Clavus formosus is a species of sea snail, a marine gastropod mollusk in the family Drilliidae.
The shell is pyramidal in form, with the upper part of the whorls distinctly concave. The surface is closely tuberculate-plicate at the middle. The aperture is small. The ground colour is white, ornamented with large conspicuous tessellated reddish-brown spots.
Its description is almost identical to Clavus laeta (Hinds, 1843)
The type locality is Capul Island in the Philippines. It has subsequently been reported from other parts of the tropical western Pacific, specifically in the demersal zone of the Red Sea. and off Papua New Guinea.
In his Monograph of the genus Pleurotoma, Reeve inadvertently applied the name Pleurotoma tessellata to two different species. In the errata to the work, he corrected the name of Species 331 to Pleurotoma formosa, which therefore constitutes the valid original description of the present species. The name Pleurotoma tessellata was retained for a different taxon described earlier in the same monograph (Species 244).
Subsequent revisions placed Pleurotoma formosa in the genus Clavus.