Mylodon harlani, from Rock Creek, Texas. 331 



the anterior one is imperfect. These teeth differ considerably 

 from each other in shape, and increase in size from the front, 

 the fourth and posterior tooth being double the size of the 

 first, and more compressed laterally ; it is also vertically con- 

 cave on its external aspect, and vertically convex on its inter- 

 nal aspect; the interior or mesial surface is strongly fluted, 

 and it has a deep longitudinal furrow on the dermal aspect, in 

 which respect it differs from the tooth of the M. laqueatus 

 previously described by me, of which the dermal aspect is 

 uniform, but to which, in all other respects, it has a close 

 resemblance. I suppose it therefore probable, that this last may 

 have belonged to the upper jaw. The three anterior molars 

 differ in shape and markings : they are vertically grooved, or 

 fluted, on their interior and posterior aspects, a transverse sec- 

 tion presenting an irregular cube. The length of the crown of 

 the posterior molar is two inches : the breadth about live-tenths 

 of an inch : the length of the tooth is three inches and six- 

 tenths. The diameter of the penultimate molar is eight-tenths 

 by seven-tenths of an inch. The length of this fragment of 

 the jawbone is eight inches and four-tenths ; the height three 

 inches and six-tenths : the length of the space occupied by the 

 alveolar sockets five inches and eight-tenths. The crown of 

 the tooth presents no protuberances, but resembles that of the 

 Sloth ; the roots are hollow.' "* 



This fossil, as stated above, was referred by Doctor Harlan 

 to his Megalonyx laqueatus. Owen secured from M. Laurillard 

 of the Jardin des Plantes, Paris, a drawing of a cast of the 

 type jaw which the Museum possessed. Basing his conclusion 

 upon this drawing, Owen says further : 



" I am disposed to regard the amount of difference recogniz- 

 able in every tooth in the lower jaw in question (figs. 3 and 4) 

 as compared with the molar tooth either of Megalonyx Jeffer- 

 sonii (fig. 1) or Megalonyx laqueatus (fig. 2) to be such as to 

 justify its generic separation from Megalonyx on the same 

 grounds as Megalonyx is distinguished from Megatherium, and 

 for the subgenus of Megatherioid Edentata, thus indicated, I 

 would propose the name of Mylodon. The species of which 

 the fossil remains are described by Dr. Harlan may be 

 dedicated to that indefatigable Naturalist who has contributed 

 to natural science so much valuable information respecting the 

 Zoology, both recent and fossil, of the North American con- 

 tinent." 



Leidy in 1855 f redescribes and figures the type specimens 

 of Mylodon harlani, after which he enumerates other material 



* Harlan, Medical and Physical Besearches, p. 334, 1835. 

 •f Leidy, J., Smithson. Contrib. Knowl., vol. vii, art. V, pp. 47-49, 58, pi. 

 14, figs. 1-3, pi. 16, figs. 19-20. 



