RODENTIA MURINAE NEOTOMA MEXICAXA. 



491 



yellowish tinge. The hairs ahove and on the sides, as well as those on the middle of the helly, 

 are pltimheous at base. The tail is dusky above, whitish beneath. 



The skull of this species offers striking points of distinction, from both N. floridana and 

 micropus, though most closely resembling the latter. The upper outline of the skull is slightly 

 convex, less so than in these other species. The nose is longer than N. micropus, the incisive 

 foramina larger ; the zygomata further separated than in N. floridana, but more nearly parallel 

 than in N. micropus. The upper surface of the head is strongly concave, longitudinally, the 

 temporal crests well marked. The nasal bones and the slender nasal postero-superior process 

 of the intermaxillary end on the same line posteriorly, and do not extend as far backwards as 

 the anterior extremity of the orbits, while in the others the intermaxillary processes extend 

 considerably backwards of this ; the nasal bones, too, are broader at their middle point than in 

 the others. The rami of the lower jaw are higher than in any other species examined ; the 

 neck of the condyloid process elongated, its axis forming an angle of fully forty-five degrees 

 with the base ; the highest point of the condyle is even higher than the coronoid process, instead 

 of being considerably below its level. The lower part of the post-coronoid notch is acute, the 

 coronoid process smaller than usual ; the notch behind the condyloid process is very long. 

 When the lower jaw is placed on a horizontal surface, a perpendicular at the posterior extremity 

 will be tangent to this and the posterior extremity of the condyle, instead of falling consider 

 ably in advance of it as in other species. The body of the bone in advance of the molars is 

 less deep than usual. The lower molars are narrow and quite parallel, the lobes narrower, and 

 their sides more parallel. 



I do not feel sure, however, that all Ihese peculiarities of the skull will be found characteristic 

 of the species, as individual specimens sometimes vary considerably. 





The specimen collected by Dr. Webb was captured in October, 1852, at Chevate, near Ojo. 

 Caliente, on the road between El Paso and Chihuahua, about one hundred miles from the latter 

 place. Their curious structures were seen in various directions between the rocks, and consisted 



