. La Canadian field-naturaliste. 168 Le Canadian Field-Naturalist Vol. 87 Gardenton). Le type de sol n'a pas semblé être un facteur majeur limitant la dispersion de l'espèce, puisque les individus ont été trouvés dans le sable et de till glaciaire ainsi que de sol limoneux. Les habitats humides ou boisés ont été évitées dans une plus large mesure par Geomys que par Thomomys. Dans toute son aire Geomys est typiquement un habitant de grandes graminées et mixte- grass prairie, et il est intéressant de trouver des abajoues le stockage souterrain et d'un spécimen capturé à partir de la chambre remplie de Gardenton stocks- racine du barbon (Andropogon gerardi

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. The Canadian field-naturalist. 168 The Canadian Field-Naturalist Vol. 87 Gardenton). Soil type did not appear to be a major factor limiting the dispersal of this species, since individuals were found in sand and glacial till as well as rich loam. Wet or wooded habitats were avoided to a greater degree by Geomys than by Thomomys. Throughout its range Geomys is typically an inhabitant of tall-grass and mixed- grass prairie, and it was interesting to find the cheek pouches and underground storage chamber of one specimen from Gardenton filled with root- stocks of big bluestem (Andropogon gerardii), a characteristic grass species of these communities. The majority of both species of pocket gophers in this area was limited to the edges of fields, road- ways, and railroad allowances, owing to extensive cultivation and the presence of aspen-oak forest and marsh in the east. Geomys was very abundant in certain fields, particularly those planted with alfalfa, and one farmer reported trapping at least 100 gophers along the edge of his property over several years. During spring flooding he noticed their movement (through the appearance of new mounds) from the saturated fields to the higher roadbanks. As Soper (1944) remarked, the mounds of the plains and those of the northern pocket gophers are indistinguishable. The tunnels of Geomys are generally of greater diameter, which is under- standable considering its larger body and claw size (Figure 2). Thomomys had not previously been found in this region east of the Red River, so we were greatly surprised when this species appeared in many traps where Geomys was expected. In the vicinity of Emerson, where Geomys had been re- ported over 50 years ago, Thomomys was now very abundant, even in lawns. Further specimens of Thomomys were taken west of Dominion City and Stuartburn, and south of Gardenton. The ranges of the two species are parapatric, within a mile of each other at five localities. In fact, the Manitoba population of Geom

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