Surirella suiningensis sp. nov., external view, SEM A one valve showing distinct continuous siliceous median ridge, downward deflecting head and foot poles (two arrows), and pattern of troughs alternating with crests B detail from A showing two troughs and one crest C, D apical details from A, note two curved terminal raphe fissures (C, two arrows) E marginal detail of A, note the recessed valve mantle with thickened base margin, no fenestrae existed, troughs on valve surface corresponding to those on the mantle (two black arrows). Scale bars: 20 μm (A); 2 μm (B–E).