Cyst-theca relationships in some Protoperidinium species (Peridiniales) from Scottish sea lochs

Recent dinoflagellate cysts were collected from Scottish west coast sealoch sediments and germinated to establish cyst-theca relationships. Fourteen different Protoperidinium species have been germinated and studied using the scanning electron microscope. New cysttheca relationships are described for Protoperidinium subinerme, P . thorianum and ?P. hangoei. The archeopyle of the P . excentricum cyst is described for the first time. The archeopyles of the cysts of P . pentagonum (Trinovantedinium capitatum) and P . leonis (Quinquecuspis concretum) have previously been described as representing the loss of the second intercalary paraplate, but are here considered to represent the loss of this paraplate and also the fourth precingular paraplate.