What is "bivium"

Bivium \Biv"i*um\, n. [L., a place with two ways. See Bivious.] (Zo["o]l.) One side of an echinoderm, including a pair of ambulacra, in distinction from the opposite side (trivium), which includes three ambulacra.

n. (context zoology English) One side of an echinoderm, including a pair of ambulacra, in distinction from the opposite side ((term trivium English)), which includes three ambulacra.