One day, Vishnu found out that his Valamburi Shankha had disappeared. He felt himself very annoyed. After some time, he heard the typical sound of a conch far away and recognized immediately that it was his own instrument. The sound came from the Mount Kailash.
He meditated on Lord Shiva who came in front of him and declared that if he wanted to get his conch back, he had first to address a invocation to god Valamburi Ganesh (a Ganesh form with a right-turned trunk).
Thus, Vishnu performed the puja and Ganesh sent back the conch to his owner who was very happy to recover it.
Lord Ganesha and Lord Vishnu Story