10 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. G3. 



VI. Paraconids internal, more or less connate with metaconida, metaconids nearly 

 opposite protoconids, no metastylids; m^ unreduced. One enlarged incisor, 

 the second, if present, vestigial. Canine of moderate size. Jaw moderately 

 slender, front teeth semierect. Premolars two-rooted, anterior ones decidedly 

 smaller than P4. 



1. M3 with enlarged heel, paraconids vestigial except on m^. Premolars re- 

 duced to three, p^ with triangular base, well developed heel, but no metaconid. 



Paromomys. 



2. M3 with slightly reduced heel; paraconids distinct. Premolars reduced to 

 two; p4 with short, basined heel, and with small though distinct metaconid 

 and incipient paraconid .^. Palaechihon. 



ELPHIDOTARSIUS, new genus. 



Genotype. — ElpMdotarsius Jlorencae, new species. 



Diagnosis. — Lower molars of Tetonius type. M3 unreduced, mj 

 and nig short and wide; the outer cusps, especially of the trigonids, 

 set well in from the margin; paraconids distinct and internal on all 

 the molars; subconnate on m^ and mg; metaconids more posterior 

 than protoconids, especially on m.^; p^ enlarged, wedge shaped, with 

 quadrate base. (Anterior teeth and upper dentition not known.) 



ELPHIDOTARSIUS FLORENCAE, new species. 



Plate 4, Figure 2. 



Type. — Portion of a left lower jaw carr3nng four teeth, P4 to nig. 

 (Cat. No. 9411, U.S.N.M. Coll.) Collected by J. W. Gidley. 



Locality and liorizon. — Fort Union "No. 2," "Gidley Quarry," 

 Sweet Grass County, Montana. 



Specific characters. — Size about one-third smaller than Tetonius 

 liomuncuLus. Mj to m3 = 4.5 mm., p^ to m3 = 6.2 mm., length of m3 = 

 2 mm., paraconids internally placed about as in T. homunculus, but 

 somewhat more distinct, decidedly more distinct than in Ahsa^roMus 

 ahhotti; metaconids distinctly more posterior in position than proto- 

 conids. 



The modification of p^ is peculiar in that its summit is made up of 

 three cusps of subequal size and height, arranged almost in line, giving 

 it a bladelike appearance similar to the P4 of Uintanius as described 

 and figured by Matthew. In addition to the cusps of the trigonid of 

 P4 there is on its anterior border a small cuspule situated slightly be- 

 low its summit, and there is a strong but relatively very short heel 

 cusp. 



The lower molars of E. -fiorencae resemble those of AhsaroHus in 

 having the outer cusps set far in from the margin, and those of Teto- 

 nius in the relative width of their crowns, which in nij and m.^ slightly 

 exceeds their length. They also resemble those of the Eocene genera 

 in that the height of the crowns progressively increases from back to 



