Source : Webster's Revised Unabridged Dictionary (1913)

Costate \Cos"tate\ (k?s"t?t), Costated \Cos"ta*ted\ (-t?-t?d),
   a. [L. costatus, fr. costa rib.]
   Having ribs, or the appearance of ribs; (Bot.) having one or
   more longitudinal ribs.

Source : WordNet®

costate
     adj 1: (of the surface of shells) having a rough, rib-like texture
            [syn: {ribbed}]
     2: having ribs