June 5, 1903.J 



SCIENCE. 



901 



is gigantic, or comparable to stich a form 

 as Macroeuphractus. 



2. Fully developed carapaces are found 

 in all of the armadillos and glyptodonts 

 of the period, but as yet no dermal ossifi- 

 cations have been found in connection with 

 any of the ground-sloths. This is the less 

 surprising, because very little is known 

 of the skeleton of the Santa Cruz My- 

 lodontidce, the only family in which these 

 ossifications could be expected to occur. 



3. The teeth are in all cases devoid of 

 enamel, rootless and tubular, though they 

 may be lobate, examples of which occur in 

 all three of the orders. No trace of a milk- 

 dentition has been observed. Premaxil- 

 lary teeth and the corresponding mandib- 

 ular teeth have been definitely found only 

 in the armadillos, though rudimentary 

 traces of such teeth are apparent in some 

 of the glyptodonts and they may also occur 

 in a few of the ground-sloths. 



4. The skull has few common features 

 throughout the series, each order having 

 its own characteristic type of structure. 

 The difference is largely in the relative 

 development of the cranial and facial re- 

 gions, which varies from the extremely 

 elongate skull, with long, slender rostrum, 

 of the armadillos, to the short, broad, deep 

 and almost cubical skull of the glypto- 

 donts. Sagittal and occipital crests are 

 never very strongly marked, but they are 

 present in most genera of all three orders, 

 and there is no such development of cranial 

 air-sinuses as took place at a later period. 

 In all of the known genera from this for- 

 mation, except Peltephilus, there is a more 

 or less prominent descending, suborbital 

 process given off from the zygomatic arch; 

 it may be formed by the jugal alone or by 

 the .jugal and maxillary, and in position it 

 may be at the anterior or the posterior end, 

 or in the middle of the arch. The arch 

 itself is always complete, never rudi- 



mentary, though in the Gravi'grada the 

 jugal is usually loosely attached, and has 

 been lost from most of the specimens. _ 



5. The neck has never more or less than 

 seven vertebrse, though in all of the arma- 

 dillos and glyptodonts the apparent num- 

 ber is much reduced by coossification. In 

 the same two groups the trunk is short and 

 the number of trunk-vertebrae small, and 

 in the glyptodonts these vertebrae are co- 

 ossified into long 'tubes,' one thoracic, the 

 other lumbo-sacral. In the Gravigrada, 

 on the contrary, the trunk is very long and 

 the trunk-vertebrffi numerous. In both 

 armadillos and ground-sloths the lumbar 

 and posterior thoracic vertebrse have very 

 complex accessory zygapophyses, which in 

 the former are as fully developed as at the 

 present time, but in the latter are some- 

 what less so than they became at a later 

 period. The sacrum may be long (Dasy- 

 poda, Glyptodontia) or short (Gravi- 

 grada), but always articulates with both 

 ilia and ischia. The tail is sometimes of 

 moderate length and sometimes very long, 

 but always heavy and always has a com- 

 plete series of chevron-bones. 



6. The limbs and feet differ greatly in 

 the three orders, and have comparatively 

 little in common. The scapula is broad 

 and has an extremely prominent spine and 

 acromion; the coracoid is very large in 

 the ground-sloths, reduced in the glypto- 

 donts and armadillos, except Peltephilus. 

 In all three orders the humerus has a simi- 

 lar general appearance, having small tu- 

 berosities, extremely prominent deltoid and 

 supinator ridges and internal epicondyle, 

 while the foramen is large. Ulna and 

 radius are separate and, except in the 

 ground-sloths, the former has a very large 

 olecranon. All the carpals are free, but 

 no genus has been found which has the 

 centrale. The manus is pentadactyl and 

 plantigrade,- though it is not improbable 



