It is made available, with a full generic description, in Blainville's article "Mollusques" of "Dictionnaire des Sciences Naturelles" vol.

The first formal fixation for this genus was by Deshayes (1830) in the entry for Thracia of "Dictionnaire classique d'histoire naturelle" vol.

The hinge has upon each valve a horizontal and narrow nympheal callosity, which sometimes expands into a spoon-shaped projection, and contains an internal ligament, which is prolonged, and slightly issues outwardly into the corselet.

[2] The animal is oval, thick, enveloped in a very delicate mantle, diaphanous upon its sides, through which is distinctly seen the branchiae and the abdominal mass.

The two others are seen at the posterior part, and give passage to two distinct tubes or tracheae, cylindrical, fleshy, approaching each other towards their origin.

These tracheae can be drawn into the portion of the mantle which surrounds them, the covering of which is loose, and gives this part the appearance of a vulva.

The abdominal mass is voluminous, and is terminated by a small, oval foot, compressed, fringed in the form of a crest, and sub-anterior.

The retracting muscle of the trachea of the right side has an oval form, and is continued upon the abdomen by becoming thin and uniting with the mantle.

That of the left side is of an irregular, oval form, and adheres by its internal surface to a membranous, elastic fold which arises from the internal opening of the large trachea, enlarging as it continues, and terminates by a semicircle which exceeds by many lines[clarification needed] the retractor muscle of that trachea.