Sowerbyella

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Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000):

• Concavoconvex profile; parvicostellate to unequally parvicostellate ornament; small arched pseudodeltidium; no chilidium; short teeth; no denticles on hinge line; short but widely diverging dental plates; bilobed ventral muscle field open anteriorly, with posterolateral muscle-bounding ridges; thin short ventral median septum posteriorly; small cardinal process; wide flaring socket plates; bema variable, usually present but occasionally absent; median septum in dorsal valve variably developed, usually absent; similar to Anisopleurella but with prominent pair of ventral side septa, which sometimes form edge of bema and are sometimes developed above it.

Cocks & Rong (1989):

• Diagnosis: Bema variable, sometimes absent. No denticles on hinge line. Median septum in brachial (dorsal) valve variably developed, usually absent. Like Anisopleurella but with prominent pair of central side septa, which sometimes form the edge of the bema and are sometimes developed above it.
• Remarks: Rõõmusoks (1959) separated a subgenus Viruella based on ornamentation (like Eoplectodonta), the presence of a median septum in the brachial (dorsal) valve, and a raised muscle platform in the brachial (dorsal) valve. However, those three characters show great variation, and in fact all are present in the type species of Sowerbyella sericea, apart from the ornamental difference, which we regard as of specific, not generic importance.
• See Cocks & Rong, 1989 for a list of assigned species

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