The youngest of the Chesapectens is the C. septenarius. It is different from older pectinidae in that it has a more symmetric hinge. It is smaller than most of its older cousins by about 30% (from about 2cm to 10cm) and quite flat.
The size of this shell is about 3cm in diameter.
The inner surfaces show clearly the hinge area and the muscle scars.

One can clearly see the deep right angle ridges characteristic of this species.

Front view

Side view