Cope.] lo4: j-j^ec. 16, 



Mr. Wortman from the Big-Horn. From these I learn that the dental 

 system is different from that characterizing the species of Hyracotherium. 

 There is no diastema posterior to tlie superior canine, wliile in the latter 

 genus there are two. Anterior to the canine there is a considerable one 

 in the Hyracotherium. This part is not preserved in any of the specimens 

 of S. tapirinum. The characters mentioned have induced me to separate 

 the latter as type of a distinct genus, Systemodon. An examination of the 

 figures and descriptions given by Dr. Lemoine of his PachynolopJms 

 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. craspedotum of 

 the Wind River country, with which it agrees in size. 



Systemodon semihians, sp. nov. 



This species was also abundant in the Big-Horn region, jaws and teetli 

 of sixteen individuals having been obtained. Its dimensions are a little 

 smaller than those of the S. tapiri?ms, especially as to the premolar teeth. 

 There is also a short postcanine diastema, which is not seen in the S. 

 tapirinus. 



The proportions of the maxillary series are represented hj a left max- 

 illary and premaxillary bone, with all the teeth in place, but the crowns 

 lost from the first premolar anteriorly. The crowns of the true molars are 

 somewhat worn, so I confine the description of these to the premolars. 

 The third and fourth have considerable transverse extent, the latter being 

 wider than long. The second has scarcely any internal tubercle, but 

 only a low postero-internal heel. The internal tubercle of this tooth 

 is large in S. tapirinus. The crown has two cusps, the posterior lower. 

 The last two premolars have two external cusps close together. They 

 have also an anterior external cingular lobe, as in the true molars. 

 There is a posterior external basal lobe in the third premolar, but none 

 or a rudiment on the fourth. No internal cingulum on the premolars. 

 The superior true molars, although worn, show' a prominent anterior 

 external basal lobe, and no complete internal cingulum The base of the 

 crown of the first premolar is narrow antero-posteriorly, and it has two 

 roots as in 8. tapirinus. It is in close contact with the second premolar, 

 and is separated from the base of the canine by a space a little less than 

 its own anteroposterior diameter, and less than the diameter of the 

 canine. The base of the crown of the latter shows that it is not a large 

 tooth, and has a wide lenticular section. The base of the external incisor 

 is rather large, and is compressed. 



Measurements of superior teeth.. ]\L 



Total length of superior series 0720 



"molar " 0310 



" " "premolar " 0250 



Diameters base of canine \ anteroposterior 0055 



t transverse 0040 



