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

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

tion. Their profile is trigonal in cross-section. The beak is relatively high, suberect to erect. The pedicle opening is hypothyridid. Internal characters (Fig. 7) : Pedicle valve : The delthyrial cavity is subquadrate. The dental plates are widely set, and after a subparallel stage become slightly dorsally divergent and ventrally shorter. The umbonal cavities are semioval. A pedicle collar has not been observed. The hinge teeth as well as the denticula are well-developed, not expanded dorsally. Brachial valve: The ventrally arched hinge plates become flatter beyond the plane of articulation. The inner and the outer socket ridges are well-developed, the sockets are wide and shallow. The moderate septalium is V-shaped. The septalial plates are connected with the dorsal median septum, which anteriorly suddenly decreases and disappears through a short ridge-like phase. The crura are of prefalcifer type, originating from the the median part of the hinge plates, ventrally arched and V-shaped in cross-section. Remarks — The studied specimen agreed well with those known from previous descriptions and figures. The diagnostic features are clear enough for a certain identification. As regards generic attribution, DAGYS' view is accepted here (DAGYS 1974, 1977). Distribution: Costirhynchopsis mentzeli is known from both the Alpine and the Germantype Middle Triassic, from the Pelsonian and the Illyrian. First it was described from the German Muschelkalk, but beside the Balaton Highland it was also found in the Southern Alps, the Dinarids and the West Carpathians. Subfamily Praecyclothyridinae MAKRIDIN, 1964 Genus Caucasorhynchia DAGYS, 1963 Caucasorhynchia altaplecta (BÖCKH, 1872) (Plate 3: figs 1-4; Figs 8-11) 1872 Rhynchonella altaplecta sp. n. — BÖCKH: p. 163, t. 11: fig. 28 (non fig. 29 = Volirhynchia vividä) 1890 Rhynchonella alteplecta BOECKH — BITTNER: p. 11, pi. 37: figs 9-15. 1906 Rhynchonella altaplecta BKH. — ARTHABER: pi. 35: fig. 10. 71914 Rhynchonella alteplecta BÖCKH — SMITH: p. 146, pi. 94: figs 15-16. 1971 Caucasorhynchia altaplecta (BOECKH) — SIBLIK: p. 180, pi. 20: fig. 5. 1978 Caucasorhynchia aff. altaplecta (BÖCKH) — LEIN et SIBLIK: p. 217, pl. 31 : fig. 6, Fig. 6. Material: 284 specimens from the Forrás Hill near Felsőörs and 1 specimen from Köveskál. Mostly well preserved but silicified shells. Dimensions: The scatter diagrams of the figures 8 and 9 show the dimensions of 25 measured specimens and that of the holotype in addition. Description — External characters : Medium-sized shell, subtrigonal or subpentagonal in outline. Maximum width is located near the anterior third, maximum thickness at half length. Both valves are equally convex. The angle between the lateral margins may vary between 75° and 105°, but most often it is about 90°. The posterior part of the lateral margin is straight, but becomes curved ventrally toward the antero-lateral corner. Around its posterior part a marked, wide, flat or deepened planarea is developed. The anterior margin is uniplicate. The fold is wide and its height greatly varies. The development of the sulcus on the pedicle valve starts from its posterior third. The posterior part of the shell is smooth as well as the lateral flanks except for a blunt edge which runs from the beak toward the antero-lateral corner on the brachial valve. There is a similar one bordering the sinus on the pedicle valve. There are costae on the fold which have a rounded trigonal profile. They evolve from the posterior third of the shell. The number of costae is 2 to 6, rarely bifurcation were also ascertained. The beak is small, hardly exceeding over the brachial umbo, and suberect. The pedicle opening is submesothyridid. Internal characters (Fig. 10) : Pedicle valve: The delthyrial cavity is subquadrate. The dental plates are moderately widely placed, parallel to subparallel, and ventrally shorter. The umbonal cavities are narrow. The hinge teeth are straight and stout. Brachial valve: The horizontal hinge plates are flat and fused. The sockets are relatively deep, bordered by the well developed inner and outer socket ridges. The septalium is very reduced. The