What does "lingula" mean?

Lingula: (Zoöl.) Any one of numerous species of brachiopod shells belonging to the genus Lingula, and related genera. See Brachiopoda, and Illustration in Appendix. Lingula flags (Geol.), a group of strata in the lower Silurian or Cambrian system of Wales, in which some of the layers contain vast numbers of a species of Lingula.

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