The Collaborative International Dictionary of English v.0.48:

Turnus \Tur"nus\, n. [NL., fr. L. Turnus, the king of the
   Rutuli, mentioned in the Aeneid.] (Zool.)
   A common, large, handsome, American swallowtail butterfly,
   now regarded as one of the forms of Papilio glaucus syn.
   Jasoniades glaucus. The wings are yellow, margined and
   barred with black, and with an orange-red spot near the
   posterior angle of the hind wings. Called also tiger
   swallowtail. See Illust. under Swallowtail.
   [1913 Webster]