Potamolithus rushii is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Tateidae.

[1] Pilsbry's original text reads as follows:[1] Columella with a longitudinal groove or pit; outer lip with a strong varix.

of body whorl gibbous below suture; umbilical area moderate or large, bounded by a keel.

[2] There is some variation in the degree of depression of the whole shell, the amplitude of the columellar area and in the prominence of the hump on the back, which is sometimes almost suppressed.

[2] The two species are similar in general color-scheme, in the varix, absence of more rapid descent of the suture towards the mouth, etc., but are totally diverse in contour, the one being carinate, the other smooth and naticoid.

[2] They had the depressed contour of adults and were strongly carinate peripherally, but the carina is distinctly weaker in front of the mouth, apparently indicating that it begins when the shell has nearly two whorls and a diameter of about a millimeter.

[2] Very late in the neanic stage the basal keel appears, the shell then being about 5 mm in diameter; the columellar area is very narrow, at first linear.

[2] The marginal varix and the absence of any tendency of the last whorl to descend or loosen its coil anteriorly, show that this species is at its acme.