Pthirus

[thĭrəs, thīrəs]
n.
  1. A genus of parasitic lice of the family Pediculidae, formerly grouped in the genus Pediculus, the main species of which is the crab louse.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.