Abstract
An expanded description of the small fossil genus Trochosira is presented, and Trochosira mirabilis Kitton, T. spinosa Kitton and T. coronata Schrader & Fenner are described and illustrated. One species hitherto placed in the genus Skeletonema, S. polychaeta Strel'nikova, is transferred to Trochosira and the characters distinguishing Trochosira and Skeletonema are discussed. The complex linking mechanism of each Trochosira species is described and illustrated. This information, together with associated characters, confirms that the genus belongs in the family Melosiraceae. Relationships with other genera and families are discussed.