m the Museum of Buenos Ayres. 91 



pared with that of the teeth of the Carpincho : it is peculiar to 

 the Glyptodon, because no other aniDial equally large posaesses 

 teeth of this form. The zygomatic arch of this animal, besides 

 being thick, was provided with a perpendicular prolongation 

 which descended from underneath the eye, giving us a proof 

 that it ground hard substances. This prolongation is only dis- 

 covered in antediluvian animals, such as the Megatherium, Mylo- 

 don, or the Scelidotherium *. 



As we only intend to describe the principal parts, I shall here 

 conclude the cranium, and shall give a description of the differ- 

 ences in the teeth of the various species of the animal, they being 

 the only parts which can be compared one with another. 



I have in my possession portions of three lower mandibles, 

 two of which belong to G. clavipes, and the other (which is com- 

 plete) to G. spinicaudus. The general form and the relations of 

 the teeth are the same ; but the form of the prisms in each tooth 

 is a very little different. The sides of each rhombic prism of 

 G. clavipes are a little curved into the interior of the prism ; but 

 those of G. spinicaudus have a slight external elevation ; and for 

 this reason the dental prisms in the former species appear to be 

 thinner and more acute at the comers, and those of the second 

 thicker and more obtuse. In the work of Dr. Lund (second 

 part, tab. 35. f. 2, 3 &4) there are figures of two teeth which 

 appear to exhibit a slight difference, as regards the form of the 

 prisms, from those of my two species, demonstrating that then 

 was a slight difference between the Brazilian species and thoM 

 of Buenos Ayres. These teeth are from the upper jaw, — fig. 2 

 being the first, and fig. 3 the last tooth on the left side. 



The neck of the Glyptodon comprises seven vertebrae, as in 

 other Mammalia ; but only the first and the last are moveable, 

 the other five being united into one solid mass ; hence it results 

 that the neck is very short and powerful. The first, or atlas, is of 

 considerable size, and of the form occurring in other Mammalia; 

 its two wings are laterally compressed^ ascend posteriorly, and 

 have three smooth and even slightly concave excavations for their 

 articulation with the second vertebra. This (the axis) is short 

 and united with the four following ones in one piece, which de- 

 velopes in front a small tuberosity for its articulation with the 

 atlas. At each side of this bone there is a strong prolongation 

 inclined backwards, and before it four foramina for the trans- 

 mission of nerves, which indicate the five united vertebrae. 

 There is another prolongation on the top of the arch above the 

 vertebral column, which is also inclined backwards, and is ter- 

 niinated by three points. This particular bone is already known 



* [It i> also visible in the existing Sloth. — Transl.] 



