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515. The tibia, in longitudinal section, of the Mylodon Darwinii: it is longer 

 in proportion to its breadth than in the Mylodon Harlani, the articular 

 cavity for the inner condyle of the femur has a wider oval figure ; the 

 outer margin of the shaft of the bone is thicker and more rounded than 

 in either the Myl. Harlani or Myl. robustus. The section shows the 

 absence of a medullary cavity, as in the tibia of the recent Sloths : a 

 close but rather coarse cancellous texture extends uninterruptedly from 

 the line of the proximal to that of the distal epiphysis : the compact 

 outer wall is two-thirds of an inch thick at the anterior part of the middle 

 of the shaft, and about half that thickness at the posterior part ; it 

 rapidly decreases in thickness from the middle towards the extremities of 

 the bone. 



Tribe Loricata. 



Genus Glyptodon. 



Those specimens of the present genus, which were presented to the College 

 by Sir Woodbine Parish, are from a low marshy place, about five feet below 

 the surface, in the bank of a rivulet, near the Rio Matanza, in the Partido of 

 Canuelas, about twenty miles to the south of the city of Buenos Ayres. 



516. A molar tooth, with the basal portion broken away, of the gigantic club- 

 footed Armadillo (Glyptodon clavipes, Owen). 



The whole length of the portion of tooth, which gives the generic 

 character of this extinct member of the loricate or Armadillo tribe, is 

 two inches and a quarter, and there is no indication of a diminution in 

 any of its diameters, from the grinding surface to the opposite fractured 

 end : in this respect the present tooth agrees with the form of the 

 sockets in the fragment of the jaw next to be described, which sockets 

 terminate abruptly without any contraction, and indicate by their depth 

 that the length of the present tooth, when entire, 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 



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