In the Peruvian Pachakuti Mesa tradition the shell symbolizes Mama Qocha, or Mother Ocean, which is the container of all life. The oceans in turn are associated with Mama Killa or Grandmother Moon as curanderos have long been aware of the moon?s ability to control the water or unu in Q'echua. Not only does Mama Killa regulate the tides of the oceans, her energy has a powerful affect on water in general, influencing even the water contained within our bodies. Water is also a symbol of human emotion and the unconscious aspect of the self. So by placing a shell in the west of your mesa or altar ground you to can connect with your emotions and the ebb and flow of the oceans.

Source: Peruvian Shamanism: The Pachakuti Mesa by Matthew Magee