GLIRES OF THE SANTA CRUZ BEDS. 465 



termine whether they are perforated so as to communicate with the orbits. 

 This skull agrees with that of Dolichotis in the moderate size of the fora- 

 men lacerum medium, there being no such great vacuity at this point as 

 occurs in Cavia. 



The mandible has a general resemblance to that of Dolichotis, but, as 

 Ameghino has pointed out, Eocardia differs from all the existing mem- 

 bers of the family in the position of the masseteric crest. In the recent 

 genera the crest has a very elevated position and an almost horizontal 

 course, with a deep groove between itself and the alveolar border, but in 

 the fossil the crest is much lower down on the jaw and runs obliquely 

 downward and backward, forming the ventral border of the angle. The 

 coronoid process, though very much reduced, is better developed than 

 in Dolichotis and rises higher than in Cavia, though, owing to the shal- 

 lowness of the sigmoid notch, it appears to be shorter ; the condyle has 

 much the same shape as in the former, as has also the masseteric fossa. 

 The angular process has been broken and lost from all the specimens. 

 The horizontal ramus is quite stout and its ventral border has several 

 protuberances for the teeth, which, however, are far less conspicuous than 

 in Dolichotis ; the symphysis is shorter and less procumbent than in the 

 latter, the chin rising much more steeply. 



Vertebral Column and Ribs (Plate LXXI). The neck is rather short 

 and slender. The atlas is short, broad and depressed, without neural 

 spine and with only a vestige of the hypapophysis ; the transverse pro- 

 cesses also are short in both dimensions and are less produced behind 

 the posterior cotyles than in Dolichotts. The neural spine of the axis is 

 relatively considerably smaller than in the latter, but of not dissimilar 

 shape ; the centrum is short and much depressed, the cotyles for the atlas 

 rising high upon the sides of the large neural canal. The other cervicals 

 are small and lightly constructed, but without other peculiarity than the 

 absence of neural spines from the third, fourth and fifth. 



The number of trunk vertebrae has not yet been definitely determined, 

 though there is reason to believe that it was the same as in Dolichotis, 

 Th. 12, L. 8, but, owing to the disparity in the length of the fore and hind 

 limbs, the curvature of the back is different. In the anterior part of the 

 thoracic region the neural spines are considerably shorter than in the 

 recent genus, are very slender and have a strong backward inclination ; 

 posteriorly the spines diminish in length and increase in width, while the 



