F. B. Loomis — Hyopsodidm. 419 



The olecranon process of the ulna is long (distinctly an Insec- 

 tivor character), and the greater sigmoid cavity is very wide, 

 the less sigmoid cavity being also well marked. The femur is 

 short, thick and flattened, and has a strong third trochanter. 

 (This is not found in Primates, but is especially well marked 

 in Irinaceus.) Finally, according to Wortman, the metapo- 

 dials are short and stout, and the hallus not opposable (both 

 Insectivor features). 



Hyopsodus simplex sp. no v. 



The specimens of this, the smallest and at the same time 

 most abundant of the Wasatch species, were referred by Cope 

 to H. vicarius and H. paulus^ both of the Bridger horizon. 

 Osborn* provisionally referred them to H. mitioulus Cope, 

 from the Sew Mexico Wasatch, but differing from H. simplex 

 in being somewhat larger and having a low (" Esthy onyx-like ") 

 heel and in having the posterior cusps more developed. 



For a type, a lower jaw of the left 

 side carrying the fourth premolar and jj8ft9ftTR3JB\ 

 the molars is chosen. All the teeth of ^WSBP^WSB^ 

 the lower jaw are short and wide with FlG< 3> Hyopsodus sim . 

 obtuse cusps. On each there is a trace piex. Left ramus, xf. 

 of a cingulum about the rounded ante- 

 rior outer corner of the tooth and also externally between the 

 cusps. On the wide fourth premolar the protoconid is better 

 developed than the deuteroconid, and behind there is a wide 

 basin, the posterior margin of which is crenulated. On molars 

 one and two the protolophid is well developed, while there is 

 not more than a trace of a metalophid. A strong ridge runs 

 from the hypoconid to the metaconid. The entoconid is weak 

 and has a small tubercle in front of it, very characteristic of 

 the species. On the last molar the heel region consists of a 

 basin bounded behind by a high crenulated rim, on which the 

 hypoconulid and entoconid appear as crenulations, scarcely 

 larger than the others. 



Each of the upper molars has the cingulum in front, outside 

 and behind. The last of these molars is much reduced and is 

 without a true hypocone. Promolars three and four have each 

 an internal cusp, while the front two are simply cusps. 



Affinities — H. simplex is about the same size as H. vicarius 

 from the Bridger, but the molars are shorter and more robust, 

 while the hypoconulid is less developed and has an extra 

 tubercle in front of it. II. paulus is a much larger and better 

 developed species. H. miticulus is the nearest form, the more 

 specialized and low talonid, and the superior size distinguishing 

 it from H. simplex. 



*Bull. Amer. Museum Nat. Hist., xvi, 183, 1902. 



