Sphaeridium \Sphae*rid"i*um\, n.; pl. {Sphaeridia}. [NL., fr.
Gr. ??? a sphere.] (Zool.)
A peculiar sense organ found upon the exterior of most kinds
of sea urchins, and consisting of an oval or sherical head
surmounting a short pedicel. It is generally supposed to be
an olfactory organ.
[1913 Webster]