10S 



osborn: OLIGOCENE, MIOCENE, pliocene equid^e. 



protoconule in molars one-fourth worn; (4) protocone elongate anteroposteriorly in p 4 -m 3 ; (5) metaloph sending a single 

 fold into prefossette, and from one to two folds into postfossette; (6) shafts of limbs robust; (7) metapodials robust; 

 (8) shafts of lateral digits and lateral phalanges much heavier than in M. isoncsus secundum and M. isoncsus tertius. 



Merychippus sp. Sellards 1916. 

 Text Fig. 82. 



Merychippus sp., Sellards, E. H. "Fossil Vertebrates from Florida: A New Miocene Fauna; New Pliocene Species; The Pleisto- 

 cene Fauna," Eighth Ann. Rept. Florida State Gcol Surv., 1916, pp. 87-88, PI. 11, fig. 1, PI. 13, fig. 6. 



Horizon and locality. — (Sellards, pp. 87-88) " In 1908 the writer obtained from the fuller's earth mine at Quincy a 

 single lower cheek tooth of Merychippus. The specimen was secured from a workman who found it while digging with a 

 pick in the indurated sand above the fuller's earth stratum. Further evidence of its place in the deposit is afforded by 

 the fact that the base of the tooth contained the gray sand characteristic of the Alum Bluff formation." 



Fig. 82. Merychippus sp. Sellards. (Left figures) Fla. Surv. Coll. 173, type, lower cheek tooth; (upper) side view 

 from photograph, PI. 11, fig. 1, (lower) crown view, drawing, PI. 13, fig. 6. (Right figures) Fla. Surv. Coll. 7527, lower 

 cheek tooth, a referred specimen; (upper) side view, PI. 13, fig. 5, (lower) crown view, PI. 13, fig. 4. All figures natural size. 

 After Sellards, 1916. 



Type. — (Sellards, p. SS) " The specimen is No. 173 of the Florida Survey collection . . . The species is no doubt new 

 although it is desirable to secure additional material to serve as a type before naming the species." Measurements: (Sel- 

 lards, p. 88) "Greatest anteroposterior length, 17 mm.; width 7 mm." 



Type figure. — Text Fig. S2 of this Memoir. 



Characters. — (Sellards, p. 88) "The tooth, as may be seen by the illustrations, is moderately hypsodont and has a 

 coating of cement. The metaconid and metastylid are distinctly separated. The tooth is but little worn and may be 

 referred with confidence to the genus Merychippus. Professor J. C. Merriam, who has compared this tooth with the horses 

 of the western United States contained in the University of California collection, has kindly-supplied the following notes: 



'Your tooth, No. 173, most closely approaches the lower dentition of one of our horses from the recently discovered fauna occurring 

 in beds crossing the summit of the Southern Sierra of Tehachapi. One of these species I have considered the most primitive known 

 Merychippus . . . .1 will say in conclusion that your specimen No. 173, is very much more progressive than any Oligocene horse known to 

 me. It is certainly very different from our uppermost John Day horses. Your specimen is also more progressive than any horse cer- 

 tainly referred to the lower Miocene of North America. Our fauna from the Tehachapi is presumably middle Miocene, but it might 

 possibly be the uppermost portion of the lower Miocene. I should judge that the horizon from which tooth No. 173 came is somewhere 

 near the lower portion of the middle Miocene, unless there is a very unusually advanced type in an old formation or an unusual survival 

 of an old form in a late formation.' " 



MERYCHIPPUS PANIENSIS-M. SEJUNCTUS ZONE. 10. LATE MIDDLE MIOCENE. 



This zone is typified at Pawnee Creek, Colorado, and contains numerous species of Merychippus. 



