CONUS

A genus consisting of species of Conus, having a rhomboidal or quadrilateral form and a coronated spire.

Shell conical, with very short spire, and narrow aperture with parallel borders; operculum unguiform Conus.

I suspect that Conus bullatus was meant, as the contrasting characters answer admirably.

The conus arteriosus too begins to be divided into two chambers, and in Protopterus this division is complete.

But when it dilateth itself it becometh rounder, the conus being drawn to the basis.