English Class 6: What does 'shell' mean?

What does shell mean?

(1) - Search shell in the dictionaries section on the right side of the Class Blog.

(2) - Read the attached file about the Shell of Saint James.

(3) - Here there is an old song with the word shell on its title: Hide on your shell by Supertramp.

Maggi Hambling The Scallop (2003) Aldeburgh beach. 

 Photograph © Andrew Dunn, 1 November 2005.