_Comparison._--From _Scalopus aquaticus_, of which ten subspecies have been seen including those of significant geographic position, _S. montanus_ differs in: Skull slenderer, less angular and relatively narrower across mastoidal region; cranium arched with hind part flattened; external pterygoid region less expanded; teeth relatively small, especially last upper molar. From _S. inflatus_, known to me from Jackson's description (N. Amer. Fauna, 38:53-54, pls. 2, 3, September 30, 1915), _S. montanus_ differs in: Skull less angular and slenderer, prelachrymal region not inflated; zygomata slenderer. _Remarks._--_S. montanus_ is known from a single specimen, which represents the second known occurrence of the genus _Scalopus_ in Mexico. The other occurrence is that of _S. inflatus_ in the state of Tamaulipas. _S. montanus_ is geographically isolated in mountainous country from other species of _Scalopus_. Ten of the recognized subspecies of _S. aquaticus_ were available for examination and descriptions of others were studied. It was found that the number and magnitude of the differences separating any one of these subspecies from an adjoining one was less than those separating _S. montanus_ from _S. a. texanus_ and _S. a. intermedius_, which are, geographically, closest to _S. montanus_. _S. montanus_ seems not to be closely related to _S. inflatus_ of Tamaulipas. _S. montanus_ is given specific rank because of the great degree of difference between it and its nearest relatives, and because of its geographically isolated position. The specimen of _S. montanus_ was taken in a tunnel found by digging away a mound thought to be that of the pocket gopher, _Thomomys sturgisi_. A trap set in one direction in the tunnel caught the mole; a trap set in the other direction in the tunnel was later covered with soil, evidently by a gopher. After the capture a thorough inspection of the area revealed no "raised" tunnels, typical of _Scalopus_. A series of _Thomomys_ was taken in this area in sets placed in tunnels found under similar mounds. This locality was near the headquarters of the Club Sierra del Carmen in a parklike stand of oak timber in a cañon, at an elevation of 4950 ft. as recorded by our altimeter. The plant association was judged to be characteristic of the Upper Sonoran Life-zone, not far below the beginning of the Transition Life-zone. The area was heavily grazed by goats, hogs and horses and had little grass or other ground cover under the trees. The soil in this cañon was not deep and consisted of a rocky, marly mixture, pale red in color, evidently produced by weathering of the reddish volcanic rocks bordering the cañon.