398 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



becoming transversely oval distally ; the cnemial crest is not very prom- 

 inent, but extends very far down the shaft, which is much straighter than 

 in Myocastor. The distal end is not much broadened, but is quite thick 

 and heavy, and the distal fibular facet is extremely small ; the astragalar 

 surface is deeply grooved and asymmetrical, the outer concavity much 

 exceeding the inner in size ; on the posterior side is a very long and 

 prominent intercondylar tongue. 



Little of the pes is preserved, but apparently it was relatively somewhat 

 less heavy and elongate than in Myocastor. The astragalus has a well 

 grooved, asymmetrical trochlea, the outer condyle much exceeding the 

 inner in size ; the neck is quite narrow and depressed, ending in a convex 

 head, upon the tibial side of which the navicular facet is reflected ; the 

 external calcaneal facet is very large, deeply concave and so oblique as to 

 reduce the fibular surface to a narrow band ; this external calcaneal facet 

 is quite widely separated from the narrow sustentacular facet. 



The calcaneum is incompletely known, the tuber not being preserved in 

 any of the specimens, but it evidently had a large dorso-plantar diameter 

 and was laterally compressed ; the external astragalar facet is large and 

 convex and the prominent, heavy sustentaculum bears a small subcircular 

 facet. The distal portion of the calcaneum is elongate and ends in a very 

 oblique concave surface for the cuboid. 



Fragments of the metatarsals indicate that those bones were shorter 

 and heavier than in Myocastor. 



Restoration (Plate LXX). Among modern genera it is the skeleton 

 of Myocastor which displays the greatest resemblance to that of Neoreomys, 

 but there are many differences. In the fossil, the head is smaller and 

 lighter, while the shorter incisor teeth, paroccipital processes and angular 

 processes of the mandible give to the skull quite a different appearance. 

 The neck is more elongated and slender, but the vertebrae of the trunk are 

 quite similar ; the long tail, shown in the figure, is entirely conjectural and 

 may perhaps be incorrect. The limbs are somewhat longer tandheir pro- 

 portions, as well as those of the feet, are rather more like those seen in 

 Agouti than those of Myocastor. 



Relationships. It does not seem at all probable that Neoreomys was 

 directly ancestral to any existing genus. While it resembles the Capro- 

 myince in dentition and skull structure rather more than any other recent 

 rodents, it has also many likenesses to Agouti, Dasyprocta and Dinomys. 



