This remarkably fine species, peculiar in its colored columella, is ruder and larger and more thick-skinned in the north ; smaller, more elegantly sculptured, whiter, and with less epidermis in the Gulf of Mexico. This form, which rarely exceeds 25 mm. in length, and has the color on the pillar very faint or absent, may take the varietal name of mexicana. After a careful comparison of the young of this species with an authentic specimen of Pleurotomella sandersoni, I am much inclined to the opinion that the latter is merely a more slender variety with the transverse ripples on the anal fasciole finer and more numerous. I can see no other differences. The name may be retained in a varietal sense.