452 PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 



but has much the same shape. The incisive foramina are larger and the 

 premaxillary spines are broader than in the latter, and, in some species at 

 least, there is an opening in the median line, between the premaxillaries 

 and in advance of the incisive foramina, as is also the case in Perimys 

 and Viscaccia. Nearly the whole of the hard palate is made up of the 

 wedge-like palatines, the maxillaries having practically no palatine pro- 

 cesses ; the median ridge and posterior spine of the palatines are quite as 

 in Viscaccia. 



In all the examples of the mandible that I have seen the ascending 

 ramus is lacking, and nothing is known of the condyle, coronoid or angle. 

 The horizontal ramus is very much like that of Viscaccia and differs from 

 that of Perimys in the small size of the masseteric crest and fossa, but the 

 symphysial region is somewhat shorter and less procumbent than in the 

 modern genus, the ventral border inclining more steeply upward. The 

 ventral surface in this region has the same finely punctate appearance as 

 in Viscaccia, but the punctate area is extended farther back along the 

 whole length of the incisive alveolus. 



A few fragments of the hind limb have been found in association with 

 P. divisits; these differ from the corresponding parts of Perimys in their 

 relatively much greater size, in which respect they even surpass those of 

 Viscaccia. The ilium has its principal diameter directed more dorso- 

 ventrally than in the latter; the peduncle is shorter and the anterior 

 expansion greater and more abrupt, and the ilio-pectineal process is decid- 

 edly better developed, while the prominent acetabular border, so far as it 

 is preserved, pursues a somewhat less oblique course ; the iliac surface is 

 quite broad. 



None of the fore limb bones has yet been found, so that it is not possible 

 to make any direct comparison between the fore and hind limbs. How- 

 ever, as the femur and tibia are far larger in proportion to the size of the 

 head than in Perimys, it may be inferred that the difference in the relative 

 lengths of the fore and hind limbs was at least as great as in Viscaccia. 



The femur differs in several respects from that of Perimys, in which 

 respects it approximates that of the recent genus. As already mentioned, 

 it is relatively even larger than in the latter, but as Prolagostomus was 

 actually a much smaller animal, the relation may be as well expressed by 

 saying that the head is proportionately smaller in the latter. In propor- 

 tion to its length, the femur is more slender than in Viscaccia; the head 



