164 



PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



external covering of cement, which is considerably thinner than in the 

 former, enclosing harder and softer dentine : the different tissues are usu- 

 ally very clearly distinguishable on the worn surfaces. Without excep- 

 tion, the teeth are rootless and remain so throughout life. 



(4) The skull, which is curiously small in proportion to the size of the 

 animal, is of quite a constant type throughout the order, though vary- 

 ing much in details, especially in its relative length and in the elongation 

 of the rostrum. In form the skull is long, low and more or less cylin- 

 drical, with well arched and quite capacious cranium ; the occiput is low 



FIG. 16. 



Skulls of Santa Cruz Gravigrada, x ^. a, Hapalops longiceps ; b, H. elongatus ; c, Mega- 

 lonychotherium atavus ; d, Analcimorphus giganteus ; e, Schismotherium splendens ; f, Pelecyo- 

 don cristatus ; g, Planops magnus. 



and broad and either vertical, or but very slightly inclined forward ; the 

 occipital and sagittal crests are never very prominent and may, especially 

 the latter, be entirely absent, but the cranium never has the broad, flat 

 top, produced by the development of the parietal sinuses, which is seen in 

 the great Pampean genera. There is a distinct, but not deep or abrupt 



