1921] Friclc: Faunas of Bautista Creek and San Timoteo CaTion 383 



limb material were never closely associated, each of the three is con- 

 sidered in a separate division. The writer has divided the upper teeth 

 into two main groups, and tentatively the lower teeth into two corre- 

 sponding groujos, as follows : 



Upper Cheek Teeth 



(1) Group of PUoliippus oshorni. — A group (see descriptions 

 below) in which the specimens exhibit strong E quits character, in the 

 marked anterior projection of the protocone and the grooving of its 

 inner margin, a degree of this anterior projection being retained in 

 even much worn teeth. Two forms are recognized: (1) PUoliippus 

 oshorni, n. sp. ; and (2) P. oshorni, subform A. The distinction 

 between the two, however, which is mainly one of size, may be sexual. 

 This group apparently represents an important and unrecognized 

 transitional stage in equine development. Somewhat similar but more 

 Equus-\ike teeth have been noted in the overlying beds (see figs. 38a- 

 38h, 39a-396, PUoliippus franeescana minor, n. subsp.). 



(2) Group of Pliohippus edensis. — A more typical PUoliippus 

 group (see description, p. 388), in which in moderately worn teeth 

 the protocone is narrow and baekwardly directed and in which in 

 aged teeth the protocone tends to thicken and to become more oval 

 in cross-section. Three forms are recognized: (1) PUoliippus edensis, 

 n. ,sp. ; (2) P. edensis, subform A, suggesting P. spectans Cope of the 

 Rattlesnake; and (3) P. edensis, subform "B. At the end of the group 

 are listed certain indeterminate teeth, including those of the milk 

 series. 



PLIOHIPPUS OSBOENI, n. sp. 



Type. — A large moderately worn upper cheek tooth from the right side, Univ. 

 Calif. Coll. Vert. Pal. no. 23787 (figs. lOSa-lOSf, 129), Univ. Calif, loc. 3269. 



Bef erred specimen. — A large third upper molar, Univ. Calif. Coll. Vert. Pal. 

 no. 23338 (figs. 104a, 104b), same locality. 



Characters. — The strong tendency towards the Equus rather than 

 the PUoliippus type, as shown by the elongated anteroposterior and 

 thick transverse diameters of the protocone, together with the broad 

 production of the anterior corner of the protocone and the indentation 

 of its inner margin. A corresponding equine flatness of the outer 

 walls of the protoconid and hypoconid is noticed in certain of the 

 lower teeth occurring in the same beds (see figs. 127 and 128). 



