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

Internal characters (Text-fig. 28): The dental plates are thin, straight and divergent. The delthyrial cavity is trapezoidal in cross-section. The umbonal cavities are relatively large and rounded in cross-section. No pedicle collar has been observed. The hinge plates are thin and there is a deep septalium. The socket is deep and not crenulated. The teeth are straight and slightly crenulated. There is no denticulum on its side. The teeth strongly diverge from the dental plates. The median septum runs to 2/5 of the length. Most of the loop is missing. Remarks: Extremely variable form. The subpentagonal end member is similar to Zeilleria alpina but the antero-lateral corners are less rounded. The outline of Z. alpina is almost circular and the curvature of beak is smaller. On the basis of these features, Canavari's (1883) specimen is probably a Z. alpina. The subtriangular form is similar to Z. choffati but differs in the convexity of valves and the location of the maximum width and the maximum convexity. Distribution: According to Aimeras (1964), Z. mutabilis is Sinemurian to Pliensbachian in age. According to Vörös (1982), this species occurs in the Upper Sinemurian and the Pliensbachian of the Bakony Mountains. The species was reported from the Eastern Alps (Hierlatz), the Southern Alps (South Tyrol, Sospirolo, Piemonte), the Northern Appennines (Monte Pisano), the Western Carpathians, the Gerecse Mountains and the Bakony Mountains. Zeilleria alpina (GEYER, 1889) (Pl. V, Fig. 2; Text-figs. 29-30) 1883 Waldheimia mutabilis OPPEL - Canavari: p. 92, pi. 10, figs. 9-10. 1889 Waldheimia alpina n.sp. - Geyer: p. 29, pi. 3, figs. 33-3«. 1943 Waldheimia alpina GEYER - Vígh: p. 28, pl. 1, fig. 4. 1960 Zeilleria alpina GEYER - Fülöp et al.: p. 17, pl. 1, fig. 3. Material: 34 complete specimens. Dimensions (mm): Specimen M.91.28. (Text-fig. 29) length: 13.1, width: 12.3, thickness: 7.2. Description - External characters: Small to medium-sized shell, subcircular in outline. The width is nearly equal to the length while the thickness is about half of the length. The Text-fig. 29 - Drawing of angle between the lateral margins is about Zeilleria alpina 120°. Biconvex form, the convexity of valves are equal. The maximum width is situated at half of the length while the maximum convexity is at the posterior third. The beak is small and erect. There are two poorly developed beak ridges on the pedicle valve, running to one-third of the length. The lateral and the anterior margins are straight. The shell surface is weakly capillate. Internal characters (Text-fig. 30): The dental plates are parallel. The delthyrial cavity is rectangular in cross-section. The umbonal cavities are relatively large and rounded in cross-section. No pedicle collar has been observed. The hinge plates