Popular name of a multivalve Cirriped (Balanus, Ellis), called also Sea-acorn, allied to the Barnacles, but without a flexible stalk, several species of which live sessile upon rocks, piles, iron pillars, and shells of other marine animals, between high and low water-mark.
1764. Croker, Dict. Arts, s.v., The great furrowed Acorn-shell … is found sticking to the rocks in the East and West Indies.
1857. Wood, Comm. Obj. Seashore, viii. 157. The entire surface of the limpet was covered with acorn-shells.
