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

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

Dimensions: The following table presents the data of six characteristic specimens : 1 2 3 4 5 6 Length 8.8 10.2 9.4 10.0 9.6 10.6 Width 9.9 10.7 10.1 11.2 11.1 12.5 Thickness 5.2 8.4 6.8 9.3 5.0 5.4 (Localities: 1 = Forrás Hill near Felsőörs; 2, 3, 4 — Aszófő; 5, 6 = Köveskál) Description — External characters : Small to medium-sized shell, characteristically triangular in outline. The angle between lateral margins is 70-80°, the anterior margin is slightly rounded in dorsal view. The shell is planato-convex to biconvex in lateral view, the brachial valve is slightly more convex, while the pedicle one is rather flat. The shell reaches its maximum width near the anterior end, the maximum thickness is placed at mid-length. The lateral commissure divides into two equal parts a flat, oval planarea. There is often a marked flattening at the anterior end of the shell. Sometimes the anterior commissure has a low uniplication. All the surface of the shell is costate. The sharp costation starts from the beak, 7 to 9 costae on each valve run straight to the anterior end without bifurcation, 2 or 3 of them are situated in the central fold. Their profile is trigonal in crosssection. The beak is high and erect. The pedicle opening is triangular in shape and hypothyridid. Internal characters (Fig. 2): Pedicle valve: Subparallel, dorsally slightly divergent and ventrally shorter, widely set dental plates separate the subquadrate delthyrial cavity from the semicircular umbonal cavities. The hinge teeth are strong, but not deeply projected into the sockets, the blu nt denticula are almost as well-developed as the hinge teeth themselves. Brachial valve : The hinge plates are almost horizontal. The socket is large and deep with p renounced socket ridges, of which the outer one is even markedly developed. The septalium is narr ow and shallow, supported by a short dorsal median septum. The crura are simple, first laterally, la ter dorso-venfrally elongated, trigonal shaped in cross-section. They are of radulifer type. Remarks —• Earlier several subspecies were distinguished within Decurtella decurtata. According to SIBLIK (1971a) the variety dalmatina and vivida are synonymous and must be considered as independent species. Their costation (blunt costae evolving during a later stage of growth) suggests their belonging to the genus Volirhynchia as DAGYS (1974) recognized it. The oxypterus variety of FRECH (1912) was based on a single brachial valve, so it is doubtful and still not justified by more recent data. BITTNER'S other variety, devota was thought by GAETANI (1969) to be another independent species, which has a diagnostically globose appearance and smaller, less curved beak. Such a form has not yet been recorded from the Balaton Highland. Another one of BITTNER'S variety, the mediana (BITTNER 1902) is thought by SIBLIK (1971a) to be a possible subspecies, since the smaller morphological differences does not allow one to create a new species for this form. Distribution: Decurtella decurtata is widely known from the Anisian, both from the Alpine and the German type facies and faunas. In Hungary it has been recorded from the Balat on Highland, the Aggtelek Mountains, and the Mecsek Mountains. The species seems to be confined to the Pelsonian. Genus Volirhynchia DAGYS, 1974 Volirhynchia vivida (BITTNER, 1890) (Plate 2: fig. 2; Figs 3-4) 1872 Rhynchonella altaplecta sp. n. (partim) — BÖCKH: p. 163, pl. 11 : fig. 29. 1890 Rhynchonella decurtata var. vivida sp. n. — BITTNER: p. 10, pi. 32: figs 11-12. 1890 Rhynchonella decurtata var. vivida excavata — BITTNER: p. 10, pi. 31: fig. 27. 1933 Rhynchonella decurtata var. divida (sic!) BITTNER — MILOSAVLJEVIC

: p. 212, pl. 1 : fig. 6. 1935 Rhynchonella decurtata var. vivida BITT. — MILOSAVLJEVIC : p. 270, pl. 1 : fig. 1. 1949 Rhynchonella vivida BITTNER — BESIC: p. Ill, pl. 1 : fig. 6. 1971 Decurtella vivida (BITTNER) — SIBLIK : p. 168, pi. 19; figs. 5-6, pi. 20: fig. 4, Figs . 3-4. 1975 Decurtella aff. vivida (BITTN.) — KOCHANOVÁ, MELLO et SIBLIK: pi. 7: fig. 5. Material: 6 well-preserved specimens from the Forrás Hill near Felsőörs and 2 incomplete specimens from Köveskál.