164 THE DESEADO FORMATION OF PATAGONIA 
Pyrotherium Ameghino 
Pyrotherium Amegh., 1889, Actas Acad. Nac. Cienc. Cordoba, t. VI, p. 617. 
Pyrotherium Lydekker, 1894, Anal. Mus. La Plata, Palaeontologia Argentina 
pt. 3, p. 4. 
Pyrotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 609. 
Pyrotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 441. 
Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 19-43. 
Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p. 223-4. 
Pyrotherium Gaudry, 1909, Anal. Palaeontologie, t. 4, p. 1-28. 
Parapyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. I, p. 
29. 
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 
crevicals 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 dasis 
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 arrange- 
ment 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 +234. 
Upper incisor 1 is a rootless, permanently growing tush 
about a fourth smaller than inc. 2, but of the same 
