Isodiscus Rattray: a problematic fossil marine genus

Abstract

The fossil marine genus Isodiscus Rattray presently comprises three species, I. debyi (E. Grove & G. Sturt) Rattray, I. mirificus Rattray and I. coronalis Brun; all are rare. One new species I. watanabei is described here. The genus is confined to the middle to late Eocene and its morphological features present difficulties in assigning it to a family or order. A new family Isodiscaceae is proposed and relationships discussed.