Arcidens confragosus shell description:

“Shell rhomboid, inflated, subsolid, or solid, slightly inequilateral; beaks high and full, their sculpture consisting of irregular, doubly-looped ridges, the bases of the loops being developed into strong, pinched-up nodules, which extend out on to the disk of the shell; in front of and behind the loops there are a number of radiating, wavy, subnodulous lirae or small ridges; from the anterior row of knobs extending backwards and downwards there is a series of strong folds and these are crossed by wrinkled, radiating, sometimes zigzagged, threads; the posterior slope has radial, wrinkled sculpture, while the anterior base has usually merely concentric striae; posterior ridge rather high; post-dorsal region almost winged; epidermis brownish-green with dark bands, sometimes clouded; left valve with an arched, somewhat elongated tooth under the beak, which often curves upward; in front of this there is a compressed tooth; right valve with a strong, subcompressed tooth in front of the beak; at the beak the hinge plate is cut away for the reception of the tooth in the left valve; laterals reduced to blurred, uneven vestiges; beak cavities deep; muscle scars shallow; nacre bluish-white, dull, often with uneven radial sculpture, with a wide prismatic border” (Simpson, 2014; Mather, 2007).