gray comma

from The Collaborative International Dictionary of English v.0.48

Progne \Prog"ne\ (pr[o^]g"n[-e]), n. [L., a swallow,
   traditionally said to be fr. Progne (The sister of
   Philomela), who was changed into a swallow, Gr. Pro`knh.]
   (Zool.)
   (a) A swallow.
   (b) A genus of swallows including the purple martin. See
       {Martin}.
   (c) An American butterfly ({Polygonia Progne} syn. {Vanessa
       Progne}). It is orange and black above, grayish beneath,
       with an L-shaped silver mark on the hind wings. Called
       also {gray comma}.
       [1913 Webster]