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)

stratigraphical dating possible. The majority of the material came from the Upper Sinemurian and the Plienscbachian, but some Toarcian and numerous (approx. 250) Bajocian specimens are also available. This large and partly well-preserved material obviously needs treating. Taking into consideration that the research on Jurassic (especially Mediterranean) gastropods is relatively neglected, the results are expected to emerge from the scope of pure taxonomy. The present paper, the first part of a series, deals with the results of the systematic treating. To begin with the species of the family Euowphalidae is justified by the fact that this is the most commonly represented family in the Bakony Mountains Lower Jurassic: with approx. 150 specimens of 8 species. The Bajocian yielded only two species from a single locality. The specimens are deposited in the Paleontological Collection of the Hungarian Geological Survey, Budapest. Localities — The sedimentological study of the majority of the localities has been done by KONDA (1970). He distinguised four main facies types. The origin of these different facies types was studied by GALÁCZ & VÖRÖS (1972). On the basis of these latter studies, VÖRÖS (1974) evaluated the facies-dependence of the branchiopods (Fig. 2: A). The biostratigraphy of the profiles is given for the Lower Jurassic in GECZY'S (1971a-b, 1972a-b, 1974, 1975), for the Bajocian in GALÁCZ'S (1976) works, respectively. These studies make easier to characterize the localities shown in Fig. 1 and Table I. Morphological remarks Keels and last whorl — There is a few morphological element to detail after the exhaustive evaluation of WENDT (1968). As it is shown by the here described new species too, a feature of specific value would be the presence or lack of carinae on the keels. In all the investigated species, fine carinae of at least one or two whorl length appear on the embryonal shell. However, in Discohelix inornata sp. n. and D. acarinata sp. n. these carinae are lacking on the outer parts of the shell. From this point of view not only the vhole, but also a part of the teleoconch would be characteristic. Thus, in D. miocarinata sp. n. only the last whorl lacks the carinae. In several species the sculpture of the last whorl differs from that of the previous ones (D. excavata, D. miocarinata, ? D. cotswoldiae, etc.). In this way the shells show three distinct divisions: embryonal whorls (protoconch), juvenile whorls and last (adult) whorl appear. These three parts are connected by transitional portions. The observations suggests that the different sculpture of the last whorl endures temporally, thus enables specific characterization in itself. In spite of the limited specimen number and narrow stratigraphie extension, the designation of two of the here described new species (i.e. D. miocarinata and P. initiopentagonatus) can be supported by the above-mentioned morphological considerations. Parabolic sculptural elements and the growth of Pentagonodiscus angustus — The P. august us WENDT specimen shown in Plate II: fig. 9. makes the interpretation of the parabolic sculptural elements simpler (cf. WENDT 1968, pp. 555, 560). As it is clear from the figure, the "parabolic nodes" on the keels are actually the insertions of long, slit spines, similar to siphonal canals. These elements therefore do not indicate resorption, but rather changes in the direction of growth. The spines can brack off quite easily, but when are preserved, their delivery from the matrix needs exceptional fortune. Thus only their scars appear, together the infilled "notches". In connection with the spine-secretion, the direction of growth altered in the remaining part of the shell. The spiral threads incline to-