Perexiflasca tayloriana, a widespread microfossil in the Lower Devonian Rhynie chert from Scotland, consists of a thin-walled cavity surrounded by a prominent sheath. A single tube extends from the cavity to the surface. Specimens occur singly or aggregated in decaying plant tissue and on fungi. Perexiflasca tayloriana has been attributed to the Chytridiomycota and interpreted as a sheathed zoosporangium. Here we report Perexiflasca ventricosa nov. sp., a fossil from the nearby coeval Windyfield chert that corresponds to P. tayloriana in basic organization, but possesses a distinctly larger cavity and wider tube, while the sheath is proportionally less extensive. The diagnosis and description of P. tayloriana are emended. The similarities between P. tayloriana and P. ventricosa nov. sp. render attribution also of P. ventricosa nov. sp. to the Chytridiomycota a plausible option, but features of sufficient clarity to permit reliable assignment are absent. Perexiflasca ventricosa nov. sp. expands the inventory of morphologically distinct microbial fossils from the Rhynie and Windyfield cherts.