The Middle Miocene foraminifera from the Shin'ichi Basin, northem Hiroshima Prefecture, are biostratigraphically analyzed in order to correlate with the benthic foraminiferal zones that are proposed for the Bihoku Group by the writer. Benthic foraminifera consist of mainly Uvigerina subperegrina in upper horizon and agglutinated forms in the uppermost horizon. The assemblage dominated by Uvigerina subperegrina is correlated with the Uvigerina subperegrina (s.l.)
Assemblage-zone and the horizon that contains agglutinated forms is correlated with the barren zone.
This biostratigraphic succession clearly reveais the presence of Foram.Sharp Line.
The Foram. Sharp Line is recognized at about 645m above sea level in the Shin'ichi basin, which level is the highest in the Middle Miocene basins of Southwest Honshu. This height is resulted from a dislocation by the thrusts developed in southern side of the Chugoku backbone range.