Bailey (1915:102) referred a specimen from Crow Buttes to _T. t. bullatus_, but Swenk (1941:3), in the original description of _T. t. pierreicolus_, suggested that this same specimen "probably" was referable to the latter because he assumed it came from soils of the Pierre series. However, Baker (1952:8) included the Crow Buttes in the Hell Creek formation and, in any event, one of us (Jones) examined the specimen in question and found it clearly referable to the subspecies _bullatus_. Over and Churchill (1945:32) erroneously assigned pocket gophers from northwestern South Dakota to two different subspecies (_bullatus_ and _clusius_), referring at least one individual from Harding County to _T. t. clusius_. Fleas, _Dactylopsylla ignota_ (Baker), were found on one individual examined. Molting adults were taken in each month from May through August. ~Perognathus fasciatus fasciatus~ Wied-Neuwied, 1839 Olive-backed Pocket Mouse _Specimens examined_ (16).--2 mi. N, 5 mi. W Ludlow, 3; 4 mi. S, 7 mi. W Ladner, 9; 10 mi. S, 5 mi. W Reva, 1; 14 mi. S, 4 mi. W Reva, 2; 15 mi. S, 4 mi. W Reva, 1. This pocket mouse is not uncommon in areas of short grass and sage in Harding County. None of five adult females taken late in June was pregnant or lactating, but three had enlarged mammae indicative of reproductive activity earlier in the spring, to which young of various sizes in our series also attest. Active molt was evident on adults taken on June 19, 26, and 28. Our specimens are intergrades between _Perognathus fasciatus fasciatus_ and the paler _P. f. olivaceogriseus_. Average external measurements of seven adults (two males and five females) are: total length, 138.0 (130-150); length of tail, 65.3 (59-74); length of hind foot, 17.1 (15-18.5); length of ear (six specimens only), 6.8 (6-7); weight in grams (five specimens only), 12.9 (11.2-14.6). Selected cranial measurements of the two males and two of the females are, respectively, as follows: occipitonasal length, 24.0, 23.2, 23.5, 22.3; interorbital breadth, 4.9, 5.2, 5.0, 5.0; mastoid breadth, 13.0, 13.1, 12.2, 11.9; length of maxillary toothrow, 3.3, 3.3, 3.1, 3.4. ~Perognathus hispidus paradoxus~ Merriam, 1889 Hispid Pocket Mouse An adult female, not reproductively active, that was trapped in rather sparsely vegetated rangeland to the southwest of Slim Buttes (14 mi. S and 4 mi. W Reva) on July 19, 1961, is the only specimen of the hispid pocket mouse on record from Harding County. Other species of small mammals taken in the same or adjacent traplines were _Perognathus fasciatus_, _Dipodomys ordii_, _Reithrodontomys megalotis_, _Peromyscus maniculatus_, and _Onychomys leucogaster_. A single individual reported from Wade, Grant Co., North Dakota, by Bailey (1927:123), approximately 100 miles to the northeast, is the only specimen known from a more northerly locality. ~Dipodomys ordii terrosus~ Hoffmester, 1942 Ord's Kangaroo Rat