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

(Original description) Shell is moderately large, biconic-fusiform, imperforate, slightly turreted, with a very broad smooth shoulder, spirally striated below it.

[2] Sculpture : The indistinctly turreted whorls have a broad shoulder showing deeply curved growth-lines.

Below the faint angle there are short axial costae which are very little raised and broadly convex, about 10 on a whorl.

The shell contains six whorls without the protoconch, first slowly then more rapidly descending, angled at the lower third, the broad shoulder slightly concave.