Notes on the diatom collection of the Natural History Museum, London (BM) XI: the type specimens of Actinocyclus ingens Rattray and related specimens

Actinocyclus ingens Rattray is a useful stratigraphic marker. It has been sub-divided into several 'forms' because of a presumed high degree of morphological variability: it is considered a 'polymorphic species'. The type specimens of Actinocyclus ingens, Coscinodiscus elegans Grev., Cosmiodiscus elegans Grev., and Coscinodiscus perikompsos var. curta Rattray are examined and commentary is made on the meaning of sub-specific categories. For nomenclatural reasons, detailed within, Actinocyclus ingens requires a new name. This paper primarily concerns names.