362 E. S. Lull — Pleistocene Growid Sloth, 



than one third * the other two have only the portion adjacent 

 to the glenoid fossa preserved. The two more perfect speci- 

 mens, a right and a left, may constitute a pair, but this is 

 doubtful, as the less complete one is greater in its several com- 

 parable dimensions. Of the more perfect specimen, Cat. No. 

 10265, a right scapula, there is preserved the glenoid cavity 

 entire and most of the prescapular area, though none of its out- 

 line is present. The coracoid process is indicated and in its 

 present condition resembles in shape and size that of a young 

 Cholo&pus* It is probable, however, that were it preserved in 

 its entirety, it would be found to be connected with the 

 acromion by a bridge of bone arching over the proximal portion 

 of the prescapular fossa, as in Mylodon robustus. 



There is in the prescapular fossa the characteristic aperture 

 mentioned by Owen as representing the " supraspinal notch " 

 of other animals. In the Texan scapula this is not nearly cir- 

 cular as in M. robustus, but has the form of a narrow isosceles 

 triangle, the base of which is uppermost when viewed directly 

 from without. Viewed obliquely from the rear, the aperture 

 becomes subovate as it passes through the scapula obliquely 

 downward and forward. The spine begins about 30 mm above 

 the margin of the glenoid cavity and its inferior margin rises 

 in a decided curve to be lost through abrasion. 



The left scapula, however, shows what is evidently a com- 

 plete summit of the acromion process which rises in this, the 

 slightly larger animal, 40 mm above the level of the bone. The 

 appearance of the acromion itself, even though the missing 

 bridge were present, would be quite different from M. robustus, 

 but similar to the forms preserved in the Rancho La Brea.f 

 The prescapular fossa is roughened by irregular ridges of bone, 

 which, as in the case of the ilium, betray the enormous muscu- 

 lar development of the creature, and the same is true of the 

 inner face of the bone. The glenoid cavity is of marked 

 antero-posterior extent, while transversely the diameter is but 

 two-thirds the other extent, in decided contrast with the extent 

 of the humeral head. Two-thirds of the glenoid cavity lies 

 beneath the prescapular fossa which had approximately the 

 same area as the postscapular portion, if one may judge from 

 M. robustus and the Rancho La Brea skeleton. 



*In none of the three skeletons of Choloepus which I have before me is 

 the final union of the coracoid and acromion complete, although one (Cat. 

 No. 282) is that of a large animal with worn dentition and totally obliterated 

 cranial sutures. 



\ As shown by a photograph of the mounted skeleton in the Museum of 

 History, Science and Art at Los Angeles, presented through the courtesy of 

 Mr. Frank S. Daggett, director. 



