57 



section forming a long ellipse ; one side of the ellipse describes a 

 regular convexity ; the opposite side presents a median prominence, 

 with a depression on each side, corresponding with a median ridge 

 and two shallow channels which traverse the concave side of the tooth 

 longitudinally. The long transverse diameter, does not exceed in so 

 great a degree the short transverse diameter as in the tooth figured by 

 Cuvier, but the proportion of the length to the breadth and thickness 

 of the teeth compared cannot be determined, as both specimens are mu- 

 tilated. With respect to those differences which are determinable, they 

 are less than are presented by different teeth in the same jaw of the Me- 

 gatherium, of the Mylodon, and of the Scelidotherium ; and by no means 

 warrant the specific, much less the generic distinction of the Tenessee 

 Megalonyx from that discovered in the Cave in Green-briar County, 

 Virginia, and described by Cuvier. 



349. An anterior dorsal vertebra of a young Megalonyx : the epiphysial ends 



of the centrum are wanting. 



350. The fractured neural arch of a dorsal vertebra. The costal articular sur- 



face on the transverse process is a convex protuberance. 



351. A lumbar vertebra : there are two oblique or articular processes on each 



side of the anterior and on each side of the posterior part of the neural 

 arch, showing that the vertebrae in this region were interlocked, as in 

 the Megatherium and Mylodon, by a double tenon-and-mortice joint. 

 All the preceding vertebrae exhibit the wide canal for the spinal chord 

 which characterizes the Megatherioid animals generally. 



352. A cast in wax of the scapula of a young Megalonyx. It resembles that 



of the Mylodon in the equality of its height and breadth, and in the 

 almost equal partition of its outer surface by the spine. It has a large 

 perforation, instead of a notch, near the anterior part of the supra-spinal 

 fossa : if the termination of the fossa be over-arched in the Megalonyx, 

 as in other Megatherioid animals, by the conjoined acromion and co- 

 racoid, this characteristic structure has either disappeared from accidental 



i 



