In the early spring of 1922 I was working with my friend Mr R. A. Staig at the rearing of larvæ and eggs of Stomoxys calcitrans in horse dung from a farm. Some of the manure had been left in the incubator (which was maintained at 24° C.) after all larvæ had been raised from it. On examining the surface of the material, which had been kept damp, it was found to be swarming with small Oligochætes and a rich culture of a testaceous Rhizopod (fig. 1). This latter is 35μ × 17μ in size, and appears to be identical with the organism figured by Leidy (10) as Trinema enchelys. It seems certain that Leidy had placed different species under this one name, and Cash and Waite (2) have placed in the species lineare those forms which differ from T. enchelys in being of smaller size and in having a test very thin and composed of ill-defined plates, which can hardly be seen in most of the specimens mounted in balsam. The present organism then can be placed in this species, Trinema lineare, Penard.