Diploneis zannii Frenguelli (1933: 415, pl. IV, fig. 10) (Figs 1–23) Description: LM (Figs 1–16). Valves elliptic-lanceolate (length 37.5–57.5 μm, breadth 27–36 μm, L/B: 1.7–2.2). Longitudinal canals occupying 1/3 of valve width, together forming a narrow lanceolate area. Striae uniseriate, slightly radial at valve center (8–10/10 μm), strongly radial at poles (10–11/10 μm), interrupted at canals. SEM (Figs 17–23). Raphe filiform (Figs 17–19) with external proximal ends straight located at bottom of a depression (Fig. 18); distal ends curved in obtuse angle (Fig. 19) to the same side. Longitudinal canals with one row of areolae separated from striae by conspicuous hyaline area (Figs. 17–19). Externally, each alveolus opens as a uniseriate stria composed of equidistant areolae (10–12/10 μm) (Figs 18–19). Internally, raphe straight, running through sunken area between longitudinal canals (Figs 20–22); proximal and distal ends simple, helictoglossae slightly developed (Figs 21–22). Transapical ribs straight delimiting alveoli (Figs 20–23). Transapical ribs fungiform in transverse section (Fig. 23, arrows). Areolae open in single foramina (Figs 21, 23, arrowheads). Type: — ARGENTINA. Corrientes: Itatí Rincón Lagoon, Esteros del Iberá, 28°42’00’’S; 58°06’00’’W, J. Frenguelli, 24 February 1941 (lectotype designated here, Frenguelli Collection! 268, slide 268 (3), England Finder: N 47 (4), here illustrated as Figs 14–16; Isolectotype designated here: Frenguelli Collection! 268, Slides 268 (1–3, 6, 8, 15, 16).

Published as part of Vouilloud, Amelia A., Sala, Silvia E. & Heguilor, Santiago, 2018, Revision of the type material of Diploneis zannii Frenguelli (Bacillariophyceae), pp. 239-245 in Phytotaxa 351 (3) on page 240, DOI: 10.11646/phytotaxa.351.3.5, http://zenodo.org/record/13707252