I2O PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



appearance and proportions. Perhaps some of these modifications will 

 prove to be of specific value, but it will require much more extensive 

 material than has yet been gathered satisfactorily to establish such a con- 

 clusion. In general, the skull has a considerable resemblance to that of 

 Glyptodon, but there are many differences, most of which may be referred 

 to the inordinate increase in the height of the teeth and consequent depth 

 of the jaws in the Pampean type. In proportion to its length, the skull 

 of the Santa Cruz genus is much lower and narrower, the alveolar por- 

 tion of the maxillaries having attained no such development, the rostrum 

 is relatively much longer and narrower and the forehead much less ex- 

 panded, making the postorbital processes and constriction less conspicu- 

 ous ; the curious overhanging shelf within the orbit formed by the parietal 

 and frontal is already indicated, but far less prominent. The occiput is 

 relatively larger and is nearly at right angles to the plane of the upper 

 teeth, while in Glyptodon it is inclined very steeply forward, so as to pre- 

 sent almost dorsally, and at the same time the condyles are raised to a 

 very high level ; the occipital crest is more prominent in the Santa Cruz 

 genus, but is not nearly so thick and massive ; the zygomatic arches arise 

 more anteriorly and lower down on the sides of the cranium and thus are 

 less inclined in their course forward ; the descending suborbital pro- 

 cesses are much shorter and the ascending ramus of the mandible is very 

 much lower. 



In side-view, the upper profile of the skull rises slightly to the parietal 

 eminence and thence descends more or less steeply to the end of the 

 rostrum, with a convexity over the frontals produced by the sinuses, which 

 varies much in prominence. 



The basioccipital is relatively elongate and appears to form nearly all 

 of the visible basicranial axis; it is stout arid broad, and the posterior 

 portion is very wide and deeply incised by the foramen magnum ; the 

 condyles are relatively small, sessile and semicylindrical ; each articular 

 surface is deeply invaded by a sulcus from the outer side. The foramen 

 magnum is broad, but very low, presenting ventrally rather than pos- 

 teriorly. None of the specimens displays the sutures between the ex- and 

 supraoccipitals, but, as a whole, the occipital surface is low and wide and 

 has a more or less distinct median ridge with a deep fossa on each side ; 

 paroccipital processes are entirely wanting. The periotic is quite largely 

 exposed in the occiput and has a rugose surface, but forms no mastoid 



