42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



PARAHYUS VAGUS is Marsh, 1876 



Type. — Right ramus of mandible with P3-M3, Y.P.M. No. 10972. 



Horizon and locality. — The type was described by Marsh as coming 

 from the lower Eocene of Wyoming. This, however, I cannot believe, 

 as Parahyus vagus is clearly and in every respect at a stage of de- 

 velopment intermediate between Bridger Helohyus lentus and Washa- 

 kie B or Uinta B Achaenodon insolens. Moreover, during an in- 

 tensive field program involving the lower Eocene of southwestern 

 Wyoming in the past several years, no further evidence has been 

 discovered of such a form in the Wasatchian. With the help of Dr. 

 J. T. Gregory, I have carefully gone over the data which accompanied 

 the material in the Marsh collection and have extracted the following 

 information from the labels : The tray label for the type of P. vagus 

 bears the information "Lower Eocene Washakie?, Coryphodon zone, 

 Wyoming Bitter Creek Station" ; the old exhibition label — "Eocene 

 (Bridger), Bitter Creek Station, J. Heisey Coll. 1876"; and the 

 shipping label — "Bitter Creek Station, Formation ash color, 200 feet 

 above coal, July 8, 1876, J. Heisey." The information gained here is 

 completely confusing, but the principal evidence is that the specimen 

 was included in a shipment made from Bitter Creek Station. Refer- 

 ence to Washakie in one case and Bridger in another is somewhat 

 reassuring, but that pertaining to "Lower Eocene," "Coryphodon 

 zone," and "200 feet above coal" is rather imperiling. It should be 

 noted that the description of Parahyus vagus accompanied that of 

 Eohippus pernix, and the latter undoubtedly came from the lower 

 Eocene near Bitter Creek, as did Cope's Coryphodon armatum. It 

 seems almost certain that the P. vagus specimen was confused with 

 materials collected at Bitter Creek, but actually came from the 

 Washakie beds farther to the southwest of there. Bitter Creek Station 

 was likely the shipping point for much of that general region. It 

 did not, of course, come from Evanston, Wyo., as implied in Matthew's 

 1899 tabulation. 



Parahyus vagus is apparently, though not necessarily, too advanced 

 for Bridger D, so that in all probability the occurrence was high in 

 Washakie A or nearly transitional to Washakie B. 



Discussion. — As noted above, Parahyus vagus is about intermediate 

 between Helohyus lentus and Achaenodon insolens in size. This is 

 the only known valid species, as the upper molar described by Marsh 

 in 1894 as Parahyus aherrans belongs to Helohyus. Structurally, the 

 P. aherrans tooth is entirely like upper molars of Helohyus plicodon, 



18 Illustrated in Peterson, 1919, fig. 12. 



