One decapod crustacean species, Portunus withersi (Glaessner, 1933), from Guri Member (early Miocene) from the Mishan Formation of Hormozgan Province, Southern Iran is reported. This species previously was described in the Fars area, but this is the first report from this area. This species confirms the early Miocene age; the lower boundary of the Guri Member is coincident with the lower Miocene. Recognition of the age of this member is very important because the lower boundary of the Guri member ranges from early to middle Miocene from the west to east in the Zagros Basin. This member north of Bandar-Abbas is older than it is in the west of the Basin. This paper introduces only the second report of Cenozoic crustaceans from the Zagros Basin. Thin sections of the carbonate unit have been studied in order to interpret the sedimentary environment. Studied allochems confirmed an open lagoon and some patch reefs with high flow of sea water

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