9O PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



In the lower jaw, T is extremely small ; the succeeding teeth increase in 

 size to ^, which is the largest of the series, and thence diminish to T ; the 

 lower teeth resemble the upper in form, but the principal grinding surface 

 is anterior. 



Skull (Plate XVI, figs. 1-5). In striking contrast to that of all other 

 known Santa Cruz armadillos, the skull is short, broad and heavy, with 

 very short and wide rostrum ; the occiput is rather low, the cranium long, 

 broad and quite capacious, its upper contour rising gently from the occip- 

 ital crest to the parietal eminence, which is not conspicuous and is placed 

 unusually far forward ; the profile descends steeply at the forehead and is 

 almost straight along the short rostrum ; the postorbital constriction is 

 shallow and there is no great expansion in front of it. The base of the 

 cranium is but slightly elevated and the occipital condyles project below 

 the level of the teeth. The occiput is broad, of subquadrate shape, nar- 

 rowing a little dorsally ; the crest is thick and rugose, but not very promi- 

 nent and the occipital surface is, for the most part, simply convex, without 

 marked elevations or depressions, except for a narrow groove near each 

 infero-lateral angle ; no paroccipital process is apparent ; the foramen 

 magnum is relatively small and transversely oval ; the condyles are small, 

 of more oval and less cylindrical shape than in any of the preceding 

 genera ; they are even more sessile and the articular surface is not invaded 

 by a sulcus from the outer side, as it is in all of the other contemporary 

 genera of armadillos. 



The basicranial axis is uncommonly long in proportion to the length of 

 the skull ; the basioccipital, which is long and broad, has a nearly plane 

 ventral surface, except posteriorly, where it is flared to form a prominent 

 lip for the foramen magnum ; the basisphenoid is of similar form, but 

 somewhat narrower. The tympanic differs from that of the other Santa 

 Cruz armadillos in forming a large, inflated and fully ossified bulla, which 

 is firmly connected with the surrounding bones and is relatively quite as 

 large as in Dasypus ; the external meatus is not so long as in the recent 

 genus and is a tube, the tympanic portion of which is incomplete, the 

 dorsal wall being formed by the zygomatic process and the anterior by the 

 postglenoid process, which is concave behind and very closely applied to 

 the tympanic. Owing to this intimate connection, to the very low origin 

 of the zygomatic process upon the side of the cranium and to the un- 

 usually anterior position of the opening, the meatus has the remarkable 



