What is "sunset shell"

Sunset \Sun"set"\, Sunsetting \Sun"set`ting\, n.

1. The descent of the sun below the horizon; also, the time when the sun sets; evening. Also used figuratively.

   'T is the sunset of life gives me mystical lore.
   --Campbell.

2. Hence, the region where the sun sets; the west.

   Sunset shell (Zo["o]l.), a West Indian marine bivalve ( Tellina radiata) having a smooth shell marked with radiating bands of varied colors resembling those seen at sunset or before sunrise; -- called also rising sun.

n. A West Indian marine bivalve ((taxlink Tellina radiata species noshow=1)) having a smooth shell marked with radiating bands of varied colours resembling those seen at sunset or before sunrise.