MEOATHERIUM (properly Megalotherium)  , a huge extinct edentate mammal from the Pleistocene deposits of Buenos Aires, typifying the family Megatheriidae (or Megalotheriidae), and by far the largest representative of the Edentata . Except, indeed, for its relatively shorter limbs Megatherium americanum rivalled an elephant in bulk, the total length of the skeleton being 18 feet, five of which are taken up by the tail . The Megatheriidae, which include a number of genera, are collectively In form, as shown in fig . 2, the teeth are quadrangular prisms, each of which is surmounted by a pair of transverse ridges . They grew apparently throughout life, and were implanted to a great depth in the jaws, being 7 or 8 in: in length, with a cross-section of at least an inch and a half . The ridges on the crown are due to the arrangement of the vertical layers of hard dentine (fig . 3, (I), softer vasodentine (v) and cement (c) . The skull is relatively small, with the lower jaw very deep in its central portion, and produced in part into a long snout-like symphysis for the reception, doubtless, of a large and fleshy tongue (fig . 2) . Unlike sloths, the megatherium has seven cervical vertebrae; and the spines of all the trunk-vertebrae incline backwards . The pelvis and hind-limbs are much more powerful than the fore-quarters; thereby enabling these animals, in all probability, to rear themselves on their hind-quarters, and thus pull down the branches of trees: if not, indeed, in some cases to bodily uproot the trees them-selves . Large chevron-bones are suspended to the vertebrae of the- tail, which was massive, and probably afforded a support when the monster was sitting up .

The humerus has no foramen, and the This school was I.—Skeleton of the Megatherium, from the specimen in the Museum of the Royal

College of Surgeons of England . known as ground-sloths, and occupy a position intermediate between the sloths and the ant-eater: their skulls being of the type of the former, while their limbs and vertebrae conform in structure to those of the latter . As in the other typical South American edentates, there are no teeth in the front of the jaws, while those of the cheek-series usually comprise five pairs,in the upper and four in the lower . In nearly all the other Pleistocene forms these teeth were subcylindrical in shape, with the summit of the crown (except sometimes in the first pair) forming a cup-like depression; enamel being in all cases absent . From all these Megatherium differs in the form and structure of the teeth . (From Owen.) whole fore-limb was very mobile . The first front toe was rudimentary, having no phalanges, but the fifth was rather less aborted, al-though clawless; the other three carried enormous claws, protected by reflected sheaths . The hind-foot is remarkable for the great back-ward projection of the calcaneum, and likewise for the peculiar shape of the astragalus; the middle toe alone carries a claw, this being of huge size, and ensheathed like those of the fore foot . No trace (From Owen.) of a bony armour in the skin has been detected; but, from the evidence of other genera, it may be assumed that the body was clothed in a coat of long, coarse hair . Although similar teeth occur in the phosphorite beds of South Carolina, which may have been transported from elsewhere, no undoubted remains of Megatherium are known from North America . The typical species ranged from Argentina and Chili to Brazil. for certain small ground-sloths from Patagonia with Megatheriumlike teeth, see MYLODON . (R .