42 



present molar has the same double curvature, and the same transverse 

 diameter as its presumed opponent, hut, owing to the flattening of its 

 fore-part, it has not the same antero-posterior diameter. 



From the province of Buenos Ayres. Purchased. 



229. A molar tooth of a tetragonal form, but with the anterior facet relatively 



broader and flatter than in the preceding, but narrower than in any of the 

 tetragonal teeth of the. upper jaw. It may be the second molar of the 

 lower jaw. 



From the Rio Salado. 



Presented by Sir TV. Parish, K.H. 



230. The third (?) molar of the lower jaw. This tetragonal tooth differs from 



those of the upper jaw, but most resembles the third in its slight and 

 single curvature. The anterior and posterior sides are convex, the outer 

 and inner ones are concave. 



From the Rio Salado. Presented by Sir TV. Parish, K,H. 



231. The fourth (?) molar of the lower jaw. It has a slight double curvature, 



and is tetragonal, like the preceding tooth, but the outer and inner sides 

 arc somewhat less concave. 



From the Rio Salado. Presented by Sir TV. Parish, K.H. 



232. A portion of the jaw of a Megatherium, containing the last molar tooth. 

 This is at least two-thirds smaller than the tooth which precedes it, and 

 thus corresponds with the last or fifth small molar of the upper jaw, 

 which is displayed in situ in Nos. 219 and 220. It differs from that 

 molar in being straighter, and in the smaller antero-posterior diameter 

 compared with the transverse diameter. The posterior surface is flatter, 

 and the angles dividing the four surfaces are more marked. Should this 

 be the last molar of the lower jaw, it will be the fifth molar, and the ad- 

 ditional number of the lower molar teeth will thus compensate for the 

 small size and simple form of the last molar in the Megatherium, as com- 

 pared with the other known Megatherioid genera. 



From the Rio Salado. Presented by Sir TV. Parish, K.H. 



