Comprehensive Description

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General Description

The shell is stout with a subcircular-trigonal outline. The valve height/ length ratio is 0.84, and the width/ length ratio is 0.25. The periostracum was absent. The sculpture consists of growth lines and weak irregular concentric ridges. The escutcheon is shallow and is limited by a sharp ridge. The lunule is indistinct, moderately broad, short, and is limited by fine striae. The valves are inequilateral with the umbones positioned 41% of the shell length form the anterior margin. The umbones are slightly prosogyrate. The anterior dorsal margin is straight, sloping to a broadly rounded edge with the anterior margin, while the posterior dorsal margin is very slightly convex, sloping to a blunt angle with the posterior margin. The anterior and posterior margins are slightly rounded-truncated and have an evenly convex transition into the ventral margin. The ventral margin is slightly convex. The pallial line is distinct and slightly impressed over its entire length, and is rather widely distant from the shell margin. The anterior adductor scar is drop-formed and evenly impressed. The anterior pedal retractor scar is a very small, irregular oval that is deeply impressed and fused with the anterior adductor scar. The posterior adductor scar is a slightly impressed, irregular subquadrangular shape that is fused to the small posterior pedal retractor scar that lies immediately below the end of the posterior dorsal margin. The inner margin of the valve bears 1-2 shallow concentric grooves. The nymph is strong, rather broad and deeply sunken, with a sloping posterior end, occupying 28% of the valve length. A fibrous layer of ligament is 78% of the posterior lamellar layer.

Dentition of the right valve: The ventral cardinal (1) is strong, wedge-shaped, and radiates obliquely anteriorwards. The 3a ramus is very short, thin, and is parallel to the anterodorsal margin. It is fused in its proximal part with the anterior edge of the 3b ramus. The 3b ramus is narrow, bifurcated and radiates obliquely posterior ventralwards.

Dentition of the left valve: The 2a ramus is thin and is subparallel to the anterior dorsal shell margin. It is fused in its proximal part with the proximal part of the 2b ramus. The 2b ramus is stout, broad and triangular, radiating obliquely posterior-ventrally. The 4b tooth is short, thin and is subparallel to the posterior dorsal shell margin.

(Krylova & Janssen, 2006).


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