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Leptaena contermina
Taxonomy
Leptaena contermina was named by Cocks (1968) [= Strophomena rhomboidalis (Wilckens) Davidson 1871 pl. 39, fig. 17 only.]. Its type specimen is OUM C9168, a valve (pedicle valve), and it is a 3D body fossil. Its type locality is Hope Quarry, Minsterley, Shropshire, which is in an Aeronian marine mudstone in the Venusbank Formation of the United Kingdom.
Sister species lacking formal opinion data
Synonymy list
| Year | Name and author |
|---|---|
| 1968 | Leptaena contermina Cocks pp. 306 - 307 figs. PI. 6, figs. 8-13, PL 7, figs. 1-11 |
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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.
†Leptaena contermina Cocks 1968
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| L. R. M. Cocks 1968 | Transverse Leptaena with interior encircling ridges in both valves, and regular rugae.
Description. Exterior. Mucronate and sharply geniculate. Apart from the large ears, the shell shape is approximately semicircular, although rather transverse. Equally parvicostellate ornament, with ribs increasing slightly in size anteriorly. Occasionally new ribs arise either by intercalation or more commonly by bifurcating (OUM C9153 shows both methods on a single brachial valve, an external mould). Rugae regular and continuous. The number of rugae on the disc varies between six and ten within a population. The geniculation occurs at different lengths within a population, but usually between i-o and 1-4 cm. The angle between the disc and trail is between 75 and 90 degrees. Open delthyrium, prominent chilidium. The pedicle foramen has not been observed on any specimen. Pedicle interior. Teeth and dental plates small for the genus and fused to a small anterior extension of the hingeline. Large, prominent and evenly curving muscle boundary ridges, nearly meeting anteriorly and fusing posteriorly with an extension of the dental plates. A small median ridge divides the lanceolate adductor scars, which are usually very poorly impressed. In some specimens, the diductors completely enclose the adductors, in others they just fail to do so. Striae are developed on the muscle field, particularly on the diductors. The more coarsely pustulate disc and some of the trail are bounded by a nearly semicircular ridge which runs round the trail anteriorly but laterally crosses the geniculation and merges posteriorly with the hingeline at a low angle near the dental plates. The internal reflection of the ornament is much stronger outside this ridge. Coarse pseudopunctae posteromedianly, except on the muscle field, but not so prominent as in the brachial valve. Brachial interior. Cardinal process lobes prominent, between them a much smaller narrow blade-like process. Socket plates variably developed and widely divergent, with rarely-preserved striae on their anterior side. Running anteriorly and laterally is a three pronged platform which bounds the posterior edge of the adductor scars, and the middle prong of which divides them, forming a short, broad median ridge. This line is marked discontinuously anteriorly as a fine ridge until near the edge of the disc, and in many specimens is more pronounced near its anterior end. As with the ventral valve a ridge runs laterally from the hingeline posterior of the sockets to the edge of the disc, but instead of crossing the geniculation as with the pedicle valve, it stays on its edge, thus making a wall on the anterior edge of the brachial valve which is not reflected on the exterior. Except in the muscle field, there are prominent pseudopunctae which are random posteriorly, but anteriorlv are arranged in lines parallel to the external ornament. They are smaller and less well defined outside the encircling ridge. |