1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 575 



The nature of the lateral metapodials in the Kicardo specimens 

 can be nearly duplicated in Hipparion of the Old World or in Proto- 

 hippus or Pliohippus of America. 



A cuboid, no. 21204, from the Ricardo differs from that of 

 Hipparion as figured by Weithofer mainly in the separation of the 

 posterior facets for navicular and ectocuneiform. In Hipparion, as 

 shown by Weithofer, these facets are contiguous as in E quits. This 

 specimen differs from the cuboid in the Barstow Merychippus forms 

 in the position of the posterior facet for the navicular somewhat 

 nearer the proximal end of the element, and in its slightly less 

 prominent tuberosity. 



OREODONTIDAE 



MEBYCOCHOEBUS? (PBONOMOTHEBIUM?) CAL1FOBNICUS, n. sp. 



Type specimen, no. 21351, a fragmentary skull with molar dentition, from 

 locality 1755, Bicardo beds, Mohave Desert, California. 



A large, highly specialized oreodont is represented by the type 

 material and several other more imperfect specimens from the beds 

 near Ricardo. So far as known this form is one of the largest and 

 most highly specialized of the oreodonts. Its characters are near those 

 of Merycochoerus and approach those of the bizarre Pronomotherium 

 from the Madison Valley beds of Montana. 



The skull is very badly crushed, but shows some of the general 

 outlines. It seems short and the facial region appears depressed. 

 The orbits are small. The zygomatic arch is deep below the orbit, and 

 is widely expanded. The occipital region (fig. 211) is extremely 

 wide as in Merycochoerus. The widely spreading mastoid plates 

 merge into the heavy paroccipital processes below. The sagittal crest 

 is low. The palate is wide ; the processes are relatively heavy and 

 project relatively far inferiorly. 



The premaxillaries are closely united with the maxillaries, and 

 the superior margin of the premaxillaries slopes backward at a low 

 angle indicating a low, wide anterior nasal opening. The infra- 

 orbital foramen is situated over the anterior region of M 1 . 



The cheek-teeth are large and seem to show a very advanced stage 

 of development in relative length of the molar series, in hypsodonty, 

 and in complication of the premolars. 



The molars are large, the crowns are long, and the styles promi- 

 nent. The internal cingulum is faint on the type specimen, but is 

 strongly marked on no. 21353 (fig. 214) from the Ricardo beds. The 



