New Genux and tipecies of Marine Rodent. 



strongly convex, with one anterior and one posterior closed 

 loop, and one external and two internal lateral closed triangles. 

 Middle and last upper molars each with one anterior and one 

 posterior closed loop, and one lateral closed triangle on each 

 side (sometimes the lateral triangles are not quite closed in the 

 last tooth). The anterior loops of the second and third upper 

 molars are strongly pyriform, as in Phenacomys. 



First lower molar with anterior half bent strongly outward? 

 the anterior loop looking outward instead of forward. This 

 tooth has an anterior loop, a posterior loop, an external lateral 

 closed triangle, and two internal lateral triangles, the posterior 

 of which is closed. Second lower molar with one anterior and 

 one posterior closed transverse loop, and one lateral closed tri- 

 angle on each side ; last lower molar with an anterior oblique 

 closed loop, a posterior oblique closed loop, and a lateral closed 

 (or nearly closed) triangle on the outer side. (This tooth is 

 described more in detail in the generic diagnosis.) 



Haunts and Habits. Almost nothing is known of the life his- 

 tory of this interesting and heretofore unknown animal. Respect- 

 ing the specimens from Hacienda Magdalena Mr. Nelson writes : 

 " Not common. The two specimens obtained were caught, in 

 hollow trees." Another " was taken in the low dense woods near 

 the mouth of the Armeria River. They live in hollow trees." 



Measurements (taken in flesh] of Xenomys nelsoni. 



Type. 



