The Collaborative International Dictionary of English v.0.48:

Massasauga \Mas`sa*sau"ga\, n. (Zool.)
   The black rattlesnake (Crotalus tergemina, or Caudisona
   tergemina), found in the Mississippi Valley.
   [1913 Webster] Masse shot

WordNet (r) 3.0 (2006):

massasauga
    n 1: small pygmy rattlesnake [syn: ground rattler,
         massasauga, Sistrurus miliaris]
    2: pygmy rattlesnake found in moist areas from the Great Lakes
       to Mexico; feeds on mice and small amphibians [syn:
       massasauga, massasauga rattler, Sistrurus catenatus]