cingulum

from WordNet (r) 3.0 (2006)

cingulum
    n 1: (anatomy) an encircling structure (as the ridge around the
         base of a tooth)

from The Collaborative International Dictionary of English v.0.48

Cingulum \Cin"gu*lum\, n. [L., a girdle.] (Zool.)
   (a) A distinct girdle or band of color; a raised spiral line
       as seen on certain univalve shells.
   (b) The clitellus of earthworms.
   (c) The base of the crown of a tooth.
       [1913 Webster]