What is "umbrella shell"

Umbrella \Um*brel"la\, n. [It. umbrella, fr. ombra a shade, L. umbra; cf. L. umbella a sunshade, a parasol. Cf. Umbel, Umbrage.]

1. A shade, screen, or guard, carried in the hand for sheltering the person from the rays of the sun, or from rain or snow. It is formed of silk, cotton, or other fabric, extended on strips of whalebone, steel, or other elastic material, inserted, or fastened to, a rod or stick by means of pivots or hinges, in such a way as to allow of being opened and closed with ease. See Parasol.

   Underneath the umbrella's oily shed.
   --Gay.

2. (Zo["o]l.) The umbrellalike disk, or swimming bell, of a jellyfish.

3. (Zo["o]l.) Any marine tectibranchiate gastropod of the genus Umbrella, having an umbrella-shaped shell; -- called also umbrella shell.

   Umbrella ant (Zo["o]l.), the sauba ant; -- so called because it carries bits of leaves over its back when foraging. Called also parasol ant.

   Umbrella bird (Zo["o]l.), a South American bird ( Cephalopterus ornatus) of the family Cotingid[ae]. It is black, with a large handsome crest consisting of a mass of soft, glossy blue feathers curved outward at the tips. It also has a cervical plume consisting of a long, cylindrical dermal process covered with soft hairy feathers. Called also dragoon bird.

   Umbrella leaf (Bot.), an American perennial herb ( Dyphylleia cymosa), having very large peltate and lobed radical leaves.

   Umbrella shell. (Zo["o]l.) See Umbrella, 3.

   Umbrella tree (Bot.), a kind of magnolia ( Magnolia Umbrella) with the large leaves arranged in umbrellalike clusters at the ends of the branches. It is a native of Pennsylvania, Virginia, and Kentucky. Other plants in various countries are called by this name, especially a kind of screw pine ( Pandanus odoratissimus).