Shell shape in living and fossil (Norwich Crag) Nucella lapillus (L.) in relation to habitat

Shell shape has been examined in collections of fossil Nucella lapillus (L.) from the Norwich Crag (early Pleistocene), and compared with living populations from sites in the Firth of Forth, from the coast of Norfolk and elsewhere. Our samples of living North Sea populations show much less variation in relation to wave-exposure than Atlantic shells, and other factors can be involved. The rather tall and narrow fossil shells are appropriate for a sheltered or moderately sheltered site, such as a bay or firth or restricted sea, but caution must be exercised in such comparisons. The mechanism determining shell form is discussed.