238 



University of California Publications. 



[Geology 



summit. In P. cognatus it is completely separated by a deep 

 groove extending to the base of the crown. ^ 



Measurements. 

 Diameters of ?>/], anteropost. 22 mm., transv. 1/ mm. 

 Diameters of dp u anteropost. 9.5 mm., transv. 6.5 mm. 

 Diameters of dp„, anteropost. 24 mm., transv. 14 mm. 

 Diameters of dp t , anteropost. 24 mm., transv. 15 mm. 

 Length of milk-molar series, dp, to dp^ 71 mm. 

 Depth of jaw at dp lt 42 mm. 



MERYCHIPPUS ISONESUS (Cope). 



A right upper molar (no. 10670, Univ. Cal. Col. Vert. Palae.) 

 agrees in size and general characters with the corresponding tooth 

 in the type of M. isonesus, and may be referred provisionally to 

 that species. 



Diameters of molar, anteropost. 18 mm., transv. 22 mm. 



MERrCHIPPUS, sp. indet. (1). 

 Figs. 2 and 3. 



A second species of Merycltippus of an almost brachyodont 

 type is represented by two upper premolars, p 1 and p 2 , in a frag- 

 ment of the maxillary bone (no. 10659. Univ. Calif. Col. Vert. 



2 3 



Figs. 2 and 3. — Mevychippus, sp. indet. (1), first and second upper pre- 

 molars, no. 10659, natural size. 



Palae.) The p 2 has about the size and proportions of the corre- 

 sponding tooth in M. calimarius except that it is much lower 

 crowned. It differs from the latter also in some other important 

 respects. P 1 is much larger than that of M. calimarius, which it 

 exceeds by nearly one-half its anteroposterior diameter. It is 



