1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 573 



cuneiform is not separated as a distinct lunate facet as in no. 21198, 

 but is connected with the anterior portion of the articulation at its 

 inner or medial end. 



Metatarsal IV is shown complete in no. 21475 (fig. 204). It is 

 considerably shorter and heavier than in Neohipparion whitneyi. The 

 distal end has a large facet for support of a phalanx. This specimen 

 evidently belongs with a metatarsal III as large as that seen in 

 no. 21198. In no. 21476, a metatarsal IV is seen associated with a 

 metatarsal III apparently of the same type as that in no. 21198. In 

 no. 21476, the proximal end of metatarsal IV is somewhat thinner 

 than in 21475 and the proximal articulation with the cuboid is divided 

 into two facets instead of being a single facet, as shown in no. 21475.' 

 This difference may have some significance in specific or generic 

 diagnosis or may be merely individual. 



Metatarsal II is seen in no. 21479 (fig. 205). It is much smaller 

 than metatarsal IV. There is no evidence indicating the presence of 

 metatarsals I and V. 



A single specimen, no. 21480 (fig. 201), seems to represent a 

 metatarsal IV nearly twice the size of the other specimens from the 

 Ricardo region. It differs from those of the large horses in the 

 marked concavity of the surface of articulation for the cuboid. This 

 surface curves upward sharply to the summit of a sharp spine or 

 prominence on the inner side of the proximal end of the bone and 

 immediately behind the facet for articulation with metacarpal III. 

 There is also a possible difference from metatarsal IV of the horses 

 described in the absence of a posterior inner face for articulation 

 with metatarsal III. The relationship of this specimen is uncertain. 



The equid astragali from the Ricardo region are larger than any 

 from the Barstow excepting a large Barstow specimen presumably 

 representing Hypohippits. Of the specimens available for comparison 

 the Ricardo astragali most nearly resemble certain specimens from 

 the Thousand Creek Pliocene which represent a Pliohippus or a 

 Hipparion-like form. The range in size among the Ricardo astragali 

 is considerable (figs. 208-210), and it is probable that two species 



Fig. 206. Pliohippus?, sp. Distal end of metapodial, no. 22325, X %. 

 Kicardo Pliocene, Mohave Desert, California. 



Fig. 207. Pliohippus or Hipparion, sp. Cuboid, no. 21198, inner view, X %. 

 Ricardo Pliocene, Mohave Desert, California. 



Figs. 208 and 209. Pliohippus or Hipparion, sp. Astragali, X %. Fig. 208, 

 no. 21495 ; fig. 209, no. 21213. Eieardo Pliocene, Mohave Desert, California. 



Fig. 210. Hipparion or Pliohippus, sp. Astragalus, no. 22326, X %. Ricardo 

 Pliocene, Mohave Desert, California. 



