1889.] 455 [Cope. 



the tibia of the latter, although the sizes of the crowns of the teetli in the 

 two species is about the same. The crest is narrower and more prominent 

 than that of tlie horse and quagga, and similar to tliat of the A. prcestans. 

 It differs from that of the latter in the entire coossification of the distal 

 extremity of the fibula and entire absence of the splint-like shaft seen in 

 the adult A. prcestans. The spine is well marked and widely divided, and 

 the external anterior notch is deep. The popliteal fossa is well marked. 

 Tlie shaft is flattened from side to side, and presents an obtuse edge out- 

 wards along the middle of its length. It is not marked by muscular and 

 other impressions as in AncMtJieriam prcestans. The distal end is much 

 like that of the species just named ; both difi'er from those of the horse 

 and quagga in having the internal tuberosity of a more oblong form and 

 less prominent. 



Mensurements of Tibia. 



M. 



Total length 3">3 



Diameters of head 



anteroposterior 047 



transverse 060 



■r». . r •111 c 1 r^ ^ anteroposterior 030 



Diameters of middle of shaft ] ^ 



c transverse 028 



Diameters of distal extremity S^'^'^'"«P''^^^"«^ ^''^ 



c transverse 041 



The tarsus is represented by calcaneum, astragalus, navicular and ecto- 

 cuneiform. The first two do not differ from the corresponding bones of 

 an undetermined Protohippus beyond their somewhat smaller size, ex- 

 cepting in the better developed calcaneal facet on the external margin of the 

 astragalus. The astragalus agrees with that of the undetermined Proto- 

 hippus, and differs from that of the horse in three points : (1st) The less 

 extension inward of the distal tuberosity and navicular facet ; (2d) the 

 greater compression of the trochlear keels ; (3d) the distinct extension of 

 the prominent inferior margin of the internal superior trochlear smooth sur- 

 face, to the internal distal tuberosity. The quagga is intermediate in these 

 points. The facets of both surfaces of the navicular are not so much sub- 

 divided as in the horse, but more so, as to the upper surface at least, than 

 in the A/ichitherium preestans. Its anterior portion is not so expanded out- 

 wards as in the horse, but is considerably more so than in A. prcestans, and 

 about as in Protohippus. The same statements apply to the ectocuneiform. 

 The superior facets are divided as in the horse, but inferiorly the posterior 

 facet is a branch of the anterior, not distinct from it as in the living 

 species. 



Measurements of Tarsus. 



M. 



Length of calcaneum = .070 



" " sustentaculum 049 



Greatest width of calcaneum 030 



Depth of sustentaculum at middle 028 



