LOPHIODOXTID^. 6 19 



terrupted cross-crests; last with heel. Fourth premolar with but one poste- 

 rior cusp. Skeleton unknown. 



From specimens of the Hyracotherium tapirinum ni. brought from the 

 Big Horn region I learn that tlie dental system is different from that charac- 

 terizing the species of Hyracotherium. There is no diastema posterior to the 

 superior canine, while in the latter genus there are two. Anterior to the 

 superior canine there is a considerable one in the Hyracotherium. This part 

 is not preserved in any of the specimens of S. tapirhium. The characters 

 mentioned have induced me to separate the latter as a type of a distinct 

 genus, Sysfemodoii. The position of this genus is at the base of the Lophi- 

 odontidce, as regards its dental characters, since the continuous dentition is a 

 primitive condition as compared with the presence of the diastemata seen in 

 Hyracotherium. An examination of the figures and descriptions given by 

 Dr. Lemoine of his Pachynolophus gaudryi found by him in the neighborhood 

 of Reims, shows that it belongs to the genus Hyracotherium. It is therefore 

 distinct from either of the species of Systemodon, and is to be compared 

 with the H. craspedotitm of the Wind River country, with which it agrees 

 in size. 



Two species of the genus are known, both from the Wasatch formation. 

 They differ as follows: 



Largestj superior molars .032; premolars .030; internallobe of second sui)erior large. 



8. tapirinus. 

 Smaller; superior molars .030; premolars .025; internal lobe of second superior small. 



/S'. semihians. 



Systemodon tapirinus Cope. 



Paleontological Bulletin No. 34, p. 183, 1881. Aineiican Naturalist, 1831, p. 1018. Hyracotherium tajn- 

 rill urn Cope. System.ntic Catalogue of the Eocene Vertebrata of New Mexico, 1875, p. 20. Re- 

 port U. S. Geol. Surv. W. of 100th Mer., Capt. G. M. Wheeler, iv. ii. p. 263, PI. Ixvi. iigs. 12-16. 



Plate LVI; figs. 1-2. 



This species was originally discovered in New Mexico by myself, but 

 it was Mr. Wortman who found its locality of greatest abundance, the Big 

 Horn basin of Northern Wyoming. 



The Systemodon tapirinus may be readily distinguished among the allied 

 forms by its superior dimensions, and by the large size of its premolar teeth. 

 The latter character implies an elongate muzzle, a feature also indicated by 



