Shell large, thin, both valves about equally convex, right valve more brilliantly colored; ears subequal, hinge line straight; beaks small, pointed,not prominent; orb of the shell somewhat oblique, anterior portion produced downward and forward, margin simple, entire, sharp; sculpture of wide little-elevated ribs, about seventeen in number, each with a central keel which is sharp and slightly serrate over two-thirds of the surface but becomes obsolete toward the margin; this keel is colored more deeply than the rest of the rib, and the color may be alternately concentrated at the prominences and fainter between them. In the specimens observed it is either deep rose color or a warm orange-brown, fading gradually on each side of the keel of the ribs, while the interspaces are pale or white, with faint narrow radiating lines of the color; on the right valve, except along the hinge line, the auricles are pale; the minute sculpture consists, on this valve, of fine radiating grooves, about a dozen between the carinae of each pair of ribs, across which are carried in fine scallops sharp little-elevated lamellae; these lamellae are easily felt, but visible only with some magnification; the left valve shows (in a rose-colored specimen) very little color, and that a mottled orange-brown confined chiefly to the ribs of the apical third; the ribs are keeled for a shorter distance than in the right valve, are generally fainter, while the microscopic sculpture is composed only of fine concentric incremental lines which have a silky appearance; the hinge line of the left valve slightly overrides that of the other valve and is serrate by fine transverse scales; the ears are subequal, the byssal notch shallow and rounded, without a pectinium; there are a few elevated radiating lines on these ears; internally the hinge line is nearly smooth, I he cartilage pit small and narrow, two short, stout auricular line radiate from it; the interior of the shell is white; the interspaces between the external ribs are defined by fourteen or fifteen pairs of elevated lira strongest distally and ending close to the margin. Maximum altitude of shell 60.0; maximum longitude 60.0; longitude of hinge line 25.0; diameter of closed valves 11.0mm.

Broadly fan-shaped, auricles subequal, compressed, thin-walled, left valve with broad, rose rays, right valve lighter colored or pure white, with ca. 17 radial ribs that are prickled near umbones, flattened near margins; interior white. Massachusetts to Florida, Gulf of Mexico. Length 30 mm (to 75 mm).