424 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



pointed and with only a minute cleft at the tip ; the ventral surface is flat 

 and slightly broadened, remotely suggesting the unguals of certain hoofed 

 animals, and the subungual process is only moderately developed ; the 

 claws must have been quite different from those of Erethizon. 



The hind limb is disproportionately longer than the fore and all its ele- 

 ments are much longer. Relatively to the skull, the femur is somewhat 

 shorter than in Erethizon, but is much longer in comparison with the hu- 

 merus. The head is large, hemispherical, set upon a much constricted 

 neck and presenting almost directly inward ; the great trochanter is low, 

 but thick, enclosing a small, deep digital fossa ; the second trochanter is 

 low, conical and so completely posterior as to be concealed when the bone 

 is seen from the front ; there is no third trochanter. The shaft is slender, 

 straight and nearly cylindrical, in marked contrast to the broad, antero- 

 posteriorly compressed femur of Erethizon, and the rotular groove is nar- 

 rower, deeper and has better defined margins than in the latter ; the con- 

 dyles are small and project little behind the plane of the shaft. 



The tibia (Plate LXVII, fig. 2) is rather longer than the femur, thus 

 reversing the proportions of Erethizon; it is very slender and has a slight, 

 though distinct, sigmoid curvature ; the cnemial crest varies in develop- 

 ment in the two species of which the tibia is known, being much more 

 prominent in 6". latidens than in S. varians ; the distal end resembles that 

 of Steiromys, with rather more prominent intercondylar ridge and shorter 

 posterior tongue ; the internal malleolus is almost bisected by a deep ten- 

 dinal sulcus. 



The fibula, the proximal end of which is not known, has an extremely 

 slender, thread-like shaft; the distal third appears to have been closely 

 applied to the tibia, though without ankylosis ; the distal end resembles 

 that of Steiromys rather than that of Erethizon. 



The pes (Plate LXVII, fig. 3) is not unlike that of Steiromys, though 

 with certain noteworthy differences. The calcaneum has a relatively 

 longer and more slender tuber, the free end of which is hardly grooved, 

 and the external prominence near the distal end, for the attachment of the 

 lateral ligament is much less conspicuous. The astragalus has an even 

 more asymmetrical trochlea, the internal condyle being hardly more than 

 a sharp ridge ; the neck has no such strong inclination toward the tibial 

 side, but is nearly in the proximo-distal axis of the bone. The navicular 

 is even narrower in proportion to its length than that of Steiromys and, 



