From Fensome et al., 2019:
Hystrichosphaeridium recurvatum ssp. parvum (Rozen, 1965, p.303–304, pl.4, fig.6; text-fig.13) Lentin and Williams, 1973, p.79. Holotype: Rozen, 1965, pl.4, fig.6; text-fig.13. Originally Hystrichosphaeridium recurvatum var. parvum,
subsequently (and now) Hystrichosphaeridium recurvatum subsp. parvum, thirdly Hystrichosphaeridium palmatum subsp. parvum (combination illegitimate), fourthly Hystrichosphaeridium duplum subsp. parvum (combination illegitimate). Age: Late Eocene.

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