7O PATAGONIAN EXPEDITIONS! PALEONTOLOGY. 



Dentition. --The dental formula is 7 -~, and there are no premaxillary 

 teeth. In form the teeth resemble those of the modern Zaedyus, but are 

 both relatively and actually smaller; the anterior teeth, especially T , ^ and 

 , are very small and much compressed, but posteriorly the teeth increase 

 in size ; they are of compressed oval section, with the long axis of the 

 ellipse directed antero-posteriorly ; the grinding surface of most of the teeth 

 is bevelled to a transverse edge, as in Dasypus, and displays two kinds 

 of dentine, a denser layer on the periphery, which in the fossils is of a 

 lighter color, and the softer, darker vaso-dentine, which forms most of the 

 teeth and is often worn into a concave surface ; in the center is a small 

 spot of different appearance. 



Skull (Plate VI, figs. 1-4, 15-17). --In general appearance, the skull 

 is not unlike that of the recent Zaedyus, but is decidedly more slender 

 and elongate ; the cranium is narrower and less capacious and the post- 

 orbital constriction deeper and more abrupt ; the rostrum is longer and 

 more slender and tubular and the face narrows more suddenly in front of 

 the orbits ; the forehead is narrower and the frontal sinuses but moderately 

 developed. Thus, the face is much shallower vertically and, consequently, 

 the anterior descent to the rostrum is much less steep. The occiput is 

 low and the upper profile of the skull rises but slightly to the parietal 

 eminence, whence it descends gently and almost uninterruptedly to the 

 end of the snout. In form, the occipital surface resembles that oi-Zaedyiis, 

 but is lower, wider and more quadrate ; it is convex and has a strong 

 median protuberance for the vermis of the cerebellum, while near the 

 dorsal summit is a broad, shallow concavity, which is much more distinct 

 than in the modern genus. The foramen magnum is rather small and 

 considerably wider than high and the occipital crest is not very promi- 

 nent, but more so than in recent armadillos. 



The basioccipital is broad behind, narrowing forward ; it is nearly flat, 

 with a fine, hair-like median keel, very different from the prominent keel 

 and deep lateral fossae of Zaedyus ; the condyles are sessile, transverse 

 and very short ; each is invaded, as in most armadillos, by a sulcus from 

 the outer side and, a more peculiar feature, the medial end is notched in 

 a way that gives a characteristic shape to the foramen magnum ; no par- 

 occipital process is formed. The supraoccipital is broad and low ; its 

 median upper portion is inserted between the diverging ends of the pari- 

 etals and is so reflected as to present dorsally, but is clearly demarcated 



