Some of the pink-striped Panama varieties, though having a somewhat different aspect, can be distinguished from certain varieties of _B. amphitrite_ only by their scuta being longitudinally striated,--a character in this species variable in degree, and in most cases of very little value. Some of the other recent varieties are sufficiently distinct from _B. amphitrite_; and the great fossil Coralline Crag specimens, which stand at the opposite end of the series of varieties, with their ribbed walls, very oblique radii, and coarsely striated scuta, are extremely unlike _B. amphitrite_. With respect to the nomenclature of the present species, I have little doubt that I have properly identified the Italian fossil specimens with _B. concavus_ of Bronn, who has given a very good figure of this species in his 'Lethæa Geognostica;' it must, however, be confessed that the longitudinal striæ on the scuta are not there represented. Considering the large size and frequency of this species in Europe and in the United States, it has probably received several other names, besides the two incorrect synonyms, quoted at the head of this description. I should add that the true _B. cylindraceus_ (not _var._ C) of Lamarck, according to the plate given by Chenu in his 'Illust. Conch.,' is the _B. psittacus_ of South America. I have seen in collections specimens of _B. concavus_ labelled as _B. tulipa_ of Poli (_B. tulipiformis_ of this work),--a very natural mistake, without the opercular valves be carefully examined. _General Appearance._--Shell conical, often steeply conical; orifice rather small, with the radii narrow, and generally in the fossil specimens very oblique; surface generally smooth, sometimes rugged, and in the coralline crag specimens generally ribbed longitudinally, the ribs being narrow. Colour various, either dull reddish-purple with narrow nearly white, or wider dark longitudinal bands; or, again, pale rosy-pink with broad white bands; or lastly, wholly white. The radii are either darker or paler than the parietes. The opercular valves are either dark purple or nearly white. Pale pink and white stripes are visible on some of the Italian and Portuguese tertiary specimens; and in most of the fossils the sheath is tinged dull red. _Dimensions._--The largest actually recent specimen which I have seen, from the Philippine Archipelago, had a basal diameter of 1.2 of an inch; the Peruvian pleistocene specimen is 1.7 in diameter; specimens from the crag and from the Italian deposits, however, sometimes slightly exceed two inches in basal diameter, and three in height.