(Described as
Risella) The depressed shell is trochiform, with flattened
whorls and a keeled periphery. The shell is not umbilicated. The
aperture is rhomboidal, marked with brown inside the margin. The
operculum is paucispiral. These shells are distinguished from
Trochus, which they resemble in form and sculpture, by their non-nacreous interior. The animal is distinguished by eyes on the tentacles instead of on peduncles, and by the absence of the lateral membranes of the foot. ==Species==