MESODONTA. 237 



dedicated to Di*. Victor Lemoine, of Reims, France, well known for his 

 many important discoveries in the lower Eocene formation, and his inves- 

 tigations in various departments of zoology. 



Hyopsodus paulus Leidy. 



Proc. Acad. Phila., 1870, p. 110; 18T2, 20. Report U. S. Geol. Surv. Terrs., I., p. 75. 

 Plate V, figs. 1-9 and 18-22. 



This species is abundant in the Bridger, Washakie, and Wind River 

 Basins, and I have thirty-eight more or less broken mandibular rami from 

 the Big Horn. With all these jaws there is not a single skull or skeleton. 

 I am therefore unable to add anything to Dr. Leidy's description. 



Hyopsodus vicaeius Cope. 



Microsyops vicarius Cope. On some Eocene Mammals obtained by Hayden's Geol. Svirv. of 1872, p. 1, 

 March 8, 1673. Annual Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 609. H. mmmcuUs Leidy. 

 Report U. S. Geol. Surv. Terrs., I, 1873. 



Plate XXIV, figs. 20-21 ; XXVa, fig. 7. 



Founded on portions of the mandibular rami of two individuals from 

 the bad lands of Cottonwood Creek, Wyoming. These represent an animal 

 considerably smaller than the Hyopsodus paulus. The most complete speci- 

 men was obtained from the Wind River region of Wyoming. It includes 

 the dentition of both jaws, excepting the superior canine. 



The three superior incisors are of equal size and have angular spatu- 

 late crowns in contact with each other. The external cusps of the pre- 

 molars are simple. All the superior molars have a weak anterior basal 

 cingulum. The last true molar is but little smaller than the others, and 

 only differs in form in the rather more oblique external border. The infe- 

 rior incisors are closely packed together. The root of the ^canine is not 

 larger than that of the I. iii or Pm. i. The premolars follow the canine 

 and each other without diastemata. The crown of the third premolar is 

 rather obtuse, and has no anterior nor internal tubercle, but has a rather 

 wide heel. The anterior edge of the fourth premolar is curved round 

 abruptly so as to embrace the base of the inner cusp, and does not support 

 an anterior cusp. Heel wide, with a submedian and a lateral keel. The 



