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Xenikoon
From Fensome et al., 2019:
Xenikoon Cookson and Eisenack, 1960a, p.14–16.
Type: Cookson and Eisenack, 1960a, pl.3, fig.17, as Xenikoon australis.
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Original description [Cookson and Eisenack, 1960]:
Shell ovoidal, slightly pointed anteriorly, containing a spherical capsule, the wall of which is in direct contact with the wall of the shell except at the anterior end. A pylome is present shortly below the apex. In one example, which unfortunately is damaged, the shell seems to have been enclosed in a smooth, outer membrane.
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Modified description:
Stover and Evitt, 1978, p. 133:
Synopsis:
Cysts proximate, epicavate, lenticular ellipsoidal, without distinct apical and antapical horns; endophragm outline elliptical, length greater than width; apical pericoel broad and low, always present; paratabulation indicated by archeopyle only, latter intercalary, Type l; archeopyle index <0.5.
Description:
Shape: Lenticular ellipsoidal.
Wall relationships: Cyst epicavate, endophragm and periphragm separated at apical end, pericoel relatively low.
Wall features: No parasutural features. Periphragm smooth, or faintly and uniformly ornamented.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Intercalary, Type I or la (2a only); archeopyle index <0.5, generally about 0.4; whether operculum is normally free or attached is unknown.
Paracingulum: Not indicated.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
Xenikoon differs from Nelsoniella in having a smaller (lower) apical pericoel. In addition, some species of Nelsoniella have an apical horn or protrusion. Xenikoon differs from Amphidiadema in lacking an antapical pericoel.
Xenikoon Cookson and Eisenack, 1960a, p.14–16.
Type: Cookson and Eisenack, 1960a, pl.3, fig.17, as Xenikoon australis.
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Original description [Cookson and Eisenack, 1960]:
Shell ovoidal, slightly pointed anteriorly, containing a spherical capsule, the wall of which is in direct contact with the wall of the shell except at the anterior end. A pylome is present shortly below the apex. In one example, which unfortunately is damaged, the shell seems to have been enclosed in a smooth, outer membrane.
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Modified description:
Stover and Evitt, 1978, p. 133:
Synopsis:
Cysts proximate, epicavate, lenticular ellipsoidal, without distinct apical and antapical horns; endophragm outline elliptical, length greater than width; apical pericoel broad and low, always present; paratabulation indicated by archeopyle only, latter intercalary, Type l; archeopyle index <0.5.
Description:
Shape: Lenticular ellipsoidal.
Wall relationships: Cyst epicavate, endophragm and periphragm separated at apical end, pericoel relatively low.
Wall features: No parasutural features. Periphragm smooth, or faintly and uniformly ornamented.
Paratabulation: Indicated by archeopyle only.
Archeopyle: Intercalary, Type I or la (2a only); archeopyle index <0.5, generally about 0.4; whether operculum is normally free or attached is unknown.
Paracingulum: Not indicated.
Parasulcus: Not indicated.
Size: Intermediate.
Affinities:
Xenikoon differs from Nelsoniella in having a smaller (lower) apical pericoel. In addition, some species of Nelsoniella have an apical horn or protrusion. Xenikoon differs from Amphidiadema in lacking an antapical pericoel.