The Collaborative International Dictionary
Deltidium
Deltidium \Del*tid"i*um\, n. [NL., fr. Gr. de`lta, the letter [Delta].] (Zo["o]l.) The triangular space under the beak of many brachiopod shells.
Wiktionary
deltidium
n. (context zoology English) The triangular space under the beak of many brachiopod shells.