THE MAMMALIA OP THE DEEP RIVER BEDS. 109 



occurs in A. aurelianense, though the latter species displays a considerable degree of 

 variation in this regard. In the specimen figured by Kowalevsky the ungual is very 

 long, depressed, and pointed towards the distal end, and yet with considerable dorso- 

 palmar depth. Gaudry's figure of the same species exhibits a decidedly more mod- 

 ernized hoof, marked by the more rounded border of the palmar surface, the greater 

 vertical depth and consequent steeper inclination of the anterior face; the proximal 

 articular facet is much more nearly parallel to the plane of the palmar surface. A 

 third type of ungual which has been referred to this species is shown in Fraas' figures 

 of the large animal from Steinheim. Here the anterior border of the palmar surface 

 is more regularly rounded than in Kowalevsky's specimens, except for the more con- 

 spicuously marked emargination in the median line and the groove which runs proxi- 

 mally up the median line of the anterior face of the bone from this emargination. 

 The phalanx is narrower in proportion to its length and the facet for the second pha- 

 lanx is very steeply inclined to the plane of the palmar surface than in either of the 

 French t} r pes, and apparently the bone is more depressed than in the latter. Part of 

 the difference between Kowalevsky's and Gaudry's figures may be due to the fact 

 that the former is of the hind foot and the latter of the fore foot, but this assumption 

 would not account for the Steinheim type, which is different from both. 



The ungual phalanx of A. equinum is decidedly more like the Steinheim type 

 than either of the French ones, and differs from it principally in the better develop- 

 ment of the " basilar processes " and " wings " and in the less deep lateral constric- 

 tions of the bone below the proximal head. 



Hind Limb. The pelvis is very like that of MesoMppus, except in size, and 

 approximates the modern type but little more than does that of the White River 

 genus. As compared with the pelvis of the horse, the neck or shaft of the ilium is 

 much longer, the plate less expanded and everted, and the gluteal surface less con- 

 cave; the pit for the origin of the rectus femoris muscle is smaller, deeper, and much 

 nearer to the acetabulum. The iliac surface is rather narrower and the pubic border 

 less promiuent than in MesoJrippus. The acetabulum has prominent margins and the 

 sulcus for the round ligament is less extensive and narrows the articular surface less 

 than in Equus ; it has the peculiarity that the end of the sulcus, where the anterior 

 and posterior borders meet, is angulate instead of curved. The ischium is straighter 

 and more slender, the obturator foramen very much larger and more oval, and the 

 descending plate of the ischium much less expanded than in the modern form. The 

 supra-acetabular crest is but feebly developed and the tendinal sulci not deeply cut. 

 The pubis is likewise more slender and less rugose than in Equus. Little is known 

 of the pelvis in A. aurelianense, but the fragments preserved show an important dif- 



