SUBORDER B TOXODONTIA 237 



Argyrohippus Ameghino. Teeth with thick cement covering. Stylhippus, 

 Perhippidium Ameghino. Miocene ; Colpodon beds. 



Eomorphippiis and Interhippns Ameghino. Oligocene ; Astraponotus beds. 



Family 2. Nesodontidae Murray. 



• Teeth usually in a compact row. P and I^ enlarged, I^ chisel-shaped, 

 with enamel covering only on the anterior surface, P triangidar, without enamel on 



Fig. 321. 



Nesodon ivibricatus Owen. Upper Miocene (Santa Cruz beds), Patagonia. Skull and lower jaw. i/g. 



posterior stirface. P, C and P^ small, gradually m,erging into and becoming similar 

 to the other prem,olars, and separated from one another by short vacant spaces. Lower 

 incisors chisel-shaped, I^ enlarged. Upper premolars and molars increasing in size 

 posteriorly, prismatic, having enamel only on the outer and front surface, strongly 

 bent inwards, the inner side of the two transverse ridges becoming fused as they 

 are worn down, and surrounding an island. Lower molars with enamel only on the 

 outer and inner surfaces and very strongly compressed. Teeth developing roots only 

 in old age, and then only partially. 



Nesodon Owen (Gronotherium, Phobereotheriiim, Ameghino) (Figs. 321-323). 

 Larger than a tapir and one of the most abundant mammals in the Miocene 

 of Santa Cruz. Patagonia. iV. imbricatus Owen. 



Stenostephanus Ameghino. Imperfectly known, Miocene and Pliocene. 



Trigodon Ameghino. With horn - like excrescence on the forehead. 

 Pleistocene of Monte Hermoso. 



Adinotherium Ameghino (Figs. 318, 320). Upper I^, C and P^ very- 

 small. Miocene ; Colpodon beds and Santa Cruz beds. A. (Nesodon) orirmm 

 Owen. 



Pronesodon, Proadinotherium Ameghino. Miocene ; Pyrotherium and Col- 

 podon beds of Patagonia. 



Acrotherium Ameghino. Similar to Adinotherium. Miocene of Santa Cruz. 



