518 Geological Society. 



surfaces two deep grooves, each extending from the opposite sides 

 about one third of the transverse diameter of the tooth and through 

 its whole length, dividing the grinding surface into three portions, 

 joined together by the contracted isthmus interposed between the 

 opposite grooves. The teeth thus exhibit a more complicated form 

 than those of any known Edentate, and seem to indicate a transition 

 from that family to the Pachy dermal Toxodon. 



The fragment of the jaw discovered at Villanueva consists of a 

 portion near the extremity of the left ramus, and includes three 

 alveoli, which slightly increase in size as they are placed further 

 back. 



The humerus, of which the distal half has been received, agrees 

 most nearly with that portion of the humerus of the Dasypus, but 

 the internal condyle is not perforated ; the depressions also above the 

 trochlea, both in front and behind, are relatively deeper, and in the 

 side opposite the deltoid trochanter there is a rugged raised surface 

 for a muscular insertion, of which Mr. Owen has not perceived any- 

 thing analogous in the Armadillos. From the humerus of tlie Me- 

 gatherium it differs in not presenting the extraordinary expansion of 

 the distal extremity exhibited in that animal ; but the internal con- 

 dyle in the Megatherium is also imperforate. 



The radius of the Glyptodon corresponds very nearly with that 

 of the Armadillo, but it differs from the radius of the Megathere in 

 being three times less in every dimension, and by well-marked dif- 

 ferences in all the details of structure. 



The ungueal phalanges of the Glyptodon approach most nearly 

 those of the species of Dasypus ; but in their shortness, as compared 

 with their breadth and depth, they resemble still more the ungueal 

 phalanges of the Pachyderms. Mr. Owen is of opinion that they 

 were encased in strong, short, hoof-like claws ; and that they exhibit 

 rather the base of an anterior column of support to an animal clad 

 in a ponderous cuirass than instruments especially designed for 

 scratching or digging. There cannot be a greater contrast than is 

 presented between the short, broad, and flat phalange of the Glyp- 

 todon, and the long and compressed claw-bone of the Megatherium. 



Of the posterior extremity of the Glyptodon, the tibia, which is 

 anchylosed to the fibula, presents the structure characteristic of the 

 tibia of the Armadillos ; while in the Megathere the corresponding 

 bones deviate widely in their proportions, and in the conformation of 

 the distal articular surface from those of the Glyptodon. The con- 

 formation of the astragalus, calcaneum, the cuboid, scaphoid, and 

 internal cuneiform bones, also of the metatarsals of the three middle 

 and largest toes, the three phalanges of the second and middle, and 

 the distal phalanges of the third and fourth toes, were described in 

 great minuteness, but it is not possible to abridge the details. 



Mr. Owen, however, stated that when the bones of the hinder ex- 

 tremity are arranged in their natural juxta-position, they present a 

 foot of such singular proportions as to be without a parallel in the 

 animal kingdom. The nearest approach to its broad, thick, short, and 

 massive proportions is made by the skeleton of the fossorial extremity 



