458 THE WASATCH FAUNA. 



Measurements of tibia and fibula, 



11. 



Total length of tibia 210 



{ anteroposterior at internal cotylus 048 



Diameters of head^ anteroposterior at popliteal notch 034 



' transverse 1.. .055 



Anteroposterior width of shaft at distal third 020 



Diameter distal end tibia ^'"'**™P''^'«""'(S'"«'^**«*) "33 



( transverse 032 



Length fibula 186 



Proximal diameter ^'^'^^^'■"P"**''"'"" 02"^ 



( transverse Oil 



Diameter of shaft Oil 



Distal diameter 5 ''°*«'"''P««*''"*"" 025 



i transverse 019 



As compared with the tibiae of Hyracotherium venticolum and Hyrachyus 

 agrestis, that of the Phenacodus primcevus displays its simplicity in the 

 absence of the notch of the anterior external border of the head and of the 

 tuberosity which, especiall}' in the H. agrestis, bounds it in front. The distal 

 extremity agrees with that of the Hyracotherium in being in the same plane 

 as the head, but it diifers from both the species in the large flat malleolus. 

 In the Perissodactyla named, it has a small anteroposterior extent, and its 

 extremity is widely beveled in a fashion not seen in the Phenacodus. 



The posterior foot is one-half longer than the anterior foot. The cal- 

 caneum and astragalus are about the size of those of Hyrachyus agrestis, but 

 the median toes are a little shorter. The trochlea of the astragalus is about 

 the size of that of the last-named species, but the groove is not so deep nor 

 so wide. The head is nearly as Avide as the trochlea, and its face is in front 

 of the inner two-thirds of- the latter, and extends in front of the malleolus 

 of the tibia. Its anterior and external outlines viewed from above form a 

 regular curve, a segment of a wide ellipse, to the line of the front of the 

 trochlea, where the outline contracts abruptly. The navicular articular 

 face is wider than deep, and is turned somewhat under. Superior face of 

 head flat. There is no deeply-impressed fossa on either side of the trochlea 

 of the astragalus as in Hyrachyus, etc. The calcaneum has much the shape 

 of that of Hyrachyus agrestis, but is more robust. The sustentaculum is 

 much more massive, having the vertical sides and a flat inferior face of 

 equal width. The cuboid facet is transversely diamond-shaped, nearly as 

 deep as wide, and without notch near the astragalus. There is a quite 



