Glyptodon , a gigantic fossil mammal, belonging to the edentate order with the megatherium and mylodon, but to the family dasy-pidoe or armadillos, found in the post-tertiary deposits of the pampas of South America, and especially in the neighborhood of Buenos Ayres. This animal, with the fossil genera above mentioned, establishes the transition between the sloths and the armadillos, and also indicates some pachyderm affinities. Four species have been described by Prof. Owen, of which the largest is the G. clavipes; this species, in the structure of the foot and the articulation of the lower jaw, approaches the pachyderms; it resembles the megatherioids in the strong descending process of the zygomatic arch, compressed from before backward; the cranium was protected by dermal plates, and its well developed ridges indicate the existence of very powerful muscles. The teeth, eight on each side of each jaw, have a large proportion of hard dentine, and are characterized by two lateral sculptured grooves, whose wide and dee]) channels divide the grinding surface into three portions; hence the generic name applied by Owen, which means "sculptured tooth.'" The back and sides were covered by a carapace composed of thick polygonal boriy plates, united by sutures, smooth on the inside, rough and sculptured externally, to the number of more than 2,000. The length of the largest living armadillo, covered with a flattencd shield, is about 3 ft.; the size of the glyptodon may be imagined from the measurement of its carapace in the museum of the royal college of surgeons: the length, following the curve of the back, is 5 ft. 7 in. - in a straight line, or the chord of the arc, 4f ft.; the breadth, following the curve, is 7 1/3 ft. - in a straight line, 3 1/6 ft.
The tail measured 1 1/2 ft. in length, and 14 in. in circumference at the circular base; it was slightly depressed toward the apex, and gently curved, with the concavity upward; the caudal vertebras were enclosed in an inflexible sheath of bony plates, terminated by two ossicles, like a bivalve shell, enabling it to pierce the soil if necessary. The feet were short and Stout, armed with depressed nails. The glyptodon, in its firm, convex carapace, scale-covered tail and head, short limbs, and consequent slow motions, presents many external analogies to chelonian reptiles, and in its size and shape must have resembled rather1 the living Galapagos tortoise than the great armadillo. Like the living armadillo, the extinct glyptodon was confined to the warm parts of South America. Other species described by Owen are G. ornatus, G. reticulatus, and G. tuberculatus, all obtained from the vicinity of Buenos Ayres.