160 Merriam New Genus and Species of Murine Rodent. 



beads like Nyctamys, large lachrymals, a large interparietal, and 

 large and greatly inflated audital bullie, which differ from those 

 of an} 7 murine with which I am acquainted and resemble those 

 of some of the carnivores. In dentition it combines the o-rooted 

 upper molars of the true murines with the non-tubercular pris- 

 matic grinding crowns of the arvicolines, and has the broadly 

 rounded alternating closed triangles of Phenacomys, only even 

 more crowded. 



The new genus may be characterized as follows : 



Xenomys * gen. nov. 



Skull resembling that of Neotoma in general form and appear- 

 ance, but differing in possessing marked elevated and laterally 

 projecting supraorbital beads, much larger and heavier lach- 

 rymals, greatly enlarged and inflated audital bull<T, which are 

 elongated antero-posteriorly and parallel to the axis of the skull 

 and to each other, instead of being set obliquely as in Xcotoma 

 (in which genus they would meet in the middle of the pterygoid 

 fossa if produced forward along their strongly convergent axes). 

 The anterior border of the squamosal above the zygomatic pro- 

 cess is marked by a projecting vertical ridge corresponding to 

 the postorbital process of Cunictilm, Myodes, and Phenacomys, and 

 serving to indicate the separation of the (small) temporal from 

 the (large) orbital fossa. Posteriorly the squamosal does not 

 reach the occiput as it does in Neotoma, but ends about half- way 

 between the posterior root of the zygoma and the occiput, Its 

 posterior spicule reaches the mastoid. The paroccipital pro- 

 cesses are long and stout. The interparietal is very large and 

 somewhat diamond-shaped. The condyloid process of the mandi- 

 ble is long and slender and higher than the coronoid process. 



Dental Characters. Molars truly rooted ; the roots closed at the 

 tips ; upper molars 3-rooted ; lower molars 2-rooted. First upper 

 molar with anterior and posterior roots subcylindric and a broad 

 flat root in the middle on the inner side, the latter slightly 

 notched at the tip and having the appearance of two roots grown 

 together. Between the middle and posterior root in the speci- 

 men examined is a small needle-like auxiliary or supplemental 

 root about half the length of the others ; middle upper molar 

 with 2 anterior and 1 posterior roots, the anterior on the inner 

 side about double the size of the others ; last upper molar with 



* Xenomys: from 5''-""*, ntningo, and />-'V, mouse. 



