Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 80. (Budapest 1988)

Pálfy, J.: Middle Triassic rhynchonellids from the Balaton Highland (Transdanubian Central Range, Hungary)

Remarks — "Rhynchonella Tommasii" was first described by BITTNER (1890) from the Southern Alps, but in the same volume he also described and figured a specimen from Köveskál and named it as "Rhynchonella decurtata var. vivida tumescens". In both description he mentioned the apparently great similarity of these two forms to each other and suggested the possibility of their belonging to the same species. DIENER (1920) already treated these forms together, keeping the specific name tommasii. This form really shows great resemblance to vivida. Diagnostic features for distinction are the less sharp lateral margin and the lack of the ventrally projected wings. GAETANI (1966) attributed this species to his new genus Decurtella, together with the already treated vivida. As it was seen, DAGYS (1974) moved vivida into his newly described genus Volirhynchia, but he did not mention tommasi in his fundamental work; neither did SIBLIK (1983) give a generic attribution of this species. Despite some open questions the present author thinks that the external and internal characters of tommasi are convincing enough to prove its belonging to the genus Volirhynchia. We have seen its great external similarity to vivida which is a certain representative of the genus Volirhynchia. Their internal features also fit more or less to each other. DAGYS determined their crura in the generic diagnosis as that of canalifer type, but it can be considered to be rather one of radulifer type. The figure of serial transverse sections of the type species Volirhynchia volitans seems not to contradict this judgement. Nevertheless, there are minor differences in the inner structure of Volirhynchia tommasi and V. vivida, as the former has a longer median septum and arched plates beside the dissimilarity of the dental plates. Distribution: So far Volirhynchia tommasi has been known from the Balaton Highland and the Southern Alps only, and seems to be confined to the Anisian. Volirhynchia projectifrons (BITTNER, 1890) (Plate 1 : figs 3-7, Fig. 6) 1890 Rhynchonella projectifrons sp. n. — BITTNER: p. 41, pi. 31 : figs 16-17. 1890 Rhynchonellaprotractifrons sp. n. — BITTNER: p. 41, pi. 31 : figs 19-22. 1895 Rhynchonella protractifrons BITTN. (partim) — SALOMON: p. 100, pi. 3: figs 19, 21-22 (non figs 16, 17, 18, 20, 23 and 24) Material: Altogether 5 well-preserved specimens, one from the Forrás Hill near Felsőörs, and 4 from the lower part of the Aszófő sequence. Dimensions: The following table shows the data measured on each specimens No. 1 originated from Felsőörs, Nos 2-5 are from Aszófő 1 2 3 4 5 Length 11.0 14.1 9.1 9.2 8.3 Width 11.0 16.8 9.1 10.0 8.8 Thickness 6.5 9.2 4.9 6.6 6.2 Description — External characters : Medium-sized to large shell in adult stage, oval in outline. Maximum width is at about the anterior third, maximum thickness is at about the half length in the juvenile stage, later shifting toward the anterior end. Biconvex form with a differently developed fold and sulcus on the adult specimens. In the very early stage of ontogeny a narrow sulcus developed on the brachial valve, of which a groove appears in the centre, probably representing a dorsal median septum. The lateral commissure arches gently ventrally to the point where it meets the uniplicate anterior commissure. The whole commissure is sharp and prominent. The height of fold grows during ontogeny. The fold is up to twice as wide as high. The anterior view of the fold varies from semicircular to almost rectangular (Fig. 6) The whole surface of both valves is smooth. Fig. 6. Drawing from the anterior view of three specimens of Volirhynchia projectifrons (BITTNER, 1890) from Aszófő, to show the variation in anterior commissure ; a = adult form, gently arched high fold (X2.5), b = juvenile form, gently arched low fold (x3) and c = juvenile form, moderatelyangular fold ( X 3)