sistrurus

from The Century Dictionary.

• noun A genus of rattle-snakes distinguished by having the top of the head covered with plates (as in harmless snakes and the Proteroglypha) instead of scales. There are but three species, two of which occur in the United States. The best known is the massasauga.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun pygmy rattlesnakes