The Collaborative International Dictionary of English v.0.48:

Mammillate \Mam"mil*late\, Mammillated \Mam"mil*la`ted\, a. [See
   Mammilla.]
   1. Having small nipples, or small protuberances like nipples
      or mammae.
      [1913 Webster]

   2. (Zool.) Bounded like a nipple; -- said of the apex of some
      shells.
      [1913 Webster]