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)

and the majority of the Discohelix species preferred biotopes on submarin highs. On the other hand, D. orbis is rather common in basinal, deeper-water (ammonitico rosso) limestones, too. The high-numbered occurrences of this species presumably cannot be due to transportation, but rather to the fact, that this species lived (also) in deeper-water biotopes. It is suggested also by the observation, that the entire material was yielded by condensed, but autochtonous sediments of 2 to 3 cm thickness. Moreover, it is hard to realize a transportation selecting mainly the D. orbis specimens. On the other hand, it is difficult to decide that the occurrence in condensed limestones is produced whether by fossilization or environmental causes. Other fossil groups, e.g. ammonites and brachiopods do occur in crinoideal beds, and the brachiopods appear even in cherty rock-types, too. Accordingly, it is probable that the lack of D. orbis in cherty, crinoideal, or siliceous sponge-spicule-bearing limestones is caused by primary, paleoecological factor(s). Presumably the association with crinoids and sponges, or rather the detrital substrate formed from the skeletal parts of these latter, was the unfavourable circumstance. D. orbis, like the majority of the Jurassic gastropods (HALLAM 1972), would have preferred hard substrates. The studies on facies-dependence reinforce the results of WENDT (1968, p. 563) on the mode of life of Discohelix. Pentagonodiscus, which was suggested as more adapted for living in more agitated waters, occurs only in elevated biotopes. Additionally, their most common occurrences were submarine highs with tops presumably within the photic region of highly agitated watres. On the other hand, Discohelix species are common in deeper water Fig. 3. Stratigraphie distribution of the here described Discohelix and Pentagonodiscus species: 1 = D. cf. ornata, 2 — D. inornata, 3 = D. miocarinata, 4 = D. excavata, 5 = D. orbis, 6 = D. acarinata, 1 = P. initiopentagonatus, 8 = P. reussii.9 = ID. cotswoldiae, 10 = P. angustus