387 



orbits, are most rugose and indicate a more intimate adhesion to the super- 

 incumbent osseous dermal helmet. The lacrymal foramen r is pierced imme- 

 diately in front of the anterior border of the orbit. 



The difference in the development of the temporal muscles manifested by the 

 Glyptodon and Mylodon, in the position of the ridges on the fossil cranium, in- 

 dicates a corresponding difference in the power of mastication and in the density 

 of the alimentary substances habitually selected by each species : the greater 

 proportion of hard dentine in the teeth of the Glyptodon, and the greater num- 

 ber of the teeth, which appears to have been thirty-two, eight on each side of both 

 jaws, coincide with the characters of the cranium and support the inferences 

 thence deducible. 



PLATE IV. 



Portions of the bony armour of the different Glyptodons or extinct Gigantic 

 Armadillos : natural size. 



Fig. 1. A view of the outer surface of three ossicles taken from the anterior 

 border of the carapace of the Glyptodon clavipes. 



a, The median eminence, the large size of which characterizes the ossicles 



forming the border of the carapace, and is accompanied by a diminution of 



b, The peripheral portion of the ossicle, which, at the same time, loses the 



marks of its subdivision into smaller eminences. 



c, The median eminence of an anterior marginal ossicle, which, at this part, 



extends outwards and forwards in the form of a transversely, oblong, ob- 

 tuse-angled prominence ; the marginal part of the ossicle being almost 

 obliterated. 



d, The sutural margin of the ossicle. 



Fig. 2. A view of the internal surface of the same ossicles : d, the suture. 



Fig. 3. A side view of a hexagonal ossicle from the middle of the upper 

 surface of the carapace of the Glyptodon clavipes ; showing the thick- 

 ness of the bony armour at that part, and the roughness of the sutural 

 surfaces. 



Fig. 4. The external surface of an ossicle from the side of the carapace, 

 showing a variety arising from an accessory peripheral tubercle, which 



3 D 2 



