56.(1181:78.7) 
Article XIV.— A REVISION OF THE LOWER EOCENE WASATCH 
AND WIND RIVER FAUNAS. 
By W. D. MatTTrHew and WALTER GRANGER. 
PART IV.— ENTELON YCHIA, PRIMATES, INSECTIVORA (PART). 
By W. D. MATTHEW. : 
OrDER ENTELONYCHIA. 
Fam. ?ISOTEMNID. 
Arctostylops steini gen. et sp. nov. 
PratTe XV, 
Molar pattern much as in Notostylops, but crowns much higher and narrower, 
heel longer, trigonid more reduced. P, submolariform, Ps; nearly simple, trenchant. 
Size minute, ps-m; = 18 mm. 
Lower Gray Bull beds, Clark Fork basin, Wyoming. 
Type, No. 16830, a lower jaw with ps—m; perfect and unworn. 
The discovery of a Notoungulate mammal in the North American 
Eocene was so completely unexpected that the evidence requires critical 
sifting before acceptance. 
In order first to verify the discovery and to exclude the possible sug- 
gestion that the specimen might have-been secured by Mr. Stein when with 
Dr. Loomis’s expedition to Patagonia a few years earlier, and by some 
accident mislaid and subsequently mixed up with his Bighorn basin col- 
lection, I obtained from him and from his assistant Mr. ‘Turner detailed 
accounts of the exact locality and circumstances of the discovery. While 
it is unnecessary to spread these letters upon the record they are sufficient 
to render it absolutely certain that no such confusion occurred, that the 
specimen here described and figured was found by Mr. Stein in the upper 
part of the Wasatch exposures of Clark Fork basin. 
It will be obvious that the teeth bear no resemblance to any northern 
eroup of mammals, living or extinct. They are not of a primitive but of a 
highly specialized type. There is one and only one of the larger groups of 
mammals which shows in multiform variations this peculiar fundamental 
pattern in the molars. This is the Notoungulata, including under that 
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