Psammothidium harveyi

Valves are elliptic-lanceolate with rostrate apices. The raphe valve has a narrow linear axial area widening at the valve center into a transversely rectangular asymmetric central area that often reaches the valve margins. The raphe is straight, but its short terminal fissures are gently curved to opposite sides. The proximal external raphe ends are expanded and sharply turned to the same side in SEM, but appear straight in LM. The axial area on the rapheless valve is linear and widens into an asymmetric central area. The striae are uniseriate. The external areolae openings are mostly isodiametric, but transapically elongated near valve margins. Internally, areolae are transapically elongated. There are 23–28 areolae in 10 μm along each stria on the rapheless valve and 28–35 on the raphe valve. The girdle bands are plain and open.