70 Bulletin American Museum of Natural History. [Vol. XXXIV, 
Prolimnocyon robustus sp. nov. 
A considerably larger species is indicated by a part of a lower jaw, No. 
Fig. 62. Prolimnocyon robustus, lower jaw fragment, type specimen, external view 
with crown and inner views of teeth, all natural size. Lower Gray Bull beds, Big Horn Basin. 
15168, from the Big Horn Basin, Gray Bull beds. The larger size, deeper 
jaw, less relative reduction of m3 indicate its distinctness. 
Prolimnocyon antiquus sp. nov. 
Type, No. 14768, lower jaw with teeth mostly broken off, from the Lost Cabin 
horizon in the Wind River Basin. 
Distinctive Characters: Size of P. atavus or slightly larger; ms one-rooted. 
Fig. 63. Prolimnocyon antiquus, lower jaw, superior and external views, natural size. 
Type specimen, Lost Cabin beds, Wind River Basin. 
This species is represented only by the type and doubtfully by No. 2971, 
but the small round alveolus for ms; is so clearly distinct from anything in 
