Is that the right spelling? navajas
http://www.google.com/search?q=navajas&hl=en&lr=&rls=GWYA,GWYA:2005-51,GWYA:en&start=10&sa=N
Yes, and I have just discovered the English name, Razor clams:
http://www.productsfromspain.net/Food_from_Spain/Spanish_Food_from_Spain.html