THE HEART MOUNTAIN OVERTHRUST, WYOMING 549 



fossils which are described below were collected from a 50-foot 

 zone of gray, olive, and red clays that are well exposed along a 

 narrow ridge 1,000 feet northeast and 150 feet stratigraphically 

 below the summit. 



The fossils were first referred to J. W. Gidley of the United 

 States National Museum, but, as field parties from the American 

 Museum of Natural History have closely studied and made numer- 

 ous collections from these beds, it seemed advisable to refer the 

 fossils to them also. The statements of Mr. Gidley {a) and of 

 Mr. Walter Granger (h) are attached: 



a) A preliminary report was furnished to Dr. Stanton on November 25 

 (unofficially) . It was as follows : 



" No. I. The largest tooth is a right upper third or last molar oiHelaletes; 

 cf. nanus Marsh. Not known outside the Bridger horizon. 



" No. 2. The next smaller tooth is a last left upper molar of Eohippus sp. 



"No. 3. The fragment of jaw containing two teeth I have not been able 

 to definitely determine." 



In addition, I may now say that a further study of the smaU jaw fragment 

 seems to warrant referring it to Hemiscodon pucillus Marsh, with which it 

 agrees almost exactly in size. This determination, however, cannot be made 

 positive without comparing it with the type, which is probably in the Yale 

 Museum collection. This is a Bridger species. 



It would thus seem that the three specimens represent a Bridger fauna, 

 although the Eohippus tooth suggests Wasatch rather than Bridger affinities. 



h) I have examined the three specimens of mammal teeth from Eocene 

 beds near the top of McCulIock Peak, Wyoming, and submit the following 

 determinations: 



(i) Helaletes, a last upper molar of the right side. 



(2) Eohippus, a last upper molar of the left side. 



(3) Tetonius or Ahsarokius, a fragment of the right mandible, containing 

 the first and second molars. 



The Lophiodont genus Helaletes has hitherto been recorded only from the 

 Bridger, but it might reasonably be expected from the uppermost levels of 

 the Lower Eocene since another Bridger perissodactyl, Hyrachyus, has recently 

 been found in the upper horizon of the Wind River (Lost Cabin beds). 



The Hyracothere tooth shows characters most closely approached by the 

 smaller specimens of Eohippus from the upper Wind River, as well as by 

 specimens from the upper Huerfano, which is now regarded as the probable 

 equivalent of the almost barren Bridger A. 



The tiny jaw fragment of the Tarsiid cannot definitely be assigned to 

 either of the genera mentioned because it lacks the diagnostic front teeth. 



