In this preliminary report the writers treated the following noteworthy seaweeds collected in Hakata Bay. 1) A probably new species of the genus Vaucheria was collected in this bay. This is the first time that this genus has been found in Japanese sea water. 2) A new species of the genus Tinocladia was collected in this bay. The species differs from the other species in having a simplex frond. A new name, Tinocladia simplex Segawa et Ohta, has been provided. 3) Using the materials of this bay the procarp development of the socalled Gloiosiphonia capillaris has been studied. In the European materials of G. capillaris the procarpial branch arises from. the basal cell of a lateral branch, while in the writers' materials it arises from the infracortical cell. The difference seems so important that it is difficult to identify the writers' specimen with G. capillaris of Europe.