108 
PEOFESSOE OWEX OX THE SCELEDOTHEEE. 
in number, all of one kind, arranged according to the Megatherioid formula: \iz. 
wi, They are simple, long, fangless, and of the same thickness from the 
implanted to the exposed end ; the former is excavated by a deep conical cavity, the 
latter worn into a shallow depression, and somewhat obliquely, reaching to the level of the 
inner alveolar wall in the upper jaw, and to the outer one in the lower jaw. 
In the upper jaw the shape of the anterior tooth (Plate IX. i) is shghtly modified 
in two of the skulls of the Scelidothere from Buenos Ayres in the British Museum. 
In one, its transverse section more resembles that of the same tooth figured in the frag- 
ment described in my original memoir on the genus *, the straightest and broadest side 
being the inner one : in the other skull the outer side shows those proportions ; the 
teeth being naturally implanted in both skulls : the general form of this section is an 
irregular oval, II lines in long diameter ; the length of the tooth is 2^ inches ; it is very 
slightly curved, with the convexity dhected forwards and inw^ards. 
The other four teeth gradually diminish in size, and are more or less three-sided with 
the angles rounded off, in transverse section ; the longest side being turned outwards 
and backwards, and bemg slightly concave : the opposite angle is more developed in one 
than in the other skull, in the second and third molars : these are more nearly equal in 
size than the last two molars. The longest diameter of the grinding surface of the 
penultimate molar is 9 lines, that of the last molar 7^ lines. The longitudinal extent of 
the dental series in both adult skulls is 4 inches 4 lines. The length of the last tooth is 
2f inches ; that of each of the three middle teeth is 3 inches. 
In the lower jaw (Plate IX. fig. 2) the first molar (^) is broader than the second and 
third : its transverse section is triangular with the angles rounded off, the longest side 
turned inwards. The second (ii) and third (Hi) teeth are of equal size and similar shape, 
the transverse section being triangular with the apex thick and obtuse ; the base is much 
shorter than the sides, is slightly indented, and turned outwards and a httle foi-wards ; 
the rounded apex in the opposite direction ; the anterior side is more concave than the 
opposite side. The last molar (iv) is the largest and most complex, its grindhig surface 
consisting of two lobes produced by two opposite unequal-sided channels traversing the 
tooth longitudinally : the lobes are subequal, and placed obliquely one before the other. 
The teeth consist of a central axis of vaso-dentine, a wall between I hne and 2 lines 
thick of hard dentine, and a very thin outer coat of cement. 
Comjyarison of the Skull and Dentition. 
In the comparative simplicity of the malar bone and of the grinding siuface of the 
teeth, in their close and regular arrangement and in the narrowness of the palate, in the 
incomplete orbit and the uninterrupted or more simple outline of the under jaw, the 
Scelidothere manifests its nearer affinity to the Mylodon than to the Megathere ; but 
in many respects it is an intermediate form, as is shown by the long premaxillaries and 
the corresponding length and slenderness of the symphysis of the lower jaw. The occi- 
* Op. cit. PL XXIII. fig. 3, 1 . 
