New Middle and Late Ordovician hyoliths from Estonia

Hyolith assemblages from Middle and Upper Ordovician strata in Estonia include representatives of Hyolithes Eichwald as H. gerhardi new species and H. burgessi new species, and one assigned to that genus with question. Dorsolinevitus Syssoiev is known from D. marri new species, D. dispar? (Holm, 1893) and D. textilis? (Holm, 1893); one questionable species of that genus is left in open nomenclature. Sulcavitus Syssoiev is represented by one unidentifiable species, and one incompletely preserved orthothecid constitutes the first member of that group to be recorded from Estonia. Despite the overall paucity of identifiable hyoliths from Estonia, several of the same genera are now known to be present in Estonia and Sweden, reinforcing the notion that the hyoliths of Baltica constitute a distinct biogeographic province with limited mixing of faunas from elsewhere.