1913] 



Merriam: New Protohippine Horses 



439 



to the measurements given by Schlosser there is a suggestion that 

 the upper molars of richthofeni are slightly longer than in 

 the Mohave species. 



The Mohave form differs from Hippodactylus antilopinum 

 of India in the more clearly rounded enamel folds, and the longer 

 enamel fold on the inner wall opposite the protocone. It differs 

 from Hipparion theoboldi in its smaller size. 



Several lower cheek-teeth associated with the upper teeth 

 constituting the type specimen of Hipparion mohavense are pre- 

 sumably a part of the type specimen. The lower teeth are long- 

 crowned, but do not appear to have been unusually long previous 

 to wear. The antero-internal column formed by the metaconid 

 and metastylid is long anteroposterior^, and is divided on the 

 medial side by a deep, wide longitudinal furrow. The enamel 

 folds show a tendency to form secondary plications, especially 

 on the inner side of the parastylid ridge, and on the anterior 

 side of the hypoconid pillar. The small, sharp fold common on 

 the antero-external angle of the protoconid is seen in several 

 specimens. 



The form of the lower teeth is near that of certain of the 

 specimens of Hipparion richthofeni figured by Schlosser 5 and by 

 Koken. 6 The enamel folds in //. richthofeni are possibly a 

 little more pronounced, and the crowns a little longer, but the 

 discernible difference appears small. 



An upper cheek-tooth closely resembling the Mohave species 

 is known from the Coast Range region of California. This 

 specimen was recently referred to Hipparion or Neohipparion 

 by the writer. 7 It is interesting to note that a suggestion of 

 relationship of this tooth to Hipparion richthofeni was made by 

 Gidley in correspondence in 1904. The tooth had, however, been 

 labeled Neohipparion, and the recent reference to Hipparion by 

 the writer was presumed at the time the determination was made 

 to be at variance with that expressed by Gidley. 



s Op. cit., Taf. 4. 



6 Koken, E., Palae. Abh., Bd. 3, Taf. 4, 1885. 



t Merriam, J. C, Univ. Calif. Publ. Bull. Dept. Geol., vol. 7, p. 376, 

 and figs. 3a and 3b, p. 375, 1913. 



