Nov.] AN EXISTING GROUND-SLOTH IN PATAGONIA 325 
which was believed to be quite extinct, a gravigrade edentate related 
to Mylodon and Pseudolestodon. 
The gravigrade edentates are reckoned among the oldest mammals 
which appeared upon the earth. The most ancient traces of them 
have been observed below the Guaranian Formation, with gigantic 
Dinosaurs, in the variegated sandstones of Patagonia, which are 
referred to the Lower Cretaceous. They become more numerous in 
the Pyrotherium beds of the Guaranian, develop gradually, and 
attain their greatest diversity during the Upper Eocene (Santa Cruz 
Formation). Thenceforward their variety decreases, but their size 
gradually increases, until in the Pampean they are represented by 
a certain number of gigantic forms, such as Megatheriwm, Lestodon, 
Mylodon, etc. Rare fragments in a bad state of preservation have 
been found even in the Post-Pampean deposits, but no one had 
supposed that they still had living representatives. 
Some of the Pampean genera show a very curious character : 
the body was protected on all sides by an incredible number of small 
irregular ossicles, which it is supposed were developed in the thick- 
ness of the skin, and thus became covered with a horny or scaly 
epidermis. The genera showing this peculiarity are Mylodon, Pseudo- 
lestodon, and Glossotherium. The other genera, such as Megatheriwm, 
Lestodon, and Scelidotherium, do not show any trace of it. Besides 
in the Pampean Formation these ossicles are met with in the Arau- 
canian Formation of Monte Hermoso and Catamarca, and also in the 
Entrerios Formation ; but no trace of them has been found in the 
Santacruzian, where the gravigrade edentates are so abundant, or in 
the earlier formations. We conclude from this that the character in 
question is not primitive, but acquired secondarily at a relatively 
modern period. 
These ossicles, comparable to large coffee berries, differ slightly 
in shape and size according to the genera. In Glossotheriwm they 
are large and flattened; in Mylodon they are smaller, irregular, 
elliptical, trapezoidal, or rhomboidal, with one side more convex or 
keeled, their diameter varying from one to two centimetres, though 
sometimes less. Their surface, more especially on the flattest side, 
shows some tiny depressions and perforations, and reticular tracery 
well seen under the magnifying glass. Their aspect is so character- 
istic that when one has once seen them they are recognised immedi- 
ately without any danger of being mistaken. 
Lately, several little ossicles have been brought to me from 
Southern Patagonia, and I have been asked to what animal they 
could belong. What was my surprise on seeing in my hand these 
ossicles in a fresh state, and, notwithstanding that, absolutely simi- 
lar to the fossil dermal ossicles of the genus Mylodon, except only 
that they are of smaller size, varying from 9 to 13 or 14 mm. 
