202 PROCEEDINGS OF THE ACADEMY OF [1893. 



DESCRIPTION OF A LOWER JAW OF TETRABELODON SHEPARDII 



Leidy. 



BY E. D. COPE. 



This species has been known hitherto by a third inferior molar 

 only. This has been described or figured at the following places of 

 reference : 



Mastodon shepardii Leidy, Proc. Acad. Philadelphia, 1870, p. 98; 

 1872, p. 472. Cope, American Naturalist, 1884, p. 524. 



Dibelodon shepardii Cope, Proc. Amer. Philosoph. Soc, 1884, p. 5, 

 partim. 



Mastodon observus Leidy, partim, Report U. S. Geological Survey 

 Terrs. I, p. 330, PI. XXI, 1873. 



A lower jaw of this species, lacking the condyles and supporting 

 the second and third true molars, was taken from the bluff in Crosby 

 County, Texas, from the same excavation that yielded the Pliau- 

 chenia sj)atula Cope, and within fifty feet of that at which the tooth 

 of the Dibelodon praecursor was obtained. It came into posses- 

 sion of Mr. M. M. Cox, of Estacado, from whom I obtained it by 

 purchase after my return from Texas. The acquisition of this 

 specimen is important as enabling me to determine the true charac- 

 ters of the species. Besides the last inferior molar, Leidy has 

 referred to it provisionally a fragment of a tusk, which, like the 

 molar, came from California. 



The second true molars are much worn, but they show, as was 

 to have been expected from the chai-acter of the third molar, only 

 three cross-crests without a rudimental fourth. The third true 

 molar exhibits exactly the simple characters of the typical specimen 

 described by Leidy ; that is, it has four well separated cross-crests, 

 and a very rudimental heel. The external half of each cross-crest 

 wears into a trefoil, while the internal half is simple and undivided, 

 and is a little anterior in position to the external half. The tooth 

 continues its width posteriorly, so that the transverse diameters at 

 the first and fourth cross-crests are equal. A marked character of 

 the species is the elevation of the anterior part of the ramus and the 

 decurvature of the symphysis, from which it results that the superior 

 face of the symphysis, or the spout, descends very steeply to its 

 extremity from the second true molar quite as in the proximal part 

 of the spout of Dinotherium. It has a very short horizontal por- 



