The Collaborative International Dictionary of English v.0.48:

Siphonarid \Si`pho*na"rid\, n. (Zool.)
   Any one of numerous species of limpet-shaped pulmonate
   gastropods of the genus Siphonaria. They cling to rocks
   between high and low water marks and have both lunglike
   organs and gills. -- Si`pho*na"rid, a.
   [1913 Webster]