82 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 28 



of a better-developed tritocone than in Leptoreodon. In the lower 

 jaws both P3 and P4 have an anterolingually directed crest from the 

 protoconid, but in Leptotragulus the anterior extremity is more 

 sharply flexed with a better-defined parastylid. A posteroexternal 

 crest extends from the protocone, then swings inward forming the 

 posterior crest of the heel. A posterointernal crest extends posteriorly 

 and only slightly inward from the apex of the protoconid but termi- 

 nates before reaching the posterior crest, leaving the talonid basin 

 broadly open lingually. In some material of Leptotragulus this talonid 

 basin of P4 may be partially constricted medially by a slight plication 

 from the posterointernal crest. In Leptoreodon there is a prominent 

 metaconid posterointernal to the protoconid in P4 and apparently also 

 in P3. Moreover, P4 of Leptoreodon exhibits a usually distinctive, 

 though variably developed, entoconid. In Leptomeryx the entoconid 

 is well developed, and in P4 joins the metaconid in early wear, but 

 in P3 joins the external crest well back of the protoconid. It may be 

 further noted that the upper molars in Leptomeryx have a noticeably 

 more oblique appearance than in the Eocene forms. 



LEPTOTRAGULUS PROAVUS " Scott and Osborn, 1887 

 Plate 18, figure i 



Synonyms. — Parameryx laevis Marsh, 1894. 



IParameryx sulcatus Marsh, 1894. 



Type. — Anterior portion of the left ramus of a mandible with P4 

 and Ml, P.U. No. 11501. 



Horizon and locality. — Uinta upper Eocene, "White River," Uinta 

 Basin, Utah. 



Discussion. — The gentoype, Leptotragulus proavus, is much the 

 larger of the three Eocene species now recognized and is represented 

 in collections by a relatively small amount of material. The premolars 

 are relatively elongate and P4 has a distinctive, lingually placed, nearly 

 conical parastylid. The posterolingual crest swings slightly inward 

 with a weak suggestion of a metaconid nearly halfway down its slope, 

 and there is a slight plication from this crest directed toward the mid- 

 dle of the talonid basin. Mi shows a prominent accessory cusp or 

 pillar between the protoconid and hypoconid. 



The cotype lower jaw material of Parameryx laevis, which exhibits 

 part of Ml and M2, corresponds in all details to the Mi in L. proavus. 



The Chadron form Leptotragulus profectus Matthew, from Pipe- 



** Also illustrated in Scott, 1889, pi. 7, figs. 10, loa. 



