Source : Webster's Revised Unabridged Dictionary (1913)

Branchiostegal \Bran`chi*os"te*gal\, a. [Gr. ? gill + ? to
   cover: cf. F. branchiost[`e]ge.] (Anat.)
   Pertaining to the membrane covering the gills of fishes. --
   n. (Anat.) A branchiostegal ray. See Illustration of
   {Branchial arches} in Appendix.

   Note: This term was formerly applied to a group of fishes
         having boneless branchi[ae]. But the arrangement was
         artificial, and has been rejected.