408 ZOOLOGY. 



of the tatous by their structure ; but the two deep grooves which are seen 

 on their interior surface seem also to indicate a sort of passage to the 

 pachyderms through the genus Toxodon. The cuirass is composed of 

 apparently hexagonal plates, united together by serrated sutures. A single 

 species is known, G. clavipes, which reached a very large size ; it inhabited 

 the JDampas of Buenos Ayres during the pliocene period. 



The genus Hoplophorus has also the descending apophysis of the zygo- 

 matic arch and the heavy forms of Megatheridse. But the feet are shortened 

 as in Glyptodon, and the molars recall to mind those of some rodents. It 

 was secured with a cuirass composed of hexagonal plates. Several species 

 are found in the Brazilian caverns, two of which. H. euphractus and H. sel- 

 lowii, reached the bulk of an ox. 



The genus Pachytherium is known only by a few bones of the extremities, 

 which indicate still heavier forms. A single species is known, P. magnum, 

 from the caverns of Brazil. 



The genus Chlamidotherium comes very near the tatous. It has the 

 osteology and the cuirass of the encouberts, and the fore feet of the cachi- 

 cames. There are small incisors analogous to those of the encouberts, 

 and molars which call to mind by their forms those of the sloths and Mega- 

 theridee. Two species were discovered in the caverns of Brazil, Cli. hum- 

 holdtil, of the size of the tapir, and Ch. gigas, equalling the largest rhino, 

 ceros. 



The genus Euryodon is characterized by the molars transversely com- 

 pressed. As yet only a single species, of the size of a small hog, is known. 

 From Brazil. 



In the genus Heterodon the teeth are more unequal in form as well as in 

 size. The first and the last ones are like thin cylinders. The anterior is 

 oval in transverse section, while in the posterior it is cordiform. The only 

 species known was of the size of a rabbit. From Brazil. 



Group 3. Tardigrada. 



The group of Tardigrada, characterized by a short face, is composed of 

 two families, one of them hitherto known only in a fossil state, the Mega- 

 theridcB, the other only as recent, the Tardigrada proper, or Bradipodidae, 

 or Gravigrada. 



Fam. 1. Megatherid^, whose history belongs to the ancient world, 

 resemble Tardigrada proper in having teeth in the shape of hollow cylinders, 

 composed only of ivory and cement, without enamel. The ivory forms a 

 tube filled by a more porous substance. The shape of the head is also very 

 similar ; it is short, as if truncated, and the zygomatic bone forms a great 

 descending apophysis, a character found nowhere else in the class of mam- 

 malia. The skeletons are very much alike, particularly in the structure of 

 the shoulder, where the acromion and coracoid bones are soldered together. 

 But in the other peculiarities of their structure they come nearer the other 

 families of Edentata. Their general form was bulky, theii body heavy, 

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