The intestines of twenty ground squirrels (Citellus tridecemlineatus) were examined for protozoa. The following species of protozoa were found to be present: Giardia sp.?, Endamæba citelli, Chilomastix magna sp. nov., Trichomonas muris var. citelli, Trichomonas sp.?, Tetratrichomastix (Eutrichomastix) citelli sp. nov., and Hexamitus pulcher sp. nov. The first was found in the small intestine, all the others in the cœcum. In this paper all the above species except the first two are described, particular attention having been given to the morphology of the free Chilomastix magna and to its division phases. So far as is known, all these protozoa are commensals. Whether or not they assist in the digestion of cellulose, which is said to take place very largely in the cœca of certain animals, is unknown.