mammals of the family Phocoenidae comprising four genera found in the North pacific ocean and both sides of the North atlantic ocean and in various other seas. They differ from dolphins in that porpoises have a blunt snout and a rather stocky body while dolphins have a beak-like snout and a slender, streamlined body. They usually travel in small groups. (From Walker's mammals of the World, 5th ed, pp1003-4)