Shell small to medium (less than 15 mm long), profile medium to high, apex near center, aperture round to oval. All slopes straight to slightly convex. Sculpture of concentric growth lines, radial ribs sometimes present. Ground color typically white, pink, or red; unicolored or with darker radial rays or dots. Shell structure consists of only four layers. Outer layer complex prismatic forming a distinct border around aperture. Layer between border and myostracum [= muscle scar] wholly concentric crossed-lamellar. Myostracum typically faint. Inner shell layer radial crosscd-lamcllar, homogeneous under magnification. Lateral teeth roughly equal in size and shape and arranged in posteriorly diverging V shape. Marginal teeth absent. Basal plates relatively simple. Nuchal cavity gill absent; copulatory organ under right cephalic tentacle and secondary gill present in the subgenus Problacmaea Golikov and Kussakin, 1972.