544 



THE MAM:mALIA of the UINTA FORMATION. 



Ill forming " alternating " lateial contact with the magnum and unciform respectively. 

 Kovvalevskj, however, desciibes mc. iii as spreading jjosteriorly beneath both the 

 trapezoid and unciform. Thus the spreading of the magnum has already oftset the 

 progress of the more primitive displacement. A farther step is seen in HqfjJCirion. 



If De Blainville's figures are correct ((r. etjiius) the recent species, £J. caballus, 

 E. Burcliellii and E, asinus, present three stages in the growth of the magnum be- 

 neath the lunar. In the former there is a broad contact hetwocn the lunar and unci- 

 form, much as in Eipparion; in the latter there is none at all, the lunar resting wholly 

 upon the magnum, as in the pi-Imitive serial type. 



/'h 



eruu 



Pholo. 



yp 



ama,r.- 



A/esoh- 



Anch"' 



Hi 



n- 



i^.- 



DiAG. 10.— The evolution of Uic astnigalar and calcaneal facets in the Hyi-acothcriiim-IIipparion series. . Phenaco- 

 dmprimaviis. Cope collection ; Ilyracolheriam ventieolum. Cope collection; PUolopJius (Oioliippus) major, Princeton 

 collection; P. (Triplopus) amf/ron^ra, Cope collection ; MesoJdppus, Princeton collection; A7ichithtrium aurelianense, 

 Princeton collection ; Uipparion meditcrraneum, Princeton collection. The upper row represents the distal view of the 

 astraijalus and calcaneum ; the middle row the posterior view of the astrairahis ; the lower row the anterior view of 

 the calcaneum. a', a", a'", octal, sustentacular and inferior astragalo-calcaneal facets, c', c", c'", ditto calcanco- 

 astrajralar facets. ch,fb, n. cuboidal, fibular and navicidar facets upon astragalus and calcaneum. f, fossa in the 

 astrasalo-navicular facet. 



The reduction of the metacarpals is too familial- ground to require description 



here. 



Tarsus. In the tarsus we fortunately have a complete series from Hyracotherium 

 upwards. "We hegin with a tridactyl pes, although in the Wasatch species 77. 



