Valves strongly lunate with shallow mantle.
External valve surface with transverse ridges often terminating at dorsal and ventral valve margins in spine-like projections. Striae uniseriate or partially biseriate with small, rounded areolae.
Simple, short raphe present at both valve poles. Proximal raphe branches located near the valve/mantle junction, terminal fissures curving onto the valve face near the poles. Rimoportulae are absent.