bubble shell

from WordNet (r) 3.0 (2006)

bubble shell
    n 1: marine gastropod mollusk having a very small thin shell

from The Collaborative International Dictionary of English v.0.48

Bubble shell \Bub"ble shell`\ (Zool.)
   A marine univalve shell of the genus {Bulla} and allied
   genera, belonging to the Tectibranchiata.
   [1913 Webster]