Mr. Owen on the Glyptodon clavipes. 87 



entire tooth was about four inches ; the antero-posterior diameter of the tooth is 

 one inch ; the transverse diameter varies from six to seven lines. The three 

 sockets in the fragment of the jaw give the same general proportions, though they 

 vary a little as to size, whence it is shown that the teeth of the Glyptodon are 

 much more compressed than those of the Megatherium ; they differ still more 

 materially in their intimate structure, which corresponds with that of the Arma- 

 dillos: the main body of the tooth, or the dentine, consists of fine calcigerous tubuli, 

 radiating with a pretty straight course from the medullary cavity ; the dentine is sur- 

 rounded by a very thin layer of csementum, and the pulp-cavity, at the upper part 

 of the tooth, is consolidated by the ossified remains of the pulp, which is harder than 

 the surrounding dentine. The teeth of the Glyptodon, however, differ in a marked 

 degree from those of all the known species of Armadillo, in being traversed, through 

 the whole length of both their outer and inner sides, by two broad and deep angular 

 grooves, each extending from the opposite sides about one-third of the transverse 

 diameter of the tooth, so as to divide the grinding surface into three portions, joined 

 together by the contracted isthmus interposed between the opposite grooves. Of 

 these portions the posterior one is broader than the other two. The sockets pre- 

 sent longitudinal angular ridges, corresponding to these channels or flutings, and 

 prove that they were continued through the whole length of the tooth ; this is slightly 

 curved^ and the concavity is turned inwards in the teeth of the lower jaw, as in the 

 Toxodon. I have elsewhere observed that the teeth of the Glyptodon exhibit a more 

 complicated form than those of any recent or extinct edentate species hitherto dis- 

 covered, and seem to indicate a transition from the Edentata to the pachyder- 

 matous Toxodon : it will be hereafter seen that the modifications of the locomotive 

 extremities bespeak a similar tendency in the Glyptodon to the multungulate 

 Pachyderms. 



The fragment of the jaw of the Glyptodon, discovered at Villanueva with the 

 other bones now about to be described, consists of a portion broken off from near 

 the extremity of the left ramus, and includes three alveoli, which slightly increase 

 in size as they are placed farther back ; this circumstance, as well as the anterior 

 position of the sockets, correspond with the sketch of the entire Glyptodon, already 

 published by Sir W. Parish, and make us regard with more confidence the indi- 

 cations of an affinity to the Megatherium in the double flexure of the lower jaw, and 

 the long descending process from the zygoma represented in that sketch. As the 

 general correspondence of the conformation of the alveoli with the structure of the 

 teeth has already been noticed, it is only necessary to subjoin their dimensions. 

 The antero-posterior diameter of the first is ten lines ; the transverse diameter of 

 its posterior division, which corresponds to the broadest part of the tooth, is five 

 lines ; the antero-posterior diameter of the second socket twelve lines ; its trans- 

 verse diameter six lines and a half ; the antero-posterior diameter of the third 



