III.] GROUND-SLOTHS. IO3 



limb-bones and vertebrae like those of the anteaters. The skull is, 

 however, somewhat more elongate than in the former, and in the 

 case of the genus Scelidotherium approximates to that of the latter. 

 The Plistocene forms include by far the largest representatives of 

 the order, the Megalotherium 1 attaining a total length of about 

 eighteen feet, with a bodily bulk fully as great as that of an 

 elephant. Whereas all the members of the family whose remains 

 occur in the Plistocene walked on the outer sides of their feet, in 

 the small ancestral Patagonian forms this specialised character 

 seems to have been less developed. 



The typical genus Megalotherium which includes several 

 species, ranging in time from the Monte Hermoso and Cordoba 

 beds to the Pampean, and in space from Argentina and Chili to 

 South Carolina and Texas is sufficiently distinguished by having 

 the teeth in the form of large quadrangular prisms, sometimes 

 measuring as much as a foot in length, and wearing on their sum- 

 mits into a pair of transverse ridges, owing to the presence of layers 

 of unequal hardness. The allied genus Mylodon, including smaller 

 forms which may be compared in size to rhinoceroses, differs from 

 the preceding in the structure of the teeth, which are similar to 

 those of the sloths ; the skull, as shown in the figure on 

 p. 104, being comparatively short, with the teeth extending nearly 

 up to the extremities of the jaws. In the skeleton of this genus 

 the limbs are of moderate length and very powerful. The two 

 outer toes of the fore feet are rudimental and clawless, but the 

 three innermost provided with claws, of which the third is much 

 larger than either of the others, this discrepancy being carried 

 to a still greater extent in Megalotherium. It will be observed 

 that the creature walked on the outer sides and part of the upper 

 surfaces of the fore feet after the manner of a sloth ; but, unlike 

 the latter, only the outer sides of the hind feet were applied to the 

 ground ; the great middle toe, which in Megalotherium carried a 

 gigantic claw, not touching the ground at all. In the structure of 

 their feet these animals are thus more like anteaters than sloths, 

 although the hinder pair are of a somewhat more specialised 

 structure than in the latter. It may be mentioned that the 



1 The name Megatherium clearly requires amendment to Megalotherium. 



