Ulnaria wuling-biseriata, sp. nov., external view, SEM A a complete valve B middle detail from A, showing the rectangular central area C, D two apical details of A, note some uniseriate striae at the apices E another complete valve F middle detail from E, showing a trapezoidal central area. Scale bars: 20 μm (A, E); 2 μm (B–D, F).