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

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

Systematic description Order RHYNCHONELLIDA KUHN. 1949 Superfamily Rhynchonellacea GRAY, 1848 Family Wellerellidae LIKHAREV, 1956 Subfamily Cirpinae AGER, 1965 Genus Lokutella gen. n. Derivatio nominis: after the name of the village Lókút (Bakony Mts., Hungary). Type species: L. palmaeformis (HAAS, 1912) Diagnosis : Small to medium sized rhynchonellids, trigonal in outline, valves nearly equally convex. No fold or sulcus, anterior commissure straight but forming a wide sinus. Planareas well-developed. Costae few, usually strong. Beak small, erect to slightly incurved. Median septum long but low. Hinge plates fused, forming a septalium or muscle trough. Crura prefalcifer. Description : External characters (Representative figures of the type species : HAAS 1912, pl. XIX, figs 2-4; BENIGNI 1978, pi. 15, figs la-e): Lokutella consists of a few species of small to medium sized rhynchonellids with trigonal or "axiniform" outline. The brachial valve is a little more convex than the pedicle one, which sometimes can be almost flat in lateral view. A very faint posteromedial trough suggests an early sulcate stage; otherwise there is no perceptible fold or sulcus. The planareas are well developed, generally concave. The bordering beak ridges are sharp in the brachial valve while rounded in the pedicle one. The lateral commissures run in the deepest line of the planareas but tend to reach the beak ridges of the brachial valve. From these extreme points the whole anterior commissure is deflected ventrally, forming a wide, low sinus. The ornamentation consists of a few to more than a dozen, usually strong, ribs which sometimes change in number by fusion or splitting toward the anterior margin. The beak is small, slightly incurved. The deltidial plates have been observed only in serial sections: they are short and disjunct. Internal characters (Figs 1, 2) — Pedicle valve: The delthyrial cavity is subquadrate with ventral groove(s); the umbonal cavities are elongate trigonal in cross section. The strong dental plates are parallel but seem to be divergent in incorrectly oriented specimens (see: Fig. 1). No pedicle collar has been observed. The deltidial plates are simple, disjunct. The hinge-teeth are straight, expanded dorsally, crenulated. Denticula are well developed. — Brachial valve (Fig. 10): There is no cardinal process. The fused inner hinge plates form a shallow, V-shaped septalium or muscle trough supported by a rudimentary, long but low, median septum. (These characters show considerable variation according to orientation: e.g. the somewhat tilted specimen on Fig. 1 displays a flat septalium and a well-developed median septum.) Outer hinge plates are massive, horizontal. Inner and outer socket ridges are well developed. The crural bases emerge dorsally and give rise to crura of '"prefalcifer" type. Species: L. cuneiformis (CANAVARI) (1883, p. 103, pl. XI, fig. la-d) (non MANSUY, 1912). — L. Hasina (PRTNCIPI) (1910, p. 81, pl. Ill, fig. 7a-d). —• L. deangelisi (PRINCIPI) (1910, p. 78, pl. Ill, fig. 5a-d, 6a-d). — L. palmaeformis (HAAS) (1912. p. 232, pl. XIX, fig. 2a-d, 3, 4). — L. kondai sp. n. Discussion : Lokutella belongs to the large group of Liassic rhynchonellids with trigonal, "axiniform" appearance, coarse ribs and planareas, especially abundant in the Mediterranean region. This group was provisionally included by AGER (1956-67) into the genus Prioiiorhynchia. Now it seems that several members of this "axiniform" assemblage could belong to different stocks, for example "P." palmata (OPPEL, 1861) and "P." desori (HAAS, 1884) can be assigned to Cuneirhynchia because of their general form and the position of their lateral commissures. Lokutella stands nearer to Prioiiorhynchia; their internal features are not markedly dilferent. The external differences are distinctive: Lokutella has fewer ribs and characteristic, sometimes laterally expanded, trigonal outline; it is rectimarginate or has a wide, low sinus, while Prioiiorhynchia is more or less uniplicate. The most important difference lies in the form and position of the lateral commissures: straight and vertical in Prioiiorhynchia while bent and displaced dorsally in Lokutella. An other genus of the family Wellerellidae, Trigoiiirhyiichella from the Upper Triassic stands nearer to Lokutella in form having a similar, trigonal outline and is here regarded as a possible ancestor