OWEN ON THE GLYrTOBON. 261 



series of caudal vertebrae inclosed in an inflexible sheath composed 

 of closely united dermal ossicles of various forms and sizes, but 

 disposed in a regular and beautiful pattern. The osseous substance 

 of the sheath increases in thickness from half an inch near its 

 base to one inch and three quarters near its obtuse apex. The 

 dermal ossicles are united to the internal skeleton of the tail, and 

 defended from outward pressure by processes which radiate from 

 the bodies of the caudal vertebrae. The dermal armour consists 

 of central, large, or principal ossicles, and peripheral, small, or 

 accessory pieces, the latter occupying the interspaces of most of 

 the larger ossicles in a single series. The larger ossicles differ in 

 size, increasing as they approach the end of the tail, and with 

 great regularity, where they form the two lateral series, which 

 terminate by a pair of large, sub-elliptic, thick, hollow ossicles, 

 which inclose the end of the tail like a bivalve shell, defending 

 this part when dragged along the earth and even enabling it to 

 pierce the soil like an implement sheathed with iron. The number 

 of the lateral plates on each side of the considerable portion of the 

 tail preserved is nine ; from the first of these to the fourth the 

 number of intermediate principal ossicles below each pair of 

 lateral plates is six of nearly equal size ; beyond this they decrease 

 to four and three in number. At the superior interspace of the 

 two lateral series there are six sub-equal principal ossicles between 

 each pair of lateral plates as far as the fourth ; they then decrease 

 to five and four in number, those at the centre being of smallest 

 size. 



The circumference of the base of the tail is fourteen inches, that 

 of the apex at the interspace of the penultimate and last lateral 

 plates ten inches. The length of the last lateral plate is three 

 inches and a half, its breadth is three inches. 



An anterior caudal vertebra is another interesting fossil with 

 reference to this part. The specimen exhibits part of the anterior 

 border of the verticillate bony dermal covering or sheath of the 

 tail. This covering was attached to the vertebra by a close syn- 

 desmosis connecting the extremities of the processes which radiated, 

 like the spokes of a wheel, from the centrum or body ; the muscular 

 and ligamentous tissues, Avhich occupied the interspaces now filled 

 by the matrix or soil formation in which the fossil was imbedded, 

 would also form a medium of attachment between the endo- and 

 exo-skeletons of the tail. The length of the body of this vertebra 

 is two inches and a half : the diameter of the articular surface of 

 the body is one inch and a half. 



2. Glyptodon ornatus, Owen. . 



This species is indicated by a portion of a carapace, including 

 four or five dermal ossicles of a smaller species of Glyptodon than 

 the one already described. The outer surface of the ossicles is 

 relatively smoother, and the central disc smaller as compared with 



s 3 



