F. B. Loomis — Wasatch and Wind River Rodents. 129 



as was described and attributed to Plesiarctomys delicatior 

 Leidy by Cope.* 



The species is characterized by its considerable size, the 

 plump marginal cusps, and large interior basin. The two 

 anterior cusps are united by a paralophid ridge, in front of 

 which is the beginning of a cingulum or anterior marginal 

 ridge. The two rear cusps are connected by a posterior mar- 

 ginal ridge. The mesostyle is very small. On molar 3 the 

 posterior margin is considerably widened. From P. delica- 

 tior this species is distinguished by the general slenderer build, 



Fig. 5. Paramys major, x 4 ; lower jaw of the left side. 



especially in the cusps being less plump, the interior basin 

 larger, and the mesostylid less developed. The lower molar 

 series measures 16J mm . 



Paramys excavatus sp. nov. 



Type No. 327, a lower jaw of the right side from the Wind 

 River beds on Briclger Creek near Lost Cabin, Wyo. 



This delicate species is distinguished by its slender jaw and 

 low crowned teeth with tiny marginal cusps. The interior 

 basin is large and fairly deep. The anterior cusps are not 

 united by a marginal ridge, though from the protoconid two 

 tiny ridges rise and start inward, soon however fading out. 



Fig. 6. Paramys excavatus, x 4 ; lower jaw of the right side. 



The two posterior cusps are connected by a marginal ridge 

 which on the last moiar is a wide inrolling buttress. This last 

 molar is distinguished from other species by the rear being 

 notched medianly. The mesostylid is tiny. The incisors are 

 rather wide, a broken face measuring 3-J mm deep by 2 mm wide. 

 The length of the lower molariform series is 12 mm . 



* Ibid., vol. iii, 1884, pi. 24a, fig. 11-13. 



