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Histiocysta
From Williams et al., 2017:
[Histiocysta, Davey, 1969a, p. 138
Type species: Histiocysta palla, Davey, 1969a (pl.1, fig.5; text-figs.14A–B)]
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Original description: [Davey, 1969]:
Description:
Proximate cysts, spherical to subspherical; shell wall composed of two layers; outer layer giving rise to low crests. Crests reflecting Gonyaulax-type tabulation and coarse, subsidiary reticulation within plate boundaries. Sutural crests better defined than crests of subsidiary reticulation. Archaeopyle apical with angular margin. Operculum probably single apical plate.
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Modified description:
Stover and Evitt, 1978, p. 52-53:
Synopsis:
Cysts proximate, subspherical, with parasutural ridges or septa and intratabular reticulation; paratabulation probably gonyaulacacean; archeopyle apical, Type (tA) or (tAa).
Description:
Shape: Subspherical.
Wall relationships: Endophragm and periphragm appressed, latter giving rise to parasutural and intratabular features.
Wall features: Parasutural ridges or septa low, fairly continuous. Intratabular areas with discontinuous curved ridges, which form an imperfect reticulum.
Paratabulation: Indicated principally by parasutural features and secondarily by intratabular ornamentation, probably gonyaulacacean; precise formula unknown.
Archeopyle: Apical, Type tA or tAa, more commonly the latter; operculum small, representing one or four antapical paraplates.
Paracingulum: Indicated by six transversely elongate, rectangular paraplates.
Parasulcus: Generally not indicated.
Size: Small.
Affinities:
Histiocysta differs from Cassiculosphaeridia and from Ellipsoidictyum in having parasutural features in addition to the paracingulum. In general appearance, Histiocysta resembles Microdinium, which also has an apical archeopyle. Because information about the paratabulation on Histiocysta is incomplete, further comparison of the two genera is precluded.
[Histiocysta, Davey, 1969a, p. 138
Type species: Histiocysta palla, Davey, 1969a (pl.1, fig.5; text-figs.14A–B)]
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Original description: [Davey, 1969]:
Description:
Proximate cysts, spherical to subspherical; shell wall composed of two layers; outer layer giving rise to low crests. Crests reflecting Gonyaulax-type tabulation and coarse, subsidiary reticulation within plate boundaries. Sutural crests better defined than crests of subsidiary reticulation. Archaeopyle apical with angular margin. Operculum probably single apical plate.
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Modified description:
Stover and Evitt, 1978, p. 52-53:
Synopsis:
Cysts proximate, subspherical, with parasutural ridges or septa and intratabular reticulation; paratabulation probably gonyaulacacean; archeopyle apical, Type (tA) or (tAa).
Description:
Shape: Subspherical.
Wall relationships: Endophragm and periphragm appressed, latter giving rise to parasutural and intratabular features.
Wall features: Parasutural ridges or septa low, fairly continuous. Intratabular areas with discontinuous curved ridges, which form an imperfect reticulum.
Paratabulation: Indicated principally by parasutural features and secondarily by intratabular ornamentation, probably gonyaulacacean; precise formula unknown.
Archeopyle: Apical, Type tA or tAa, more commonly the latter; operculum small, representing one or four antapical paraplates.
Paracingulum: Indicated by six transversely elongate, rectangular paraplates.
Parasulcus: Generally not indicated.
Size: Small.
Affinities:
Histiocysta differs from Cassiculosphaeridia and from Ellipsoidictyum in having parasutural features in addition to the paracingulum. In general appearance, Histiocysta resembles Microdinium, which also has an apical archeopyle. Because information about the paratabulation on Histiocysta is incomplete, further comparison of the two genera is precluded.