1915] Merriam: New Species of the Hipparion Group 



7 



may have attained a length considerably greater than that normal in 

 Merychippus. Both crowns are heavily cemented at the summit. The 

 metaconid-metastylid column is longer anteroposterior^ than in any 

 Merychippus form known to the writer and corresponds in this diam- 

 eter to the dimensions of the column in species of the Hipparion group. 

 The groove between metaconid and metastylid is wide and flat as in 

 Hipparion, rather than narrow and sharp as is commonly the case in 

 Merychippus. The parastylid extends inward as far as the inner 

 border of the metaconid. A sharp anteroexternal ridge is developed 

 on the protoconid. The valleys anterior and posterior to the meta- 

 conid-metastylid column are comparatively narrow transversely, owing 

 to the large size of the metaconid and metastylid. These valleys cor- 

 respond approximately in size to those commonly seen in Hipparion, 

 and are narrower than those in most species of Merychippus. The 

 entoconid is large and unusually full on the anterointernal side. In 

 Merychippus this region of the entoconid is commonly not as well 

 developed and may be truncated obliquely. In Hipparion this region 

 of the entoconid is commonly full and the anterointernal angle is 

 nearly a right angle, as in the Ellensburg specimen. 



The fragment representing the symphysial region of the lower jaw 

 with the incisor teeth (no. 668, Univ. Oregon) is from an animal not 

 differing greatly in dimensions from a number of Merychippus speci- 

 mens from the Upper Miocene of the Barstow region. The incisors 

 are considerably worn, but still show the inner enamel rings of the 

 pits. No satisfactory material representing this portion of the adult 

 dentition of Merychippus from the Mascall Miocene is available for 

 a comparison. The teeth are in general larger than those of Mery- 

 chippus calamarius of the Barstow Miocene and are much smaller than 

 incisors of a large Hipparion from Ricardo. On tin- somewhat worn 

 crowns shown in figure 5 the enamel invaginations are clearly shown 

 on all three teeth. The incisors were evidently deeply clipped, but 

 this condition obtains also in the incisors of Merychippus, although 

 the infolding of the enamel on the third lower incisor of Merychippus 

 is much less strongly marked than on the Ellensburg specimen. 



The stage of advance shown by the cheek-teeth of the Ellensburg 

 specimen seems to the writer to be that of Hipparion rather than that 

 of Merychippus. The form represented in no. 672 does not correspond 

 exactly to any species known to the writer and may be designated as 

 a new species, Hipparion condoiii. It is distinguished by the size of 

 the crown and by the size and form of the metaconid-metastylid 



