Propyrotherium is a smaller form from the Astraponotus beds, apparently a good genus; the type species being P. saxeum, of considerable smaller size than any of the Deseado species. The distinctive features of the genus can not be given until more material is known.

Carlozitteli is based on a small form from the Casamayor with narrow molars. An incisiform tush is associated with the molar, which, if correctly associated, would indicate a wide deviation from Pyrotherium, and would probably be an ancestral form. A second species is reported from the lower Deseado beds, but I am a little skeptical as to the horizon.

Pyrotherium Ameghino

The type species of the genus is P. romeri, which is however a rare species, most of the material and the best known belonging to P. sorondoi. The Amherst Collection contains a skull, complete except that the top of the brain case is crushed in and the parietals lost; a second skull with the full upper dentition but lacking the cranium; four lower jaws; two isolated tushes; the atlas, axis, and cervicals 3 and 4; the humerus; the proximal end of the femur; and part of the front foot; all from the Chico del Chubut west of Puerto Visser. Gaudry had upper and lower dentition and the fore and hind limbs except the feet. Ameghino described the upper and lower dentitions and a fore foot, so that with our material we now have a basis for a fairly complete discussion, the vertebral column being the major part which is still lacking.

The first striking feature is the dental formula. As formerly given, it is inaccurate, there being two great tushes on either side of the upper jaw, instead of one, as described. At first sight, I thought it might be a meristic variation, but both of my skulls show the same arrangement on both sides, and these are the first two skulls which have been found complete to the front end, and neither is by any means a young individual. The dental formula would then read

Upper incisor 1 is a rootless, permanently growing tush about a fourth smaller than inc. 2, but of the same character, being oval in cross section and having enamel on the front face only. These first incisors are directed downward, so that their ends stand between and very slightly in front of the second incisors. The end of each is worn bluntly round in contrast to the beveled end of inc. 2. The second incisor is larger, rootless, and permanently growing, with a hollow base, enamel on the front face only, and oval in cross section. Both these teeth have a layer of cement on them, extending some distance beyond the alveolus. The tips are worn in a long bevel on the posterior side, very much as is the case on the incisors of rodents.

The third upper incisor, the canine, and premolar 1 are lacking, a long diastema occupying their place, out of which they have been crowded by the development of the enormous root of inc. 2, which extends 150 mm. and more back into the jaw. P. romeri is distinguished from the others by pm. 1 being present.

The teeth of the upper premolar-molar series have their crowns expanded, and the two series of either side have moved toward each other; until in front they are in contact while in the rear they are only 50 mm. apart, narrowing the palate in a unique manner, and giving the impression that the palate is mostly a grinding surface. The premolars are completely molariform and the whole series is at an advanced stage of specialization.