which vary in po- 

 sition in the same individual. External and internal cingula are 

 developed on the heel of P 4 and at the mouths of the transverse 

 valleys in the molars. Anterior and posterior cingula are pres- 

 ent on P 4 and the molars. In M., the greatly developed heel re- 

 places the posterior cingulum. 



The only other part of the skeleton known is the calcaneum, 

 a part of which was preserved in the matrix investing each of the 

 two crania. It is similar to the calcaneum of Dicotyles, but is 



considerably larger. 



Measurements. 



Length of cranium from anterior extremity of pre- No. 556 No. 1989 



maxilla to condyle inclusive 204 mm 



Interorbital width 84 



Depth of skull to alveolar border at front of orbit. 80 73.5 mm 



Width of palate at P 4 27 



Width of palate at middle of M 3 25.5 



Length P^M" inclusive 79.5 81.5 



Length Pj-ft'L, inclusive 96 



Length M*-M 3 inclusive 46 48 



Length M^M, inclusive 51 



P*, antero-posterior diameter 8.5 9 



P 4 , transverse diameter 9 12 



