Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 73. (Budapest 1981)
Vörös, A.: A survey of the Rhaetian (Upper Triassic) Bivalvia from Borzavár (Bakony Mts., Hungary)
Genus PLAGIOSTOMA SOWERBY, 1814 Plagiostoma cf. praecursor QUENSTEDT, 1856 (Plate II : 4) * 1856 : Plagiostoma praecursor — QUENSTEDT, Der Jura, p. 29, pl. I, fig. 22-24. 1859: Lima praecursor QUENST.— WINKLER, Schichten der Avicula..., p. 8, pl. I, fig. 5. 1861 : Lima praecursor. — MOORE, Avicula contorta Zone, p. 500, pl. XV, fig. 9. 71861: Lima punctata Sow. —STOPPANI, Couches à Avicula..., (pars), p. 73, pi. 13, fig. 3. (non fig. 1-2, 4-6.) 1861 : Lima discus STOPP. — Ibid., p. 73, pl. 13, fig. 7. 1861 : Lima acuta STOPP. — Ibid., p. 74, pl. 13, fig. 9. 1866: Lima praecursor, QUENST.—CAPELLINI, Infralias. Spezia, p. 72, pl. VI. fig. 8. 71870: Lima praecursor QUENST.? — FISCHER-OOSTER, Thun, p. 76, pl. Ill, fig. 4. 1891 : Radula (Plagiostoma) praecursor QUENSTEDT sp. —• SIMONELLI, Cetona, p. 634, pl. I, fig. 13. M a t e r i a 1 : 3 internal casts with shell fragments. — Locality : Borzavár, Rhaetian grey limestones. D i m e n s i o n s (mm): length: 27.0 18.2 height: 24.5 16.3 apical angle: 100° 88° Description : The shell is of small size for the genus; strongly inflated. The outline is a little oblique, subcircular. The margins are evenly convex, except the anterodorsal part which is nearly straight. The umbo is prominent and lies in the posterior one-third of the total length. Only the posterior auricle is visible but even it is fragmentary. The shell surface is ornamented with a great number of fine radial ribs which are a little wavy and flat-topped. The interspaces are narrower than the ribs and bear very fine punctures. Remarks : STOPPANI (I.e.) described a series of forms under different names which seem to be closely allied to P. praecursor. One specimen of his P.punctatum (I.e., pi. 13., fig. 3.) is included into the present synonymy after DESIO (1929, p. 89.). The P. discus and P. acutum are very similar to P.praecursor even on the basis of STOPPANI'S figures; they were regarded as synonymous by DITTMAR (1864, p. 160.). This interpretation is accepted here, in spite of the opposite opinion of DESIO (1929, p. 88-89.). P. praecursor and P. punctatum Sow, (in STOPPANI'S sense) seem to be connected with transitions but their relation is not cleared up until now. Distribution : Rhaetian of the British Isles, South Germany, the Northern and the Southern Alps, the Central Apennines and the Bakony Mts. (Hungary). Plagiostoma sp., aff. fischeri (TERQUEM, 1855) (Plate II: 5) Material : an internal cast with shell fragments. —• Locality : Borzavár, Rhaetian grey limestone. Dimensions (mm): length: 16.5 — height: 15.7 Description : The shell is of small size for the genus; moderately inflated. The outline is slightly oblique, subcircular. The anterodorsal margin is nearly straight, the others are equally convex. The umbo lies at about the posterior one-third of the total length. The posterior auricle is fragmented but was presumably small and pointed. The remains of the shell do not show any radial ornamentation ; the growth lines are hardly visible. Remarks : The species P. fischeri (TERQUEM) is known from the well illustrated descriptions by TERQUEM (1855, p.318, pl.XXII, fig.5a-b) and STOPPANI (1865, p. 207, pi. 35, fig.20). Its most important features are the very large size and the almost total absence of the radial ornamentation. The specimen from Borza vár is too small to be regarded as conspecific with P. fischeri, but the smooth appearence suggests an obvious affinity between them.
