74 



tebrse ; nothing analogous to which exists in the Mylodon, nor indeed in any 

 other Edentate animal. The posterior part of the spinal ridge rises to an inor- 

 dinate height in the Chlamyphore, and expands at its summit into a triangular 

 plate, concave at its upper surface, and anchylosed by the sides of its base to two 

 broad and thin osseous plates rising almost vertically from the upper part of the 

 tuberosities of the ischia ; by this structure two large pelvic foramina are formed 

 in addition to the thyroid and ischiadic ones common to other Edentata, and 

 neither the Mylodon nor Megatherium offer any approach in their pelvic organi- 

 zation to the above-described peculiarities in the Chlamyphorus. The two hinder 

 buttress-like tuberosities which prop up the posterior part of the carapace are 

 equally pecuUar to the Chlamyphore. 



It is to the Sloths therefore that the Mylodon most nearly approaches in its 

 pelvic structure, and all the points in which it differs are instances of its closer 

 resemblance to the Megatherium. The more developed and continuous spines 

 of the sacrum, the more expanded ilia, their broad and flattened labrum, are 

 points in which the Mylodon and Megatherium alike differ from the Sloths. In 

 some points of its pelvic organization the Megatherium nevertheless differs in 

 a marked degree from the Mylodon. It has only five true sacral vertebrae, and 

 this consolidated segment of the spinal column is not augmented at the expense 

 of the lumbar vertebrae*, which are distinct in both the Madrid specimen and 

 in that in the Museum of the College of Surgeons. The transverse processes of 

 the two last sacral vertebra3 are relatively thicker and stronger than in the My- 

 lodon ; the spine of the fifth sacral vertebra is not confluent, at least at its base, 

 with the thick and strong crest formed by the conjoined four anterior spines. 

 The free margin of this crest, which is broken ofi" in the specimen in the Col- 

 lege Museum, would seem, from the figures of the Madrid spe'cimen, to be di- 

 vided, indicating that the continuous ossification had not attained, as in the 

 Mylodon, the summits of the spinous processes. The broad arched labrum of 

 the iha gives the thickness of the bone at that part, and is not formed by a bending 

 forward of the plate itself, as in the Mylodon. The ischium has a greater relative 

 breadth, and the symphysis pubis a greater relative antero-posterior extent in the 



* The anchylosed bodies of the three lumbar vertebrae of a second individual of the Mylodon robustus 

 were transmitted mth the entire skeleton described in this memoir to the College of Surgeons, thereby- 

 indicating it to be a specific structure, and not accidental to one particularly aged individual. 



