NO. 8 UPPER EOCENE ARTIODACTYLA — GAZIN 29 



strikingly convex, anteroposteriorly, and the primary cusp and deu- 

 terocone seem pinched together, not at all like other Uintan dicho- 

 bunids. The occlusal surface of this tooth on the left side is not 

 exposed, but the external wall appears comparatively normal; as a 

 consequence, characters exhibited by the right P* probably should not 

 be stressed. If P4, the corresponding tooth below and on the same side, 

 can be regarded as normal, the metaconid is very weak. It represents 

 a stage of development advanced over Homacodon vagans, but ap- 

 parently less progressive in this respect than in Microsus cuspidatus, 

 as observed in referred specimens of these Bridger forms. 



HYLOMERYX QUADRICUSPIS s (Peterson), 1919 

 Plate 3, figure 4 



Type. — Portions of right and left maxillae and rami of the mandible, 

 CM. No. 2346. 



Horizon and locality. — Uinta C, south of Kennedy's hole, west of 

 Dragon- Vernal road, Uinta County, Utah. 



Discussion. — Hylomeryx quadricuspis is the type of the genus 

 Sphenomeryx which is regarded as a synonym of Hylomeryx. The 

 species H. quadricuspis is apparently distinct but very close in size 

 to H. annectens. The anteroposterior dimensions of the upper and 

 lower teeth are about the same in the types of the two species ; how- 

 ever, the upper molars measure a trifle less and the lowers a trifle 

 greater in transverse width than in H. annectens. The principal differ- 

 ences noted include a weaker deuterocone on P^ and a transversely 



MEASUREMENTS IN MILLIMETERS OF DENTITION IN TYPE SPECIMEN OF 



Hylomeryx quadricuspis, cm. no. 2346 



P^ anteroposterior diameter : transverse diameter* 5.9: 4.1 



P*, anteroposterior diameter : transverse diameter 4.9 : 6.10 



M*, anteroposterior diameter : transverse diameter* 5.4 : 6.2 



Lower cheek teeth, anterior margin of alveolus for P3 to posterior 



margin (estimated) of M3 32.00 



Lower molar series, Mi-Ma (estimated), inclusive 19.20 



Pa, anteroposterior diameter 6.1a 



P4, anteroposterior diameter : greatest transverse diameter 5-9 : 3-5 



Ml, anteroposterior diameter : transverse diameter of talonid 5-9 : 3-9 



M2, anteroposterior diameter : transverse diameter of talonid 5.8 : 4.4 



M3, anteroposterior diameter : transverse diameter of trigonid 7.5a : 4.0 



a. Approximate. 



* Measurements of posterior upper premolars are taken anteroposteriorly across outer por- 

 tion and transversely perpendicular to outer margin. Those of upper molars are talcen 

 anteroposteriorly perpendicular to anterior margin and transversely across anterior portion 

 of tooth. 



s Also illustrated in Peterson, 1919, pi. 37, figs. 15-16. 



