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

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

median septum is ridge-like and rather short. Pronounced crural bases appear near the distal ends of the hinge plates. The crura are of radulifer type. Variability — As the scatter diagrams of the length, width and thickness show (Figs 8-9), Caucasorhynchia altaplecta has a characteristic morphological variability. (The spots form a cluster rather than fit to a definite line.) Beside this the most important differing features are the costation and the character of the uniplication. Fig. 11. shows the number of costae in 20 specimens. In onefourth of these specimens studied a branching costa also occurred. The profile of costae ranges from the extremely rounded to the almost sharp. Remarks — As it was already pointed out concerning Volirhynchia vivida, only one of the two figures of the original description of BÖCKH showed this species. BITTNER found the forms with three costae to be the most characteristic, but also mentioned specimens with four or five costae turning up more rarely. SIBLIK (1971b) differentiated a new subspecies, Caucasorhynchia altaplecta acuticostaia which has diagnostically more numerous, sharper, and more often branching costae. He retained the nominate subspecies for the morphotype known from the Balaton Highland. Based on the present studies this distinction is justified. It should be noted, that in our material only Caucasorhynchia altaplecta altaplecta was found. Distribution: Beside the Balaton Highland this species is known from the Anisian formations of the Eastern Alps, Southern Alps, Dinarids and West Carpathians. Subfamily Holcorhynchellinae DAGYS, 1974 Genus Holcorhynchella DAGYS, 1974 Holcorhynchella delicatuia (BITTNER, 1890) (Plate 2: fig. 3; Fig. 12) 1890 Rhynchonella delicatuia sp. n. — BITTNER: p. 11, pi. 35: figs 28-29. Material: One well-preserved specimen from Aszófő. Dimensions: Length 6.8 mm, width 6.2 mm thickness 3.9 mm. Description — External characters: Small shell, subpentagonal in outline. The pedicle valve is strongly convex, semiglobose, while the brachial valve is flattened after an early biconvex stage of the shell growth. So the appearance in the lateral view is rather planato-convex. Maximum width and maximum thickness are located at about mid-length. The lateral commissure runs straightforward anteriorly. The brachial valve holds a sulcus along its whole length. This sulcus is narrow, groove-like near the umbo and gradually broadening on the anterior half. Near the anterior end a secondary fold is developed within the sulcus giving an intraplicate appearance to the anterior commisure (Fig. 12). The whole surface of the shell is smooth. The beak is characteristically triangular in dorsal view, medium-sized and suberect. The pedicle foramen is hypothyridid. Internal characters: The internal character remains unknown, because only a single specimen of this species was found, so there was no possibility for serial sectioning. Remarks : This specimen agrees well with those figured by BITTNER (1890), which also originate from the Balaton Highland, from the locality Csicsó. — There are several closely related forms mainly described by BITTNER (1902) from the Dinarids, which can be distinguished by the different plication. According to DAGYS (1974) these forms are very probably congeneric, though no evidence for their internal characters has been found as yet. Distribution: The Holcorhynchella delicatuia was found in the Balaton Highland and so far seems to be confined to the Balatonicus Zone (Pelsonian).