Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 15. 1992. (Budapest, 1992)

rounded. The anterior margin is straight or sligthly concave. The width is nearly equal to the length while the thickness is three-quarters of the length. The angle between the lateral margins is about 80°. Biconvex form, both valves are quite convex but the pedicle valve is more convex than the brachial one. The maximum width is situated at half of the length, the maximum convexity is at the posterior third. The beak is small and erect. There are two beak ridges on the pedicle valve running to half of the length. The lateral and the anterior commissures are straight. The shell surface is weakly capillate. The other characteristic form is triangular in outline. The sides of triangle are slightly convex, the base is slightly concave. The antero-lateral corners are rounded. The length is greater than the width while the thickness is half of the length. The angle between the lateral margins is about 70°. Biconvex form, both valves are equally convex. The maximum width is situated at the anterior margin, the maximum convexity is at the posterior third. The beak is small and erect. There are two well developed beak ridges on the pedicle valve, running to half of the length. The planareas are small, the lateral commissures run in the middle of them. The commissures are straight. Text-fig. 28 - Transverse serial sections of Zeilleria mutabilis