322 



ON THE EXTINCT MAMMALIA OF 



supposed to beloug to the same animal. The length of the crown at the middle 

 externally is about an inch ; the breadth of the triturating surface eleven and a 

 half lines ; its thickness seven lines. 



20. A half-dozen isolated molars, of various ages, and positions intermediate in the 

 permanent series. They are represented in figures 30 — 36, and, with the last de- 

 scribed specimen, are of larger proportions than any of the others, being about the size 

 of those of the Ass. They probably belong to one or more species of Hipparion. 



21. Four tem2Dorary molars, represented in figures 37, 38, 41. The two repre- 

 sented in the last figure are contained together in a fragment of the lower jaw, and 

 appear to be the second and third of the left side. 



22. An inferior molar, probably a second or third of the permanent series, repre- 

 sented in figure 40. 



23. A series of bones together composing a complete fore foot, about the size of 

 that of the Ass, in the Niobrara collection. The median metacarpal and succeed- 

 ing two phalanges have every appearance of having belonged to the same indi- 

 vidual ; and the cofiin bone, though probably from a different skeleton, accords in its 

 proportions with the preceding bones. 



The median metacarpal bone is roughened, at the sides posteriorly, the entire length 

 of the shaft, as if for. the conjunction of lateral metacarpals, as has been recognized to 

 be the case in the genus Hipparion, to which these fossils also probably belong. The 

 measurements of the metacarpal are as follow: 



Length in the axis of the bone, . 



Width of the carpal articular surface. 



Diameter of the same from before backwai-d, 



Breadth of the shaft at the middle, 



Circumference of the same. 



Breadth of the phalangial articulation, . 



The measurements of the pastern bone are as follow : 



Length in the axis, .... 

 Breadth of the proximal end, 

 Breadth of the shaft at middle, 

 Breadth of the distal articular surface, 



The measurements of the coronary bone are as follow 



Inch. Lia. 



8 6 

 18 

 13 

 14 

 41 

 18 



Lines. 



. 27 



. 19 



. 13 



. 17 



