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Strophomenata - Strophomenida - Leptellinidae
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|G. A. Cooper 1956||Shell small for the genus, wider than long with the width at the hinge varying from about 1.5 to 2 times the length. Cardinal extremities acutely angular, auriculate to submucronate. Lateral margins sloping inward ; anterior margin broadly to narrowly rounded. Surface beautifully ornamented by costellae of different sizes and fine concentric fila. Costellae of three sizes, the larger ones appearing in three generations, a median costella stronger and wider than the rest usually marks the center of the pedicle valve. Umbonal region usually marked by 3primary costellae on each side of the median one. Costellae of intermediate size intercalated in 2 generations as the shell grows so that an adult has about 8 of the primary and intermediate costellae in a space of 5 mm. at the front margin. Spaces between larger costellae occupied by about 4 very fine costellae that are cancellated by crowded concentric fila. Oblique wrinkles, often of considerable length, mark the shell just anterior to the posterior margin.
Pedicle valve nearly flat in lateral profile ; very slightly convex in the posterior half but flattened in the anterior portion. Umbo narrow, slightly swollen ; beak small and protruding slightly posterior to the posterior margin. Anterolateral region flanking depressed anterior part thrown into a slight broad fold. Cardinal extremities somewhat flattened. Interarea short and flat; apsacline to nearly procline ; pseudodeltidium narrow and strongly convex.
Brachial valve only partially known from the exterior. Umbonal region concave. In order to fit the interior of the pedicle valve the brachial valve must be slightly convex in the anterior region.
Interior of pedicle valve with a moderately deep delthyrial cavity well filled at the posterior by callus. Valve well thickened just inside the periphery, this thickened portion of the interior giving the resupinate profile to the species. Muscle field large, occupying most of the visceral region. Adjustors located at the base of the dental plates as usual ; diductor scars long and slender, generally with a low ridge running the length of the middle of the scar. Adductor impressions large. Pallial sinuses deeply impressed. Teeth double ; dental plates stout, giving off ridges that bound the exterior of the muscle field.
Brachial valve with cardinal process typical of the genus.
|A. Williams 1962||Transversely semi-elliptical and auriculate Palaeostrophomena about one-half as long as wide, with a wide median fold in the brachial valve giving the gently concavo-convex shells a resupinate appearance, and ornamented by 8-12 costellae per millimetre antero-medianly and 4-6 pairs of strong rugae with a wave-length of less than 1 mm. disposed postero-laterally at an oblique angle to the hinge line; ventral vascula media initially parallel, branching at about one-third the length of the pedicle valve.|