Shell thin-walled, with smooth surface, without crests and dimples. No sutural pores, all twenty plates connected by perfect sinuous sutures. Each plate with two elliptical aspinal pores, 2 to 5 times broader than numerous, roundish irregularly scattered coronal pores (30 to 50 on each plate). Radial spicules internal, not prolonged on outside of shell. Diameter of shell: 0.16 mm, aspinal pores: 0.01 mm, coronal pores: 0.002 to 0.005 mm.