Middle Ordovician microplankton from the Grötlingbo borehole no. 1 in Gotland, Sweden

The present study deals with a group of Middle Ordovician phytoplankton with organic tests derived from a continuously cored well drilled at Grötlingbo in Gotland, Sweden. Twenty-two species belonging to the genera Aremoricanium, Baltispbaeridium, Electoriskos, Goniosphaeridiwn, Orthospbaeridium, and Peteinosphaeridiunt are described. Eleven new species are proposed: Baltisphaeridium brevituberculatum n. sp., B. folkeslundianum n. sp., B. magnoporatum n. sp., B. multitrabeculosum n. sp., B. pauciverrucosum n. sp., B. pustulatum n. sp., B. regnellii n. sp., Goniosphaeridiwn multipustulosum n. sp., Orthospbaeridium densigranosum n. sp., O. densiverrucosum n. sp., and Peteinosphaeridium asperum n. sp. The new combinations Baltisphaeridium klabavense ( Vavrdova,1965) and Goniosphaeridiwn mocbtiensis (Gorka, 1969) and Goniosphaeridiwn uncinatum (Martin, 1965) are proposed.