324 University of California Publications in Geology [Vol. 12 



of wear as the worn Bautista series shown in folder 2, fig. 3). The 

 protoeone of P- and of P- in cross-section tends toward cylindrical 

 form, the inner border being without trace of the usual premolar 

 indentation, and the cusp strongly suggesting that of the more 

 primitive Pliohippus forms of the lower horizon. In the molars the 

 corresponding cusps are elongated and thick, with flattened inner 

 borders. The lack of anterior projection of the protoeone may be 

 studied in the series of sections of two of three referred unworn teeth 

 (folder 3, fig. 2). The degree of anterior projection of this cusp in 

 equine teeth is somewhat proportional to the stage of wear, the amount 

 of the same in the top section of a slightly worn molar being greater 

 than tliat in the lower section, so that the absolute amount of pro- 

 jection of the protoeone in the unworn section of the present form 

 may exceed that of the worn tooth of a more advanced equine, i.e., 

 Equus bautistensis. The postprotoconal valley is of moderate width, 

 narrowest in P- and in the molars, and has the usual accessory fold, 

 this being most prominent in the less worn teeth. It is absent in a worn 

 M-. The cement lakes in the premolars are long and broad, with short, 

 broad horns ; in the narrower molars they are more contracted and 

 the horns considerably elongated, resulting in a great curvature of 

 the adjoining borders of the paraeone and metacone, and accompanied 

 with an unusual angularity of the inner lake margins. The tip of 

 the anterior prong of the postfossette in the premolars lies superior 

 to that of the anterior fossette ; the two horns in the first molar occupy 

 nearly subequal positions. The margins of the more worn fossettes 

 are extremely simple, that of the posterior lake being nearly without 

 plications, and the anterior lake having but a small single fold in its 

 anterior and posterior walls ; in earlier stages the median wall of the 

 anterior fossette is somewhat plicated. 



The lower series and associated specimens referred to the type 

 are considerably worn. The teeth are of a large and very thickly 

 proportioned type. The wings of the metaconid-metastylid column 

 are broad and rounded in the premolars, and narrowed in the molars. 

 The groove of the metaconid-metastylid column is moderately deep, 

 sharp, and symmetrical rather than asymmetrical (see the propor- 

 tionately worn series from Bautista, fig. 19). The fold between the 

 protoconid-hypoconid is remarkably wide and deep, and in the molar 

 portion of the series is greatly produced within the expanded mouth 

 of the metaconid-metastylid column. The presence of a prominent 

 accessory infolding of the valley in less worn teeth is suggested by a 



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