Several specimens referable to the species of Trigonioides(Wakinoa) tetoriensis Maeda were collected from the Tatsukawa Formation，basal formation，of the Monobegawa Group belonging to the Outer Zone of the Southwest Japan，at Tatsukawa，Katsuura area of Tokushima Prefecture，Shikoku．This species is one of the well known fresh-water conditional bivalves which had been described from the basal part of the ltoshiro Subgroup，considered to the Jurassic or Cretaceous deposits of the Tetori Group，belonging to the lnner Zone of the Southwest Japan in Hokuriku district of Japan．This is also known from the non-marine Mesozoic deposits of the Keishou Group，of Southern　Korea．Since the occurrence of this species，probably restricted narrow age in the range，is determined to the Latest Hauterivian or Early Barremian judging from that of the upper part of Tatsukawa Formation，the occurrence of this species is not only valuable to the correlation of the non-marine deposits between the Outer and lnner　Zones of the Southwest Japan but also the correlations of those among Japan，Korea and the East Asian continent．