(Balech) nov. comb.
Peridinium concavum ssp. radius Balech, 1971: 134, Pl. XVI (541-457)
After Balech, 1976: Length 44-53µm, width 41-45µm. Closer to the smaller specimens of P. concavum but shorter and relatively wider, with longer spines emerging from two small horns, largely diverging. Frequently para. Cingulum slightly but decidedly excavated.
After Balech, 1976: Though the typical specimens are quite different from the typical P. concavum this taxon was first described as a subspecies, because some individuals somewhat intergrades and their plate pattern are essentially of the same type. However the difference in suclcul plates seem constant and therefore they justify its raising to the specific rank.
This species is rarely reported. www.algaebase.org lists this species as 'p' indicating it has not been subject to any kind of verification.