EDENTATA OF THE SANTA CRUZ BEDS. 



163 



continuous series, but more commonly the first tooth in each jaw is 

 separated by a diastema from the succeeding ones and is more or less 

 caniniform ; almost always this tooth differs from the others in shape, 

 being usually cylindrical, or obscurely trihedral, and quite small. Some- 

 times, however, as in Eucholceops, it is a formidable weapon, like the tusk 

 of the Pampean Lestodon, and in Megalonychotherium it is much enlarged 

 and laterally compressed. One specimen has been found in which A is 

 transversely grooved by attrition, but this is probably abnormal, as the 

 tooth is otherwise of the Usual shape. The first upper tooth is always 

 confined to the maxillary and may be inserted near the anterior border of 



FIG. 15. 



Lower teeth of Santa Cruz Gravigrada, x ^. a, Hapalops longiceps ; b, H. indifferens ; c, 

 H. clongatus ; d, Eucholaops fronto ; e, Pdecyodon arcuatus ; f, Prepotherhtm moyani ; g, Nema- 

 therium sp. 



that bone, or far behind it. When the jaws are closed, T always passes 

 behind -, showing that the former at least cannot be a true canine. Ex- 

 cept in the Mylodontidce, the grinding, or molariform, teeth are of trans- 

 versely oval, rectangular, or subtrihedral form, with two cross-crests and 

 deep intervening valley produced by the abrasion of the opposing teeth, 

 and of course absent in very young stages. In the Mylodontidce several 

 of the teeth have already become angular and lobate, but with an extraor- 

 dinary variability of form. As in the Pampean genera, the teeth have an 



