Small Spurred Turban Shells in Bulk for Small Hermit Crabs and seashell crafts, astrea calcar, measuring between approximately 3/4 inch to 1-1/2 inches (some may be over or under this size range). Calcar means spur; the outer shell has a spiral of blunt bumps and spikes. The shell is used for hermit crabs and is usually encrusted and thus well camouflaged on the rocks. Shell opening is smooth and its pearly shell is thick, flattened conical shape. The small, chalky operculum is hemi-spherical and has a smooth glossy surface. These are found in the Indo_Pacific Region.