It has generally been assumed that Nucella lapillus reaches maturity after three years, and that the adult shell does not increase in size or change shape thereafter. Most European populations reach an adult shell length of 2.5–3.5 cm, but in the Bristol Channel lives a larger form which commonly exceeds 5.0 cm. Despite high mortality rates, attempts to breed the large form in the laboratory indicate that newly hatched snails had shells shorter and squatter than those of their parents. Some juveniles grew quickly in their second year, passing the ‘normal’ adult size of 3 cm in 18 months and two laid egg eapsules at 19 months. Had they continued to grow at the same rate these juveniles would have reached parental size and shape in 3 years. However, most of the young snails grew more slowly and showed no sign of ever reaching large size. Successful rearing of Nucella in aquaria seems to require circulation of water and temperatures below 25°C.