Progonoia musca (Gregory) Schrader (1971: 922) (Figs 1–4) Basionym: Navicula musca Gregory (1857: 476) non Donkin Synonyms: Caloneis musca (Gregory) Cleve (1894: 65), Oestrupia musca (Gregory) Hustedt (1935: 17) The detail of the areolae (Fig. 4) confirms that there is no break (neither a space, nor a longitudinal line) in the coarsely porate striae as seen in LM, in contrast to the distinct longitudinal line in P. intercedens (Fig. 5) and the wider, sculpted line in P. diatreta sp. nov. (Fig. 6) (details below). Type:— UNITED KINGDOM. Arran. A micrograph of one of the two marked valves on BM 1557 is shown in Fig. 3. Reference illustrations:— Gregory 1857, pl. 9, fig. 6 (as Navicula musca) (reproduced as Fig. 1); Schmidt 1874 –1959, pl. 160, fig. 10 (reproduced as Fig. 2); Schrader 1971, pl. 1, figs 1–3, pl. 2, figs 1–4, pl. 3, figs 1, 2, 9; Round et al. 1990, pp. 550–551, figs b–d (not identified to species).

Published as part of Lobban, Christopher S., 2015, External ultrastructure of Progonoia diatreta sp. nov. (Bacillariophyta, Scoliotropidaceae) differs from P. musca and P. intercedens comb. nov., pp. 246-254 in Phytotaxa 234 (3) on pages 247-248, DOI: 10.11646/phytotaxa.234.3.5, http://zenodo.org/record/13633116