Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 71. (Budapest 1979)

Szabó, J.: Lower and Middle Jurassic Gastropods from the Bakony Mountains (Hungary). Part I.: Euomphalidae (Archaeogastropoda)

From the earlier illustrations, that of STOLICZKA 1861. pi. 3., fig. 13. is different, having a tetragonal outline. Disregarding this case, other earlier works made this characteristic species easily distinguishable. Distribution — Eastern Alps, Hierlatz limestone; Eastern Sicily, „Terebratula aspasia zone"; Bakony Mountains: Sümeg, ? Upper Sinemurian; Kericser, beds with mixed Obtusum to Ibex Zone faunas; Közöskúti-árok, Ibex Zone. Pentagonodiscus initiopentagonatus sp. n. (Plate II: figs. 6-7; Eig. 6h) Holotypus: Plate II: fig. 6. — Locus typicus: Lókút, Kericser — Stratum typicum: Hierlatz limestone — Derivatio nominis: pentagonal in the beginning; the initial part of the teleoconch shows pentagonal shape. Measurements: D H S H/D H/S A U Plate II : figs. 6-7 20.0 9.8 6.8 0.49 1.44 218° — Material — The available specimen shows the preserved juvenile and the majority of the outer whorls. Diagnosis — Dextral form with concave spire, only the juvenile whorls show pentagonal shape, sculpture with fine spiral lines, dense ribbing in the spiral and umbilical sides and nodes of two kind of strengh in the keels. Shape — Dextral, discoidal form with less concave spiral than umbilical side. The juvenile whorls are pentagonal in outline, but on the last two whorls the normal logarithmical coiling of the embryonal shell renews. However, the arrangement of the sculpture on the last two whorls retains the pentagonal symmetry. The keels are distinct and carinate throughout the shell. The surface of the whorls is flat on the spiral and umbilical sides, and convex on the outer side. Peristome and inner structure of the shell is unknown. Sculpture — From the third whorl the spiral lines are visible on the whorl-surface. From the penultimate whorl onwards, these lines are arranged into pairs. The pairs are 3 to 4 times widely spaced than space between them. On the spiral and umbilical sides 6 of these paired lines appear. The outer side is covered by dense, evenly-spaced lineation. Contemporaneously with the spiral lines, tiny transverse ribs appear strengthening slightly toward the keels. On the penultimate whorl the endings of these riblets strengthen into nodes. The nodes become increasingly stronger and sparser. On the last whorl the nodes appear independently from the riblets; there are stronger nodes at intervals of 35 to 36°, and three smaller, similar nodes between them. Within a space between two stonger nodes 13 to 17 riblets are visible. The nodes are elongated transversally, and fade out rapidly in the two, especially in the outward direction. The stronger nodes appear in points corresponding to the "tips" and the side bisectors of the former pentagonal whorls, thus the earlier pentagonal symmetry is retained. Embryonal shape and sculpture — The coiling of the embryonal whorls (approx. two and half) follows normal logaritmic spiral, with a nucleus slightly elevated on the spiral side. Because of the strong recrystallization, the sculpture cannot be studied here, only some uncertain portions of spiral lines are visible. Remarks — The juvenile (approx. 6) whorls of P. initiopentagonatus resemble those of P. reussii. The difference, on the basis of this limited material, is the stronger sculpture, the stronger divergence from the normal spiral coiling and the smaller whorl-width in P. reussii. The diameter of the pentagonal whorls in P. initiopentagonatus is 8 mm. In a diameter bigger than this, a distinction from P. réussi seens to be more certain. After this stage the specific features of P. initiopentagonatus are present: i.e. the loss of the pentagonal shape, the apparence of a different sculpture. In P. reussii the habit of the shell remains unchanged up to the adult stage (12 to 15 mm in diameter). Distribution — Bakony Mountains: Kericser, Davoei Zone. Pentagonodiscus angustus (WENDT, 1968) (Plate II: figs. 8-11; Fig. 6i) 1968: Discohelix (Pentagonodiscus) angusta WENDT-WENDT, p. 573., pi. 110, figs. 17-21., text-figs. IB., 2H., 30., 4A-B., 6A-B. Measurements: D H S H/D H/S A U Plate II: fig. 8 17.5 5.1 4.7 0,29 1.06 — Material — Ten specimens, some are excellently preserved.