This classic series consists of 6 different seashells wonderfully made and detailed by PY / Miyao company from Japan in the 1960s. A correct pair consists of two identical shells, but they are marked with a little black "S" and "P" respectively. Each set is small - only 1'' to 1.75'' tall. Have you found them all yet?
This series was published in Irene Thornburg's The Big Book of Salt & Pepper Shaker Series on page 88 and 89.