The new gonyaulacoid dinoflagellate Pentadinium galileoi Sancay et al., sp. nov. from the Oligocene-Lower Miocene sediments of Eastern Anatolia has been identified. It is spherical, chordate with prominant discoidal cingulum and distally furcate apical, sulcal, and antapical processes. It has a type P (3″) archeopyle, and periarcheopyle is larger than endoarcheopyle. Tabulation is distinct and it has a formula of 1pr, 3–4′, 6″,6c, 6‴, 1p, 1″″. Wall structure is granular in intraplate areas, and it has gonal spines at apex, posterior intercalary, and antapex. Processes at gonal positions may be on a variably developed antapical ‘skirt’ formed by extended septa (2–3 μm), minute bifurcate spines intergonally and along cingulum at plate intersections. Periphragm and endophragm appressed except at cingular area and at septa. The size of the cysts ranges between 73–89μm with an avarage of 84μm.