Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 59. (Budapest 1967)

Pintér, L.: A revision of the genus Carychium O. F. Müller, 1774, in Hungary (Mollusca, Basommatophora)

ANNALES HISTORICO-NATURALES MUSEI NATIONALIS HUNGARICI Tomus 59. PARS ZOOLOGICA 1967. A Revision of the Genus Carychium 0. F. Müller, 1774, in Hungary (Mollusca, Basommatophora) By L. PINTÉR, Budapest There is nothing much said about the genus Carychium in Hungarian malacological literature. The various authors had not deemed it worth while to discuss it at length, because the sole Hungarian species belonging to it, minimum O.F. MÜLLER, 1774, seemed to be rather uniform and hardly liable to vary. True, a variation, Carychium minimum ssp. tridentatum (Risso,) 1826, has long been listed in our fauna, but the difficulties involved in its separation, and the highly relative value of the identification, were not worth the trouble. Perhaps this very relativeness gave birth to the mistrust in treating Carychium tridentatum (Risso) —a distinct and "good species" in foreign literature since long decades — as a taxon anything more than of a subspeeifie rank in our home publications. According to the traditional means of identification, the most characteristical features of the two species (or subspecies) are the proportion of the total height (H

x

) and width (W), and the total height (Hj) and apertural height (H

2

) respectively. Literature carries, in general, the following figures : Carychium minimum O. F. MÜLL. H

X

:W = 1.6 — 2 : 1 Hi:H

2 = 2.3-2.55 : 1 Carychium tridentatum (Risso) H

1

:W = 2.1 — 2.4 : 1 H

x

:H

2 = 2.55-3 : 1 In this respect, the data of the authors rather agree with each other. Accordingly, the investigated specimen is to be regarded as Carychium minimum in which the proportion (P

x

) of H, and W does not exceed 2, and that of P

2 ^HjiHj) is below 2.55. The figures for Carychium tridentatum are above 2.1 and 2.55 respectively. Theoretically, the difficulty would lie in the actual existence of the proportion between 2 and 2.1. Whoever has actually tried, even once, to separate the two species, will know from his own experience that the majority of identifications are insecure owing to an overlap, in most of the cases, of the proportions. In essence, there will always remain in any given population a rather high per cent of individuals which might be relegated, on the basis of the two kinds of proportions, to any one of the two groups. WATSON and VERDCOURT (1953) published a paper on the occurrence of Carychium species in Great Britain. After a thorough study, the two authors have shown that, for a taxonomic separation of the species belonging to the genus Carychium, there is but one reliable specific feature, namely the shape and position of the parietal lamella (Figs. 1, 2). This feature proved to be of such constancy that, on its basis, the specific distinctness of Carychium tridentatum (Risso) can be established with complete certainty. The Figure clearly illustrates the difference between the two species. If the penultimate whorl over the aperture is carefully removed, the parietal lamella, extending upwards, will become easily discernible. In the case of Carychium minimum O. F. MÜLLER, the configuration of the lamella resembles an obtusely pointed acute angle of uniformly arcuate sides toward the aperture, whereas, in Carychium tridentatum (Risso), it tends initially horizontally, indeed, frequently upwards, and then sweeps steeply and almost