\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.