(Moll & Roch)
Shell brittle, globular and equivalve. Inequilateral, umbones are bulbous, in the anterior half. Outline is irregular, both ends notched and gaping, the auricle projecting posteriorly in the median line.
Sculpture as follows: anterior lobe with up to 100 fine serrated ridges, all parallel with the upper margin of the anterior gape; anterior disc with the serrated ridges from the anterior lobe directed obliquely, from the umbones to the ventral margin, and terminating on the anterior border of the median disc; median disc, a shallow groove, smooth with numerous concentric lines; posterior disc, smooth with concentric lines; smooth auricle.
Hinge line is curved, running posteriorly directly in the dorsal line of the auricle. Interior with dorsal and ventral condyles; a median low groove; an apophysis; the posterior adductor scar on the auricle, the anterior in front of the umbones. The anterior border of the auricle is deeply ridged dorsally, less so ventrally. The stalk is sometimes half as long as the total length and to it are attached successively larger cones laid into each other. The periostracal margin of each cone carries long slender serrations.
Up to 7 cm in length.
White. Interior of shell is pearly white.
Not native in the North Sea but has been reported from various localities in drifting wood (Distr. B. fimbriatula); its main centre of distribution is the West Indies.