Abstract
Stephanodiscus komoroensis sp. nov. is described from a lacustrine diatomite of the Uryuzaka Formation which is inferred to be Lower Pleistocene. The new species is characterized by rimoportulae with triangular tips at the tops of externally elongated, thick tubes, a complete absence of spines, and mantle fultoportulae that lack any vestiges of external tubuli. Stephanodiscus komoroensis is morphologically most similar to S. niagarae Ehrenberg and S. rotula (Kültzing) Hendey.