by William Swainson

“ They are subject to variation in their colour; and this, joined with a general resemblance in form, has rendered the discrimination of the species very difficult. I have, however, remarked, that the various modifications of the umbilicus, and the termination of the pillar (which is indicated in many species by an elevated ridge or rib within the umbilicus) is a certain and constant indication, presenting the same peculiarity through all the individuals of a species, even in the young state. ”

“ Testa subglobosa seu ovalis, umbilicata. Spira depressa, brevissima. Columella umbilici medio terminans. Apertura semiorbicularis, operculo corneo vel testaceo clausa. Animal marinum, pede maximo; oculis ad basin duorum tentaculorum simplicium positis. ”