trochoid

From Ancient Greek τροχοειδής (trokhoeidḗs), from τροχός (trokhós, “wheel”) + εἶδος (eîdos, “form, image”).

trochoid (plural trochoids)

1. (geometry) The curve traced by a point on a circle as it rolls along a straight line
2. (malacology) An organism or fossil with a trochoid shell (especially one in the gastropod family Trochidae), or the shell itself.

trochoid (comparative more trochoid, superlative most trochoid)

1. Capable of rolling.
2. Allowing rotation.
3. (malacology, of a shell or fossil) High-spired; conical.
   

   Bartsch's star bolma has a trochoid shell.