Surirella suiningensis, sp. nov., internal view, SEM A one complete valve showing fibulae extending close to median line and fibulae corresponding to the sinking of mantle (i.e. troughs, six arrows) B detail from A showing only one portula between two adjacent fibulae and uniseriate striae C sinking of mantle against the fibulae (two arrows) D, E apical details from B, note the raphe continuous at one apex (D, arrow) whereas interrupted at the other apex (E, one arrow pointing at a helictoglossa-like process). Scale bars: 20 μm (A); 2 μm (B, C, E); 1 μm (D).