222 THE DESEADO FORMATION OF PATAGONIA 



or last. Our specimen shows pm. 3 and 4 and the three 

 molars. The third premolar is a small two-rooted tooth 

 with a simple crown and no heel. Premolar 4 is an en- 

 larged sectorial tooth, the anterior part consisting of two 

 cusps, closely set near the median line, with an incipient 

 cusp on the inner face of the large anterior cusp. The 

 posterior part of this tooth is arranged as a typical talonid, 

 with one internal and two external cusps on the margin of 

 a shallow inclosed basin. On the rear of the tooth is a 

 small crescent-like cingulum, which occurs in the same place 

 on molars I and 2, but is lacking on molar 3. This is a 

 characteristic feature of the genus. On the anterior part 

 of the molars is developed a sort of trigonid of small size, 

 and the cusps are indistinct. The posterior portion of each 

 molar is a large talonid with a shallow basin surrounded by 

 a low wall on which are three tiny cups (the entoconid, 

 hypoconid, and hypoconulid). 



Pilchenia lucina Ameghino 



P. lucina Amegh., 1903, Anal. Mus. Nac. B. A., ser. 3, t. 2, p. 128. 

 P. lucina Amegh., 1904, Anal. Soc. Cienc. Rep. Argen., t. 58, p. 259. 



In the Deseado beds, on the Chico del Chubut River, 

 west of Puerto Visser, we found a single specimen of this 



Fig. 146. Left mandible with premolar 3 to molar 4 4 times 

 natural size. 



species which agrees with the single tooth figured by Ameg- 

 hino as the type, and which I interpret as molar 3. The 

 description is given under the genus, the measurements 

 are as follows: 



