Mr. Owen on the Glyptodon davipes. 98 



parison between it and the corresponding bone of the Glyptodon. It measures 

 twenty-eight inches in length, and six inches and a half across its distal end. 



Besides the disparity of size, which is most striking — the radius of the larger 

 Edental being more than three times greater in every dimension, — we find well- 

 marked differences in all the details of its conformation : its proximal articular 

 surface is subcircular and uniformly concave ; the margins of this concavity are 

 not extended in any direction, so as to overhang any part of the shaft of the bone ; 

 this shaft is compressed, and the radial edge produced ; the concave distal arti- 

 cular surface is nearly at right angles with the axis of the bone, and there is no pro- 

 cess developed from its anterior part. The Megatherium, in deviating from the 

 Glyptodon in all these points, deviates of course in the same degree from the Arma- 

 dillo-tribe. 



To judge from the figure which Professor D'Alton has given of the ulna of 

 Sellow's Glyptodon, this bone equally illustrates the affinity of the latter animal to 

 the Dasypodoid, and its deviation from the Megatherioid families of Edentata. 



Two unguial phalanges, which, from their obliquity, had been referred by Mr. 

 Clift to the fore-foot, are proved to be correctly so referred by the memoir of Pro- 

 fessor D'Alton, in which the bones of nearly the entire fore-foot are excellently 

 described and figured. The difference in size between the bones so figured and the 

 present phalanges corresponds exactly with that which has been noticed in the 

 radius of the two specimens ; the smaller phalanx in the present collection belongs 

 to the third, the larger to the fourth toe, of the left fore-foot. In both, the proxi- 

 mal extremity offers a double shallow articular pulley ; it is placed obliquely, so 

 that the end of the bone must have been inclined somewhat downwards. The 

 upper and outer margin is produced ; the bone is thicker on the inner than the 

 outer side, towards which it slightly bends ; the upper surface is evenly convex, 

 but pitted with numerous vascular impressions, which are strongest at the margin ; 

 the under surface of the phalanx presents a rough, convex protuberance, occupying 

 the posterior half of the under surface. 



Of all Edentata, existing or extinct, the species of the genus Dasypus are those 

 to which the Glyptodon makes the nearest approach in the structure of the un- 

 guial phalanges ; but in their shortness, as compared with their breadth and depth, 

 these bones of the Glyptodon resemble still more the unguial phalanges of the 

 Pachyderms : the middle and proximal phalanges of the fore-foot of the Glyptodon, 

 which are described and figured in the memoir of Prof. D'Alton, differ from those 

 of both the Armadillos and the Pachyderms in their very remarkable shortness, 

 and in the flatness of their articular surfaces. The short, broad, depressed terminal 

 phalanges of the Glyptodon must have been encased in correspondingly short and 

 strong hoof-like claws, and have presented a striking contrast with the foot of the 



VOL. VI. SECOND SERIES. N 



