Source : Webster's Revised Unabridged Dictionary (1913)

Delthyris \Del*thy"ris\, n. [NL., fr. Gr. de`lta the name of the
   letter [Delta] + thy`ra door.] (Zo["o]l.)
   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.