The Collaborative International Dictionary of English v.0.48:

Proscolex \Pro*sco"lex\, n.; pl. Proscolices. [NL., fr. Gr. ?
   before + ?, ?, a worm.] (Zool.)
   An early larval form of a trematode worm; a redia. See
   Redia.
   [1913 Webster]