Fimbria fimbriata Linnaeus 1758 is an infaunal inhabitant of coral sands in the Indo-Pacific. The structure and mineralogy of the shell (Taylor, Kennedy and Hall, 1973) confirms its taxonomic position as a member of the Lucinacea. Nicol (1950) erected (giving no reasons) a new family, taking its name (the Fimbriidae) from the genus. This study supports the view of Alien and Turner (1970) and Boss (1970) that Fimbria is closely related to the Lucinidae Fleming 1828 though a study of fossil fimbriids will have to be undertaken before the extreme view of Alien and Turner (1970) that Fimbria is a lucinid, can be validated. The Lucinidae and F. fimbriata possess the following features in common: (1) An enlarged anterior half of the shell with an antero-dorsal inhalant stream. (2) A single (inner) demibranch with type G ciliation (Atkins, 1937b). (3) Reduced labial palps. (4) "Mantle palps". (5) A stomach closely similar in structure. (6) A unique method of withdrawing the posterior exhalant siphon.