124 THE DESEADO FORMATION OF PATAGONIA 
Proadinotherium leptognathus Ameghino 
P. leptognathus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 625. 
P. leptognathus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 467. 
Of this species we found on the Chico del Chubut River, 
west of Puerto Visser, three specimens; the back of a skull 
as far forward as molar 2, and two lower 
jaws. In general, the species is very 
similar, even to size, to Adinotherium 
ovinum of the Santa Cruz. 
The upper molars are strongly hypso- 
dont, curved teeth. On the upper surface, 
the basin is subdivided by two strong 
cristae into three smaller bays. In an 
early stage of wear, the second crista 
unites with the posterior lobe, convert- 
ing bay 3 into a pit. On the posterior 
margin of the tooth, the cingulum is de- 
veloped so as to appear like a third crista, 
ig. 81. Left lower je a: ' 
withtineisor sand us” which inclosed bay 4, and when the tooth 
ccammen is worn, bay 4 becomes a pit also. 
In my lower jaw incisor 3 is developed into a strong 
caniniform tush. Most of the teeth are lacking, but 
lower molar 2 is a strongly compressed, hypsodont tooth, 
surrounded by a thick layer of enamel. This tooth rises 
22 mm. above the well-developed roots, and is already 
considerably worn down. ‘The pillar is prominent as a 
strong fold in the middle of the posterior crescent. In 
this specimen there is no trace of the usual pit (3) indi- 
cative of the septum, but I should expect to find it in a 
younger specimen. ‘The mandible broadens in front into a 
scoop-like anterior end, and the alveoli of the first two in- 
cisors would indicate that they were proclivous. The alve- 
oli for the other teeth are aranged as in Adinotherium. 
