Colpodon Gaudry, in part, 1906, Anal. Palaeontologie, t. 1, p. 30. The formula is 3 1 4 3 -------; 3 1 4 3 type species _L. gaudryi_. Of all the animals in the Deseado, this is the most abundant. Using this species as a basis, the following are the characteristic features. The first upper incisor is a small cropping 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 difference, 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 cingulum 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. In the lower dentition, the first two incisors are small cropping teeth, with the anterior face flattened and having a trace of a cingulum; while on the inner face the cingulum is well developed. Incisor 3 is developed into a tush corresponding to inc. 2 in the upper dentition. As in the upper teeth, there are two types, that of _L. oxyrhynca_ with the tush only about twice the size of an incisor, and that of _L. gaudryi_ with it much larger.