« Shell griseous with purplish rays. Epidermis concentrically elevated, with processes arranged into radiating lines. This shell is generally supposed to inhabit the West-Indian Seas, but I have not been able to ascertain the truth of this conjecture. The elevated processes of the epidermis, on close examination, seem to be membranaceous, with fine concentric rings of shelly matter deposited on them. » – W. E. Leach: Zoological miscellany p.98. This text shows how risky it is to rely on patterns and colours to make a good description. Here, the purplish rays on a griseous background become blackish rays on a yellowish background. Hopefully, the radially arranged scales are a constant; the species name, based on these alignments, is then resistant to morphological variability.