Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 75. (Budapest 1983)

Vörös, A.: Some new genera of Brachiopoda from the Mediterranean Jurassic

ing branches and double points, the transverse band is narrow. The muscle scars are very thin and subparallel posteriorly but at the middle of the valve they abruptly become large, spoon-shaped. At the posterior part the muscle scars are rimmed with sharp but not high ridges and there is a third, lower ridge (myophragm) between the scars. Discussion : The only genus closely connected with Lychnothyris is Hesperithyris also from the Tethyan Lower Jurassic. The two genera have the same external habit: gibbose. with big, incurved beak; they are similar internally too (with very peculiar spoon-shaped muscle-scars). The main difference is that Hesperithyris has strong, rounded ribs while Lychnothyris is completely smooth. Some multiplicate terebratulids described by DUBAR (1942) from Morocco (e.g. "Terebratula,, termieri, "T.„ costata) seem to be related also but they are not placed into valid (probably new) generic position yet. Fairly distinct from the Middle Jurassic multiplicate or partly smooth, rectimarginate genera (Plectothyris, Plectoidothyris, Parathyridina) the Hesperithyris - Lychnothyris group stands nearer to the Triassic Plectoconcha and can be ranged among the subfamily Plectoconchinae. Distribution : Pliensbachian of the Mediterranean Region (Sicily, Appennines, Southern Alps, Hungary). Family Pygopidae MUIR-WOOD. 1965 Subfamily Uncertain Genus Seeurithyris gen. n. Derivatio nominis: axe-shaped ; securis (Latin) = axe. Type species: S. adnethensis (SUESS. 1855) Diagnosis : Medium to large terebratulids, subtrigonal in outline, valves equally convex. Anterior commissure very wide, rectimarginate, ligate or gently sulcate. Cardinal extremities developed. Cardinal process large, crenulated. Hinge plates reduced or missing; crura emerging from inner socket ridges; loop short, narrow. Description : External characters (Figs. 13, 14) (Representative figures of the type species: HAAS 1884, pl. Ill, fig. 2a-c; PARONA 1885, pl. V, fig. 3-6; RENZ 1932, pl. II. fig. 2, 4): Seeurithyris consists of a few medium sized or large (up to 6 cm) terebratulids with subtrigonal outline and very expanded anterior margin. The shells are nearly equally convex but the convexity is variable within a single species, from very flat to almost globose. The anterior commissure is rectimarginate but tends to be ligate or gently sulcate in certain species. The hinge and the lateral margins meet at an obtuse angle forming elevated cardinal extremities. The shell surface is smooth with slight, irregularly spaced growth lines. The beak is erect to slightly incurved with blunt beak ridges. The foramen is mesothyridid and becomes displaced apically by resorption in adults (truncating the beak). A low ventral palintrope (interarea) is developed. Sometimes deep but poorly demarcated planareas could be seen in certain species. Internal characters (Fig. 6) — Pedicle valve: The pedicle collar is well-developed. The delthyrial cavity is subcircular. The hinge-teeth are moderately long, slightly expanded laterally. Denticula are well-developed, sharp. The ventral muscle scars are short, forming a horse-shoe shaped area. The mantle canal markings show four main trunks with several bifurcations (pinnate pattern) (Fig. 14). — Brachial valve: The cardinal process is wide, flattened, strongly crenulated and slightly extends to the delthyrial cavity. The hinge plates are reduced to narrow shelves on the sides of the inner socket ridges and sometimes they are missing. The inner socket ridges are strong and high, generally leaning over the sockets. The outer socket ridges are low and wide. The crura emerge from the inner socket ridges, sometimes with the insertion of very rudimentary hinge plates. The crural processes are low. slightly incurved. The loop is narrow and short with gently arched transverse band. The dorsal adductor muscle scars are slightly divergent, narrow and short. Species: S. adnethensis (SUESS) (1855, p. 31). —• S. paronai (CANAVARI) (1880, p. 18, pl. II, fig. lla-d). — S.filosa (CANAVARI) (1880, p. 20, pl. II, fig. 13a-d). — S. helenae (RENZ) (1932, p. 38, pl. II, fig. 6, 7) Discussion : Among Jurassic brachiopod genera Trigonithyris is the one showing strong external similarity to Seeurithyris. Internally, however, they are quite different: