NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 83 



collection ( No. 43799) shows this form to be represented in the Dad 

 fauna from beneath the Tipton tongue in the Washakie Basin, and 

 two last lower molars from the Cathedral Bluffs tongue above, identi- 

 fied by Morris (1954, p. 197) as Microsus, I cannot distinguish from 

 this tooth in H. pelodes. 



The two jaws from the Knight at Knight Station, earlier referred 

 to Diacodexisf, sp. (1952, p. y2), have since been located in the 

 American Museum collections and found to represent Hexacodus. 

 One of them, A.M. No. 12843, "la-y well be of H. pelodes, to judge 

 by the preserved molar, although P4 is relatively slender and lacks 

 both paraconoid and metaconid, suggesting a distinct species. How- 

 ever, this tooth seems highly variable in H. pelodes, between specimens 

 in which the molars cannot be distinguished. In fact, no two P4's 

 among these have been found that are quite alike. 



Of particular interest is the discovery, in recent collections repre- 

 senting the La Barge fauna, of upper teeth that may belong to this 

 small artiodactyl. One specimen is a maxillary fragment with M^ and 

 M^ (U.S.N.M. No. 22248 ; pi. 14, fig. i) and another an isolated upper 

 molar (U.S.N.M. No. 22434; pi. 14, fig. 3), possibly M\ A second 

 maxilla regarded as belonging to Hexacodus pelodes, found by a 

 University of Wyoming field party (U. of Wyo. No. 1779) in the 

 La Barge horizon, is important in displaying P^ and P* as well as M^ 

 and part of M^ (pi. 7, fig. 2). The premolars are comparatively large, 

 as would be expected from consideration of the large and somewhat 

 inflated lower fourth premolar, and exhibit an enamel rugosity more 

 evident than in the molars. The talon, moreover, is broad and 

 prominent in both P' and P* and has a well-developed deuterocone. 

 No tritocone is present. 



Among other Wasatchian artiodactyls, P^ is known in both Dia- 

 codexis and Wasatchia. In Diacodexis this tooth is much more 

 elongate, anteroposteriorly, and the talon is not nearly so well de- 

 veloped. It exhibits, moreover, a more prominent parastyle and a 

 distinctive tritocone, quite unlike Hexacodus. Sinclair's illustration 

 of P^ (1914, fig. 2) in Wasatchia dorseyana shows this tooth to be 

 relatively small and with little evidence of a talon. P* in No. 1779 is 

 rather less distinctive but in comparison with Diacodexis it is seen to 

 have more inflated cusps with a higher saddle between them. 



Among Bridgerian artiodactyls, P^ is recorded only for Homacodon. 

 This tooth in Hexacodus is more suggestive of Homacodon than it is 

 of Diacodexis, but the anteroposteriorly broader talon and the absence 

 of a tritocone distinguish it from Homacodon. P*, again, is rather less 



