214 THE DESEADO FORMATION OF PATAGONIA 



is present and carries a rounded shelf. The paracone is 

 the chief cusp, and is developed as a high central pointed 

 denticle. The metacone is not developed as a cusp, but is 

 represented by a long slanting ridge to the rear, the apex 

 of which has been fused to the paracone. The last upper 

 molar is better developed than in most Santa Cruz genera, 

 consisting of a high median cusp, the paracone; a small 

 anterior cusp, the anterior external style; and a shelf-like 

 posterior cusp, the protocone. Lower premolars 1-3 are 

 simple two-rooted teeth, each carrying a single cusp on 

 the crown. The fourth premolar carries a well marked 

 paraconid in front, a large median protoconid on the rear 

 of which is a tiny metaconulid ; and a tiny talonid or heel 

 w r hich is without a basin and consists of a single tiny cusp. 

 The molars are all of the same character as the last pre- 

 molar. The lower jaws are united by a ligamentous sym- 

 physis. 



Ameghino distinguished four species, P. lacerans, P. 

 tenax, P. mitis, and P. tennis, in the order of their size. 

 The last two are but little known but are quite certainly 

 another genus. 



Pharsophorus lacerans Ameghino 



P. lacerans Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 503. 



The species was founded on a lower jaw with the roots 

 of the incisors, canine, and first two premolars, and with 

 the remaining teeth intact. We did not find the species, 



Fig. 139. Left mandible 1/2 natural size, after Ameghino. 



