DELTHYRIS

‖Del‐thy″ris (?), n. [[NL., fr. Gr. δέλτα the name of the letter Δ + θύρα door.]] (Zoöl.) A name formerly given to certain Silurian brachiopod shells of the genus Spirifer. Delthyris limestone (Geol.), one of the divisions of the Upper Silurian rocks in New York.