Florida Marine Research - Hermit Shell 2Pk Lg 6Pc. Small Animal: Ornaments Packaged Large Natural Shells (2-Pack). Two larger shells up to 4 inches in size. As a crab grows and begins to protrude out of its existing shell. a new and larger shell becomes imperative. Empty shells of similar size to the crabs proper fitting shell will prevent any potential aggression of one crab toward another. Aggression is rare, however. Large 2 Pk 6 Pc Ship Dim: 9.8x6.13.8 in Ship Wt: 1.55 lb