During a survey of epilithic diatoms in the running water of the main island of New Caledonia, a new species was found: Adlafia diahotensis Le Cohu, Marquié & Tudesque, sp. nov. This species is characterized by the valve outline with ends wedge shaped obtusely rounded. In light microscopy, the striae are only discernible in the center of the valve. In scanning electron microscopy, the internal proximal raphe endings are shortly deflected towards the primary side of the valve and far apart from each other.