394 University of California Publications in Geology [Vol. 12 



and especially of the hypoconid are, as above noted, unusually flat 

 for Pliohippus. The fold between the protoconid and hypoconid 

 extends in the form of a fine line within the mouth of the metaconid- 

 metastylid, suggesting such a development and extension in the molars 

 as is alone seen in the lower molars of the following section and in 

 those of Pliohippus francescana of the overlying beds. The entoconid 

 is very large and full. The specimen is very tentatively referred to 

 the large upper tooth described as Pliohippus osborni no. 23787 

 (figs. 129, 1030^103/). 



Second specimen (no. 23197, fig. 128). — This tooth is long-crowned, 

 of large size, and of exceptional proportions, the triturating surface 

 being long anteroposteriorly and very narrow transversely. The 

 M'ings of the metaeonid-metastylid column are widely extended, the 

 gutter is deep, and the exterior faces of the hypoconid are relatively 

 flat, both protoconid and hypoconid being very narrow transversely. 

 The specimen is evidently a molar. In character it is very like the 

 larger specimen (no. 23222, fig. 127), excepting for its narrowness, 

 though fully as great a reduction in the transverse breadth of the 

 molars over the premolars at times is known to occur. The two teeth 

 may represent the same species. 



Measukements of Pliohippus osborni 



Premolar 

 no. 23222 



Anteroposterior diameter of crown 28.3 mm. 



Transverse diameter of crown 14.3 



Anteroposterior length of metaeonid- 



stylid column 16.6 



Referred 



molar 

 no. 23197 



27.7 mm. 



10.6 



14 



LOWER TEETH, TENTATIVELY REFEEEED TO PLIOHIPPUS OSBOENI, 



subform A 



Material. — A section of the mandible from the right side containing Pj, Mj, 

 Mj, and M5, Univ. Calif. Coll. Vert. Pal. no. 23510 (fig. 131), Univ. Calif, loc. 

 3269. An Mj with attached portion of P3 and an associated portion of Pa, Univ. 

 Calif. Coll. A^ert. Pal. no. 23286 (fig. 130); the fragment of a mandible with Pj 

 and P5, no. 24040. Both from the same locality as the type. 



Characters. — Proportionately great anteroposterior extension of 

 the metaeonid-metastylid column and openness of the gutter; the 

 presence of a small accessory fold at the anterior inner corner of 

 the protoconid in M^; the large size of as compared to P^; the 

 deep, evenly concave, versus angularly convex, outer margin of the 



