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, 

 wi&d^Ldmoiir^ which inclosed bay 4, and when the tooth 



— 1/2 natural size. • 1 •, , 



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. 



