Abstract
Imparvalvia, a new genus of araphid diatoms, is described from the Miocene marine sediments of the Koitoi Formation, Hokkaido, Japan. This monotypic genus is represented by Imparvalvia laevigata sp. nov., of linear-lanceolate form, which has a heterovalvar frustule consisting of a simple hyaline epivalve and more intricate-structural hypovalve furnished with the paraseptum. There is no areolation excluding several pores on the frustule.
The genus should be placed in a new family, named Imparvalviaceae, due to its highly distinctive nature.
