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Kids will love making these beachy terra-cotta plant pots using snail shells, Atlantic cockles, quahogs, or black calico scallops.

Use craft glue or hot glue to attach shells of uniform size. Start with a ring of shells at the top (shells should extend above the rim of the pot) and work downward, placing each successive row about halfway down the shells on the previous ring.

From -  http://www.marthastewart.com/photogallery/nature-crafts-for-kids#slide_18&xsc=eml_crd_2010_06_21