ABSTRACT. – Examination of type material of the marine diatom Anaulus vallus Nikolaev with scanning electron microscopy revealed that it possesses a canal raphe. The “pseudosepta” seen with light microscopy are actually fibulae. Based on this information, A. vallus has been transferred to the genus Denticula as Denticula vallus (Nikolaev) Sullivan. This species is morphologically quite similar to D. neritica Holmes & Croll but differs in its lack of longitudinal ribs parallel to the raphe sternum. The two taxa can not be distinguished under LM. Denticula vallus and D. neritica have been collected in abundance from seaweeds, seagrasses, and sea birds.