Original Description: "Testa aequivalvi inauri cuneata, plicis senis obtusis." {fide Linnaeus, 1771)

Additional Description: Shell thin, inequilateral and somewhat translucent; right valve slightly more convex than left; both valves carry 5 to 10 primary ribs, and are sometimes flanked by secondary riblets. Auricles unequal. Color variable from cream, to reddish brown and to almost purple, with white markings or dots.
Size: Normal adult size range is 40 to 60 mm.

AS Pseudamusium septemradiatum:
Description. - Shell thin, subtranslucent. Valves inequilateral, right valve slightly more convex than left one. Left valve fold into 7-8 primary ribs, carrying 1-3 stronger riblets; secondary ribs might be present in between the primary ribs, without more pronounced riblets. Right valve 7-8 ribs, incised in middle, giving impression each rib formed out of two fused ones. Anterior auricles 1.23-1.26 times as large as posterior ones. Anterior auricle right valve 5-6 obscure ribs,left valve 3-4 obscure ribs. Posterior auricle right valve 5-6 ribs, left valve 4-6 obscure ribs. Microsculpture consisting of very fine radiating riblets. Top angle varying from 107°-109°. Colour generally red, but white, cream and purple specimens have been examined also. Colour pattern left valve consisting of basal colour (generally red) with white or cream markings and fine dots; right valve white with (generally red) markins near the top.
Dimensions. - Largest specimen examined approximally 62 mm height x 62 mm width x 12 mm depth. Distribution. - From the Arctic region of the eastern Atlantic to northwest Africa. The species is also found in the Mediterranean.
Habitat. - Living on silty bottoms at depths varying from 10 - 600 m. In the Mediterranean it lives at distinctly larger depths than in the northern part of its distribution.
Remarks. - Specimens from the northern part of its distribution can reach considerable dimensions and have often a pattern of dots and streaks on the valves. Specimens examined from Morocco and the Mediterranean are more or less uniformy coloured and not exceeding 40 mm.
Locard's Pecten amphicyrtus refers most probably to Pseudamussium septemradiatum, as to the 7 ribs and red colour described. During my visit to the Museum National d'Histoire Naturelle, Paris I have not found this species in the type collection. Later Bavay mentions this species also, his figured specimens from unknown locality and Madeira being Flexopecten flexuosus, his specimen from Pouliguen being a worn P. septem radiatum.

Found along the eastern Atlantic Ocean from Norway to Morocco, including the western Mediterranean Sea.
Habitat: Littoral zone to deep water, on muddy or muddy sand bottoms.