Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 79. (Budapest 1987)

Conti, M. A. ; Szabó, J.: Comparison of Bajocian gastropod faunas from the Bakony Mts. (Hungary) and Umbria (Italy)

ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 79. Budapest, 1987 p. 43-59. Comparison of Bajocian gastropod faunas from the Bakony Mts. (Hungary) and Umbria (Italy) by M. A. CONTI, Roma & J. SZABÓ, Budapest M. A. CONTI & J. SZABÓ: Comparison of Bajocian gastropod faunas from the Bakony Mts. (Hungary) and Umbria (Italy). — Annls hist.-nat. Mus. natn. hung. 1987 79: 43-59. Abstract — The systematic part of this paper, containing also nomenclatorical and additional taxonomic remarks to the species common in both faunas, resulted a revised joint list of the Bakony Mountains and the Umbrian faunas (Table I). Designation of a new genus is also given here: Laevitomaria (Pleurotomariidae

). Table 1 informs about the mode of life of all the 98 species, recognised in the two areas. Palaeoecologic circumstances of the localities and the palaeo/bio/geography of the two Tethyan regions are also discussed. With 2 figures and 1 table. Introduction — During the last decade, after an interval of almost a century, several papers were published more or less contemporaneously on the Bajocian gastropod faunas of the Tethys (SZABÓ 1979, 1980 a, b, 1981,1982, 1983; CONTI & FISCHER 1981, 1983 1984 a, b) from the Bakony Mountains as well as from Umbria. In these papers, numerous new taxa were established. Many of them became subjective synonyms and this fact caused confusions in the taxonomy. For this reason the authors thought necessary to give a complete revision of the faunas. Comparing the Italian and Hungarian material, further species, in bad state of perservation, became identifiable. The corrected faunal lists (Table 1) show clearer picture of relationship between the gastropod faunas of the two regions of the central Tethys. Generally, the writers followed the systematics proposed by Cox (in MOORE 1960) as in their previous works. In case of certain groups, however, this systematics seemed to be rather artificial and needed a basic revision. In this paper, some genera are revised completely in respect of familiar position. Necessarily, this means partial revision of some families, too. Systematics — During the preparation of this paper, an important methodological problem emerged: what is the significance of the presence or absence of an umbilicus (disregarding pseudoumbilicus) in classification? This feature was not used consistently by former palaeontologists. It was regarded to have importance either on generic or on species level, respectively. Usually in a featureless group (like Crossostomatidae), it was attributed a generic role but in some other families (for example: Pleurotomariidae) having a lot of morphological characters, the existence or lack of an umbilicus got only specific value. Unfortunately, no biological evidence has been given to explain why an umbilicus appears and why not. The two opinions are as follows: 1. The most useful features for classification are the ones which may be characterized by "yes-no" pairs. The presence or absence of an umbilicus belong to these criteria. Without knowing their real taxonomical importance, it is useful to make subdivisions at generic level in featureless families. 2. The anomphalous stage is only one in the scale (0- < 300°), along which the umbilicus Annls hist.-nat. Mus. natn. hung., 79,1987