108 THE MAMMALIA OF THE DEEP RIVER BEDS. 



different from that of the French specimens and, seen from the front, it is much 

 straighter and less arched outward than in Kowalevsky's figure. Gaudry, however, 

 represents it more as in the American species (No. 13, Fig. 176). I may add here that 

 the latter drawing shows a very much wider median metacarpal than in A. equinum, 

 hroader in proportion to its length than in Protdhippus or Hipparion. 



The second phalanx differs from that of the European species, especially in the 

 very much greater development of the posterior " salient beak," which is formed by 

 a prolongation of the external half of the proximal surface. This, together with the 

 more marked median constriction, gives the side view of the second phalanx quite a 

 different appearance in the two species. 



The lateral unguals are still more different. In the Sansan specimens of A. aure- 

 lianense "this phalanx is very small; it has the shape of a right-angled triangle, of 

 which the hypothenuse forms the postero-inferior border and the right angle is placed 



antero-superiorly It does not differ appreciably from the same phalanx of 



Hipparion" (Kowalevsky, p. 69). In A. equinum the ungual is much larger in 

 every dimension, especially in the length of the postero-inferior border; the so-called 

 "basilar process" and "wing" are also better developed, and the outline is that of a 

 spherical triangle, all of the borders being curved. In length this bone much exceeds 

 either of the other phalanges and must have had distinctly more functional impor- 

 tance than in the tj'pical forms of the European species. Fraas' figure of the lateral 

 ungual from Steinheim shows a phalanx which is again different from both the French 

 and American forms, though considerably nearer to the latter, as is shown by its 

 elongation and extended "basilar process." 



The phalanges of the median digit are likewise somewhat different from those of 

 A. aurelianense. Kowalevsky's account of their form in this species has already been 

 quoted in the description of Dssmatippus and it is unnecessary to repeat it here. The 

 dimensions of the proximal phalanx in A. equinum agree very well with the largest 

 specimens of the French species from Sansan, as given by Kowalevsky, except for the 

 greater antero-posterior depth of the proximal end. The groove for the carina of the 

 metacarpal is less profound and not continued so far forward ; the triangular rough- 

 ened surface for the attachment of the sesamoid ligaments is somewhat more pro- 

 longed towards the distal end. The intercondylar notch which emarginates the distal 

 trochlea on its palmar edge is much less conspicuous than in the European species 

 or the modern horse. 



The second phalanx is not preserved in the specimen. 



The ungual phalanx is unmistakably equine in character and yet very different 

 from the modern type. It also differs strongly from the visual form of ungual which 



