Flag Pen Shell (Atrina vexillum)

Max length : 48.0 cm.
Shell reaching a very large size, thick and solid, inflated, variable in shape from triangular to hatchet-shaped or subglobular. Dorsal margin usually nearly straight, posterior margin broadly oval to somewhat truncate in outline. Ventral margin broadly convex posteriorly and concave near the umbones, often strongly lobate in medium-sized and large specimens. Outside of valves with 10 to 17 main radial ribs, often bearing scale-like spines, and with weaker interstitial.. more