480 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



The lower premolar (fig. i i rf ) is, strange to say, less completely molari- 

 form than in Eocardia; the external valley which separates the prisms is 

 not continued for the whole height of the crown, but is, in not very 

 advanced stages of wear, converted into a central lake and is then worn 

 away entirely. The molars resemble those of Eocardia, but, so far as I 

 can make out, there is no cement in the valleys of either upper or lower 

 teeth. 



The milk premolars (Plate LXVIII, figs. 26-26") differ from those of 

 Eocardia principally in being rootless ; dp 1 resembles its successor, includ- 

 ing the external accessory valleys, but dp T is more complex than p T and 

 is much more elongate antero-posteriorly ; the anterior prism is subdivided 

 by a second external valley, which is shorter and shallower than the 

 principal one and, in the stage figured, is reduced to a mere notch of the 

 grinding surface. 



The skull (Plate LXIX, figs. 11-12) resembles that of Dolichotis even 

 more than does that of Eocardia, especially in the breadth of the cranium, 

 the large size of the orbit and the manner in which the face is bent down 

 upon the cranial axis, so that the palate is not parallel with that axis, but 

 forms an obtuse angle with it ; this flexure is, however, less than in 

 Dolichotis. The occiput (fig. 12*) is lower and wider than in the last- 

 named genus, narrowing less toward the summit, and the foramen magnum 

 and condyles are correspondingly lower and wider; the paroccipital 

 processes are similar, except for being much more slender; the supra- 

 occipital is much less extended upon the cranial roof. The parietals have 

 much the same broad and vaulted appearance as in Dolichotis, but the 

 upper contour of this region does not descend so much from the coronal 

 suture to the occipital crest, which is principally due to the less pronounced 

 character of the cranial flexure ; the sagittal crest is relatively somewhat 

 longer than in the modern genus, but is very low and inconspicuous. The 

 tympanic bullae are smaller than in the latter, especially in the transverse 

 diameter, so that they narrow the basicranial axis less. The periotic is 

 almost identical in shape and relations with that of Dolichotis, but the part 

 left uncovered by the supramastoid process of the squamosal is somewhat 

 larger and more inflated, and the mastoid process, though very small, is 

 less reduced. 



The squamosal, though very much like that of Dolichotis, differs from 

 it in a number of details ; anteriorly, it is much less extended along the 



