428 University of California Publications in Geology [Vol. 7 



for doubt that the two jaws represent the same species. 



The species represented by specimens 19840 and 19764 seems 

 distinct from any form thus far described. In spite of its frag- 

 mentary nature, the upper jaw specimen is selected as the type, 

 as the characters of the superior cheek-tooth series seem more 

 significant in discussion of the relationships. 



Upper Cheek-teeth. — In the specimen representing the upper 

 jaw (fig. 3), the well-preserved, unworn, inner portion of M 1 

 offers good opportunity for examination of certain distinctive 

 characters of this form. In this tooth the metaloph is fully 

 united with the ectoloph. The protoconule is distinctly separate 

 from the protocone, it is considerably elongated and flattened, 



3 4 



Fig. 3. Parahippusf ? ) mourningi, n. sp. Dm', Dm 4 , and M 1 . No. 19840, 

 X I 1 /;. Mohave Miocene, Barstow Syncline, Mohave Desert, California. 



Fig. 4. Archaeohippus ultimus (Cope). Upper molar. No. 1689, X 1%. 

 Middle Miocene, Mascall Beds, Eastern Oregon. 



and its inner end slightly overlaps the protocone. The hypostyle 

 is larger than in Hypohippus and Archaeohippus, and there is 

 a more distinct cup-like depression behind it. There is no sug- 

 gestion of a crochet, though several plate-like projections arise 

 from the anterior side of the outer e^l of the metaloph. The 

 cingulum is well developed <>n the posterior side, and less dis- 

 tinctly on the anterior side between protocone and protoconule. 

 There is no shelf of the cingulum on the inner or lingual side 

 of the tooth. The cusps or ridges of the crown are somewhat 

 higher than in Archaeohippus or in Hypohippus. The surface 

 shows a degree of rugosity more pronounced than seems char- 

 acteristic of Hypohippus or of Archaeohippus. No trace of 

 cement is evident upon the crown. 



