The Collaborative International Dictionary of English v.0.48:

Oniscus \Oniscus\ prop. n.
   The type genus of the Oniscidae, consisting of woodlice
   that cannot roll into a ball.

   Syn: genus Oniscus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Oniscus
    n 1: type genus of the Oniscidae; woodlice that cannot roll into
         a ball [syn: Oniscus, genus Oniscus]