The Collaborative International Dictionary of English v.0.48:

Cribellum \Cri*bel"lum\ (kr?b?l"l?m), n. [L., a small sieve,
   dim. of cribrum sieve.] (Zool.)
   A peculiar perforated organ of certain spiders
   (Ciniflonid[ae]), used for spinning a special kind of silk.
   [1913 Webster]