A description is presented of a new species of Subulura Molin, 1860, Subulura novomexicanus, collected from the spotted ground squirrel, Spermophilus spilosoma Bennett, 1833, in New Mexico. The males are 24 to 29 mm long, precloacal sucker 1.7–2.0 mm from posterior end, spicules subequal 0.83–1.0 long, and gubernaculum Y-shaped 0.21–0.39 mm long. Females are 34–39 mm long, vulva near middle of body 14.06–22.00 mm from anterior end, and eggs 0.04–0.05 mm long by 0.03–0.04 mm wide. The new species is distinguished from Subulura ungulatus Erickson, 1938 in being longer and having spicules that are distinctively different in size and form. It also differs from Subulura nevadense Babero, 1973 in being longer and having a larger egg size and smaller spicules. The new species is most similar to Subulura andersoni (Cobbold, 1876) (Thwaite, 1927); however, the males of this species are smaller and they have broad cervical alae, and the adults occur in squirrels of India. Reexamination of S. ungulatus showed 11 pairs of caudal papillae, including 4 pairs of preanals, 1 pair adanal and lateral, and 6 pairs of postanal papillae located at the end of the tail. Spermophilus richardsoni (Sabine, 1822) is a new host record for S. nevadense, and Montana is a new distributional record for this nematode. Eimeria callospermophili Henry, 1932, is a new record for S. spilosoma.