1902.] 



Matthew, The Skull of Hypisodus. 



315 



portionately larger, longer, and more complicated; antero- 

 internal cusp of p^ less prominent, posterointernal (hyposty- 

 lid) more so; hypoconid ridge bifid posteriorly, into a 

 posterior branch which passes backward to the posterior 

 margin, and a posterointernal branch projecting into the 

 basin of the heel. Pj more anterior in position than in L. 

 evansi, probably near anterior end of diastema, while in 

 L. evansi it is nearer to pg than to Cj . 



Hypertragulus Cope. 



Dentition, I-' C\ P| Mf. Lower canine incisiform, first premolar 

 large, fully caniniform, with a short diastema in front and a long one 

 behind. Upper canine enlarged, first upper premolar two-rooted, with 

 diastema before and behind. Second lower premolar spaced, simple, 

 without accessory cusps; third with heel; fourth with anterior cusp 

 and heel; but all though equally trenchant simpler than the corre- 

 sponding teeth in Lepto- 

 nieryx. Second upper pre- 

 molar simple, two-rooted; 

 third with internal cusp; 

 fourth with two crescents. 

 No mesostyle on upper mo- 

 lars. Heel of last lower 

 molar composed of two 

 equal opposite crescents. 

 Molars somewhat more hyp- . 

 sodont than those of Lepto- 

 meryx. 



Skull much like that of Leptomeryx, but somewhat shorter, muzzle 

 slenderer, supraorbital ridges much more prominent. Prelachrymal 

 vacuity as in Leptomeryx, bullae somewhat larger.' 



Ulna and radius coossified; tibia coossified with distal end of fibula; 

 navicular and cuboid united. Manus of four separate usable digits; 

 pes with two separate digits and sphnts representing the lateral meta- 

 tarsals. 



Fig. 3. Dentition of Hypertragulus. 



' In his recent discussion of this genus Prof. Scott interprets the dentition as 

 Ij CJ PJ M3, the first premolar absent and lower canine caniniform. It would appear 

 rather that, as in most other selenodonts, the canine is incisiform. The number of in- 

 cisors is not certainly known; but it seems certain that both in the John Day skulls on 

 which Prof. Scott's description and figures were based, and in the White River skulls in 

 the Amer. Mus. collection, the inferior tooth, which Prof. Scott considers as a canine, 

 closes behind, not in front of, the upper canine; his drawing does not agree with the 

 specimen in this respect. The one skull from the White River in which this part is 

 preserved shows the lower caniniform tooth shutting unmistakably behind the upper 

 canine; it is, therefore, a premolar, and the canine is incisiform as in Leptomeryx. 



