Zemacies torticostata is an extinct species of sea snail, a marine gastropod mollusk in the family Borsoniidae.

The whorls show eighteen radial ridges, which extend from suture to suture and are strongly twisted forward at the anterior end.

A series of very fine spiral striae cover all parts of the whorls.

The aperture is not preserved in any of the specimens, but the fairly distinct growth lines show that the anal notch was broad and rounded.

[2] This extinct marine species is endemic to New Zealand and was found in Middle Eocene strata.