4 Medium to Large Size Hermit Crab Changing ShellsSize Range: 1 1/2” 2 1/2" (38-63mm)Opening Range: 5/8" - 1 3/4" (28-38mm)Great for Medium to Large Hermit Crabs. Shells include Rapana Whelks and Polished Turbo Shells with clean and smooth Openings. All Natural Seashells, Aquarium Safe.