1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 553 



small antero-extcrnal fold. Several other specimens from the Ricardo 

 show approximately the characters seen in this type. 



The Ricardo specimens exhibit considerable variation in size and 

 form. The extremes of difference are probably those separating the 

 type specimen from the complete dentition represented in no. 21311 

 described below as Hipparion mohavense mllodonte. The gaps are 

 partly bridged, but it is not improbable that two or more distinct 

 species are represented. 



HIPPAEION MOHAVENSE CALLODONTE Merriam 

 Figures 171 to 175 



H. m. caltodonte Merriam. "Univ. Calif. Publ., Bull. Dept. Geol., vol. 9, 

 p. 54, figs. 5-7, 1915. 



Type specimen no. 21311, a practically complete upper and lower dentition 

 from locality 2281, in the upper portion of the Eicardo Pliocene, near Eicardo 

 Post Office, California. 



A finely preserved specimen (no. 

 21311, figs. 171-175) representing all of 

 the elements of the cheek-tooth denti- 

 tion, and several incisors was discovered 

 by E. M. Butterworth in 1913. This 

 specimen shows the dentition very slight- 

 ly worn, with M 3 not yet in function. 

 The upper cheek-teeth are slightly larger 

 than those of the Hipparion mohavense 

 specimen no. 21320. The protocone 

 shows more marked transverse flatten- 

 ing, the enamel pattern exhibits more 



numerous folds, but fewer which are deep and well rounded. Much 

 of the difference to which attention has just been directed is evidently 

 due to the fact that the teeth of H. m. calloclonte are in a less advanced 

 stage of wear. The difference in complication of the enamel folds 

 may not be explained on this basis. - 



In specimen 21311 the complete lower cheek-tooth series is present 

 with the upper series. P 4 shows incipient wear; M 3 was not yet in 

 function. These teeth represent an individual somewhat larger than 

 the type specimen of mohavense. The enamel is markedly folded, 

 though not as strongly as in some specimens of H. gracile. 



Incisor teeth associated with specimen 21311 (figs. 174, 175) show 

 a strongly developed cupping of the enamel. 



Pigs. 171 to 175. Hipparion 

 ■mohavense callodonte Merriam. 

 Incisor teeth, no. 21311, natu- 

 ral size. Eicardo Pliocene, 

 Mohave Desert, California. 



