FOSSIL HORSE REMAINS FROM IDAHO — GAZIN 289 



of Texas and Pliohippus proversus Merriam ^^ from the upper Etche- 

 goin in the Coahnga region of California. P. simplicidens was orig- 

 inally described as a species of Equus but later referred by Gidley ^^ 

 to Pliohippus. The intermediate character of the teeth in these 

 forms between Pliohippus and Equus as noted by Merriam and addi- 

 tional characters exliibited in the skeletons collected by Matthew 

 and Simpson in the Blanco beds formed the basis for the genus 

 Plesippus. A third species, Equus cumminsii Cope,-" also from the 

 Blanco, was later included by Matthew and Stirton ^^ in Plesippus. 

 This species was early referred to Protohippus by Gidley ^^ and then 

 to Pliohippus by Merriam ^^ and by Osborn.-* In 1930, Gidley ^^ 

 described the equid material from Hagerman to which he gave the 

 name Plesippus shoshonensis. Subsequent finds of equid material 

 that have been referred to Plesippus mclude teeth identified by 

 Vander Hoof -'^ as Plesippus proversus from the Tehama beds in 

 California. 



Mammalian material described by Frick " in 1921 from the San 

 Timoteo Hills near the San Jacinto Mountains in southern California 

 included equid specimens referred to Pliohippus, which may well 

 represent Plesippus. Material designated as Pliohippus francescana 

 and perhaps that named Pliohippus osborni appear from the illustra- 

 tions to represent a stage of development comparable to that in 

 material elsewhere referred to Plesippus. 



CHARACTERS OF THE GENUS PLESIPPUS 



The characters outlined by Matthew as defining the genus Plesippus 

 are for the most part intermediate between those of Pliohippus and 

 of Equus. With the accumulation of additional evidence showing the 

 continuity from one genus to another, recognition of the limits of 

 these genera necessarily becomes more arbitrary and perhaps ques- 

 tionable. The following diagnosis of Plesippus is taken from Mat- 

 thew's ^^ description of the Blanco material that he referred to Ple- 

 sippus simplicidens: 



" Merriam, J. C, Univ. California Piibl. Bull. Dept. Geol., vol. 9, no. 18, pp. 525-534, 1916. 

 »9 Gidley, J. W., Bull. Amer. Mus. Nat. Hist., vol. 14, art. 9, pp. 123-125, 1901. 

 2" Cope, E. D., 4th Ann. Rept., Geol. Surv. Texas, 1892, p. 67, 1893. 



21 Matthew, W. D., and Stirton, R. A., Univ. California Publ. Bull. Dept. Geol. Sci., vol. 19, no. 17, 

 pp. 359, 367 (tables), 1930. 



22 Gidley, J. W., Bull. Amer. Mus. Nat. Hist., vol. 14, art. 9, pp. 126-127, 1901. 



23 Merriam, J. C, Univ. California Publ. Bull. Dept. Geol., vol. 9, no. 18, pp. 526-527, 1916. 

 21 Osborn, H. F., Mem. Amer. Mus. Nat. Hist., new ser., vol. 2, pt. 1, pp. 168-169, 1918. 



25 Gidley, J. W., Journ. Mamm., vol. 11, no. 3, pp. 300-303, 1930. 



28 Russell, R. D., and Vander Hoof, V. L., Univ. California Publ. Bull. Dept. Geol. Sci., vol. 20, no. 2, 

 pp. 17-21, figs. 4-6, 1931. 

 2' Frick, Childs, Univ. California Publ. Bull. Dept. Geol., vol. 12, no. 5, pp. 277-424, 1921. 

 28 Matthew, W. D., Amer. Mus. Nov., no. 131, p. 2, 1924. 



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