110 THE DESEADO FORMATION OF PATAGONIA 



Using this species as a basis, the following are the charac- 

 teristic features. The first upper incisor is a small crop- 

 ping tooth, with a well-developed cingulum high up on 

 the inner face, which, when the tooth is worn down to the 

 proper level, unites with the main part of the crown and 

 incloses for a short time a small pit. On the external face 

 there is also a feeble cingulum near the base of the enamel. 

 The second incisor is greatly enlarged into a caniniform 

 tush. In the species L. oxyrhynca, this tooth is much 

 smaller but as this reduction of the tushes is the only dif- 

 ference, I consider these forms as the female. The third 

 incisor is again small, and has a well-developed cingulum 

 on both the front and inner faces. The canine is similar 

 to inc. 3. 



The first premolar is much reduced in size, with a weak 

 cingulum on the outer face, and probably another on the 

 inner side (the tooth is too much worn in my specimen to 

 be sure). Beginning with premolar 2, the upper teeth are 

 molariform. The premolars are rectangular in outline, 

 each being much wider than long, and each having a cingu- 

 lum on the outer side. On the inner side, along the anterior 

 half of each premolar, there is a high cingulum, which, 

 though interrupted at the anterior corner, continues around 

 onto the anterior face of the tooth. On a worn tooth this 

 anterior cingulum unites with the grinding surface, and 

 leaves a small pit in the anterior internal corner, which is 

 very suggestive of Rhynchippidae. In the middle of the 

 grinding surface, there is an oblique pit, the remains of the 

 basin in young teeth. The molars continue to increase in 

 size toward the rear. They have a vestige of a cingulum on 

 the external side, no cingulum on the inner side, but on the 

 anterior side for about one third the distance there is a 

 cingulum similar to that on the premolars. In the middle 

 of the grinding surface is an elongated oblique pit, similar 

 to that in the premolars, but a little more advanced, there 

 being a trace of the development of cristae. 



