OYSTER SHELL CALCIUM, TAB 500MG (100/BT 12BT/CS) Oyster Shell Calcium Tablets 500 mg Calcium-enhanced absorption. Nutritional supplement. Compares to Os-Cal® 500. Not Made with Natural Rubber Latex. Packaged: 100 Per Bottle, 12 Bottles Per Case Os-Cal is a registered trademark of GlaxoSmithKline.