Abstract
Three new monospecific genera, H-shaped in girdle view, are described from the early Miocene marine deposits of the Boso Peninsula, central Japan. Tetralophus endocampus gen. et sp. nov., Orthosoma polyporophorum gen. et sp. nov., and Dendrogonia polygoniata gen. et sp. nov. are all bipolar with tall or low elevations and chain-forming by apposition of summit plates or the whole of the valve face is without an ocellus or pseudocellus. Linking spines are present or lacking on the tips of the elevations. The three new genera are placed in the Biddulphiales.
