According to Visher (1914:88), mountain sheep formerly inhabited all the areas of buttes in Harding County but were extirpated in the 1890's. Sheep Mountain, a large butte just below the south end of the Slim Buttes, was reported to be the last area in which these animals occurred. Over and Churchill (1945:54) mentioned both the Cave Hills and Slim Buttes as localities formerly inhabited by _O. c. auduboni_. Early in 1961, the South Dakota Game Commission introduced 12 animals, four rams and eight ewes, from Alberta (subspecies _O. c. canadensis_) on the Slim Buttes, but none is known to have survived to 1968. SPECIES OF UNVERIFIED OCCURRENCE The ten species of mammals listed below are not known certainly to occur in Harding County, but there is a strong likelihood that some will be found in the area or once occurred there. Three were mentioned by Visher (1914) as having been seen or taken in the county at the time of, or prior to, his biological survey of 1910 and 1912, but his accounts were not supported by adequate documentation. In addition to the kinds listed, several other mammals, such as Keen's bat (_Myotis keenii septentrionalis_), the red bat (_Lasiurus borealis borealis_), or the least weasel (_Mustela nivalis campestris_) are known to occur near enough to the area that the possibility of their presence cannot be discounted. ~Sorex cinereus haydeni~ Baird, 1858.--No shrews presently are known from Harding County. This species almost certainly will be found in relatively mesic habitats there, however, as our field parties have taken specimens in adjacent Bowman County, North Dakota, and only a few miles to the west of the county in the Long Pines Hills of Montana. ~Sorex merriami merriami~ Dobson, 1890.--This shrew inhabits somewhat more xeric areas than most other members of the genus and surely occurs in northwestern South Dakota. Specimens are on record from western North Dakota and northwestern Nebraska, and in the summer of 1970 a field party from The University of Kansas took one but a half mile west of the Harding County (state) line in Carter County, Montana. ~Spermophilus richardsonii richardsonii~ (Sabine, 1822).--Visher (1914:88) reported that he saw individuals of this species "in the extreme northwestern corner" of Harding County. However, the limits of the presently known range of the species are approximately 150 miles distant from that area.