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)

Measurements: D H S H/D H/S A U Plate I: fig. 10 14.6 6.6 3.8 0.45 1.74 248° 131° Material — Thirteen specimens, all with preserved test, but more or less damaged. Diagnosis — Spire concave, only the keels of embryonal shell are carinate, the shellsculpture comprises transversal bars. Shape — Dextral discoidal form, with a spire less concave than the umbilicus. The whorlsurface is convex on the outer, but flat on the spiral and umbilical sides. The keels are rounded and uncarinate both on the juvenile and adult whorls. On the available fragmentary peristomes no modification is visible. Sculpture —Spiral sculpture is visible only on the outer side, with magnification. It comprises random fragments of spiral threads. The spiral and umbilical sides are covered by periodically appearing roof-tile-like, tiny transverse bars, which fade on the outer side immediately after the keels. The bars are divided into extremely fine growth-lines, which give rise to the transverse sculpture on the outer side, where these are stronger. Embryonal shape and sculpture — The embryonal whorls are raised in the beginning (i.e. on the nucleus and a whorl). On each keel of the second and third whorls a fine carina appears, which becomes smooth before the onset of the adult sculpture on the fourth whorl. Except the carinae, the embryonal shell is free of sculpture. Remarks — The best peserved specimen shown under magnification a peculiar sculptural pattern. From periodically repeated, spot-like depressions along the suture, arise tangencially directed, prorsiradiate, fine, virgatotom and slightly opisthocyrt bundles of lines, which reach the keels. The origin of these lines is problematic. Perhaps these are traces of a former organic outer layer. On the basis of uncarinate keels after the embryonal whorls in D. acarinata, this species is easily distingusihed from the similarly sized D. miocarinata with carination up to the penultimate whorl, and D. excavata with carination throughout he shell. The similarly uncarinate D. inornata differs in its sculpture and dimensions. Probably the forms regarded by G. G. GEMMELLARO (1874) as D. excavata are conspecific. His Plate 9: figs. 14-15. show well the characteristic bars of the sculpture, and the size is also similar. The cross-section on his fig. 16. clearly shows that the keels are rounded throughout the shell. It is clear from the description, that GEMMELLARO also observed the differences from the D. excavata. Distribution — Western Sicily, „Pygope aspasia zone" ? ; Bakony Mountains : Kericser, beds with mixed Obtusum to Ibex fauna — Davoei Zone; Közöskúti-árok, Ibex Zone and a bed with mixed Ibex Zone to Lower Toarcian fauna. ? Discohelix cotswoldiae (LYCETT, 1850) (Plate II: figs. 1-3; Fig. 6f) 1968: Discohelix (Discohelix) cotswoldiae (LYCETT, 1850) — Wendt, p. 572., pi. 110., figs. 5-12.,. text-figs. 2F, 3M. Measurements: D H S H/D H/S A U Plate II : figs. 1-2 22.1 7.3 4.6 0.33 1.59 — 143° Plate II: fig. 3 22.7 6.7 4.6 0.29 ^ 1.45 220° 140° Material — Twenty, mostly damaged and a few excellently preserved specimens. Shape — Dextral, discoidal, nearly bilaterally symmetrical forms. The keels are distinct throughout the shell, and except the last 1 to 1.5 whorl, bear weak carinae. The peristome tapers out slightly, the outer and somewhat the inner lip is thickened. Sculpture — The adult sculpture appears simultaneously with the disappearing of the embryonal ornamentation. The adult sculpture comprises of regularly repeated small ribs. These ribs begin as corrugations of the keels, but later elongate transversally. With a gradual weakening, the ribs end before reaching the suture, and do not spread to the outer side. On the penultimate whorl the riblets fade out gradually, thus the last whorl is smooth. Some low ridges are visible sometimes mainly near to the peristome. On the penultimate whorl, together with the fading of the transverse riblets, the spiral lines, which cease after the embryonal shell, reappear on the spiral and umbilical sides. On the basis of the sculpture of a juvenile specimen, this happens quite earlier on the outer side.