Lacking ventral and dorsal side ribs, bi-lobate fins, with developed posterior footlobe curving over contracted fins. Pigmented area surrounding mouth. Somewhat oval embryonic shell, not pointed, and separated by distinct constriction. Lateral ribs only developed in anterior three-fourths part of shell. Whole ventral side of posterior footlobe provided with unicellular glands, crowding at anterior margin. Left mantle corner provided with a balancer. [van der Spoel, 1967]
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