310 University of California Ptiblications in Geology \yoh. 12 



sharper than in the P. proversus tooth, while the anteroposterior length 

 of the column is about the same. 



Compared with Equus idahoensis Merriam" (type and referred 

 specimens, consisting of a worn and Mi from the Payette and Snake 

 rivers, Idaho), E. bauiistensis grinders are fully as specialized. The 

 upper teeth are of nearly equal size; the transverse thickness of the 

 protocone of P- of E. bautistensis with its deeply indented inferior 

 border somewhat suggests the premolar of E. idahoensis. Points of 

 difference are: (1) the anterior projection of the protocone in P- of 

 E. bautistensis (of series no. 23244) is more pronounced than in the 

 E. idahoensis P- of the same stage of wear; (2) the large complicated 

 lakes show no similarity to the narrow, simple, bordered fossettes of 

 the worn Idaho P-, but, on the other hand, somewhat resemble those 

 of the less worn Idaho M^, which, in turn, are relatively narrower 

 and more complicated than those of the Rancho La Brea form ; and 

 (3) the jDOst-protoconal valleys average broader throughout in the 

 E. bautistensis teeth. 



A wide range of characters is shown in Eejuus stenonis^'" as fig- 

 ured by Dr. C. J. Forsyth Major. The Bautista specimens, however, 

 are: (1) considerably larger than any illustrated under E. stcnonis; 

 (2) their protocones, while somewhat resembling those shown in figure 

 1 of Dr. IMajor's plate, are shorter and much less produced anteriorly 

 than those in his other figures; and (3) their lake borders are less 

 complex than those of the illustrated teeth (excepting in the case of 

 a worn series, figure 2 of the same plate, where the lakes of E. stenonis, 

 as might be expected, are less plicated than in the moderately worn 

 teeth of E. bautistensis) . 



Equus sivalensis'^'^ as figured by Dr. Lydekker suggests a stage of 

 development similar to that of E. bautistensis in both the size of the 

 teeth and the amount of folding of the fossette borders, as well as in 

 the degree of anteroposterior elongation of the protocone. The length 

 of the protocone shown in E. namadicus, on the contrary, would 

 indicate a considerably more advanced stage. 



Summary. — The dentition referred to Equus bautistensis in the 

 summation of its character may be said to be of an advanced early 



1* Merriam, John C. New Mammalia from the Idaho Formation. Univ. Calif. 

 Publ., Bull. Dept. Geol., vol. 10, pp. .523-530, 1918. 



15 Major, C. J. Forsyth. Beitrage zur Geschiehte der fossilen Pferde inbe- 

 sonders Italiens. Abh. sehweiz. palae. Ges., vol. 4, pt. 1, 1877. 



isLvdekker, K. Palaeontologia Indica, ser. 10, vol. 2, pt. 3, pis. 14, 15, 1882; 

 Eecord'Geol. Surv. India, vol. 43, pt. 4, 1913. 



