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Sirmiodinium
From Williams et al., 2017:
[Sirmiodinium, Alberti, 1961, p. 22. Emendation: Warren, 1973, p.104
Type species: Sirmiodinium grossii, Alberti, 1961 (pl.7, fig.6); emend. Warren, 1973]
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Original description: [Alberti 1961]: (Translation: Stover and Evitt, 1978, p. 220):
Diagnosis:
Shell flattened, in outline approximately pentagonal (almost hexagonal). Inner body oval to rounded hexagonal, particularly fattened at the antapical pole. An outer swelling, which is interrupted in the region of the equator by a transverse furrow, encloses the inner body in a narrow marginal zone (dorsal and ventral). By this means a more or less ellipsoidal central part of the ventral and dorsal sides remains free of the surrounding shell. The epitheca and the slightly larger hypotheca form two trapezoids of unequal size joined at their bases; the antapical outer edge is slightly concave. Thus two slightly diverging antapical protrusions at the outer ends are sometimes indicated. Epitheca with a short, projecting apical protrusion.
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Emended description:
Warren, 1973, p. 104:
Description:
Cyst dorso-ventrally flattened, pentagonal to trilobate in dorsal or ventral view. Two walls, in contact on dorsal and ventral surfaces, separated at ambitus. Where separated from endophragm, periphragm is perforated by various small openings, always at antapex, commonly in reflected cingulum and on epitract, rarely on lateral hypotract; openings in reflected cingulum may coalesce, causing periphragm to be absent from lateral portions of reflected cingulum. Blunt apical horn present.
Tabulation distinct to nearly indiscernible, reflected by low sutural ridges on perophragm; plate formula 4`, 6``, 6```, 1p, 1````. Reflected cingulum low spiral; reflected sulcus straight.
Archaeopyle apical plus precingular. Operculum in two pieces; one corresponds to apical plates, attached along anterior edge of reflected plate 6``, and reflected sulcus, or free; the other corresponds to plate 3``, attached at reflected cingulum.
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Modified description:
Stover and Evitt 1978, p. 220-221:
Synopsis:
Cysts circumcavate, dorso-ventrally flattened, outline rounded pentagonal to strongly trilobate with short apical protrusion; gonyaulacacean; paratabulation nearly indiscernible to distinct, indicated by low parasutural ridges or pandasuturate areas; combination archeopyle, Type tAa+Pa.
Description:
Shape: Rounded pentagonal to strongly trilobate with short apical projection.
Wall relationships: Cysts circumcavate; separation between wall layers greatest on hypocyst.
Wall features: Low parasutural ridges or striate pandasuturate areas present on the periphragm, which is otherwise smooth or faintly ornamented, locally perforate; endophragm scabrate to granulate; pandasuturate areas clearest on hypocyst.
Paratabulation: Nearly indiscernible to distinct, indicated by low parasutural ridges and pandasuturate areas: gonyaulacacean, formula: 4`, 6``, 6c, 6```, 1p, 1````, 0-5s.
Archaeopyle: Combination, Type tAa+Pa; operculum composed of two pieces - one corresponds to apical paraplates, the other to paraplate 3``. Each opercular piece normally attached with the apical piece adherent ventrally to paraplate 6`` and the parasulcus; precingular piece adherent along its antapical margin.
Paracingulum: Normally indicated by low, parallel, transverse parasutural ridges; expression over cavate region at sides may be by ridges only, by a depression, or by a zone of perforations.
Parasulcus: Somewhat teardrop-shaped area, undivided or subdivided into a maximum of five sulcal paraplates plus pore scars.
Size: Intermediate to large.
Affinities:
Sirmiodinium differs from Scriniodinium in having a combination Type tAa+Pa archeopyle rather than a simple precingular Type P archeopyle. In general, the paracingulum is expressed more clearly on Sirmiodinium, and the paratabulation is indicated by parasutural and pandasuturate features as opposed to the parasutural features alone of Scriniodinium.
[Sirmiodinium, Alberti, 1961, p. 22. Emendation: Warren, 1973, p.104
Type species: Sirmiodinium grossii, Alberti, 1961 (pl.7, fig.6); emend. Warren, 1973]
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Original description: [Alberti 1961]: (Translation: Stover and Evitt, 1978, p. 220):
Diagnosis:
Shell flattened, in outline approximately pentagonal (almost hexagonal). Inner body oval to rounded hexagonal, particularly fattened at the antapical pole. An outer swelling, which is interrupted in the region of the equator by a transverse furrow, encloses the inner body in a narrow marginal zone (dorsal and ventral). By this means a more or less ellipsoidal central part of the ventral and dorsal sides remains free of the surrounding shell. The epitheca and the slightly larger hypotheca form two trapezoids of unequal size joined at their bases; the antapical outer edge is slightly concave. Thus two slightly diverging antapical protrusions at the outer ends are sometimes indicated. Epitheca with a short, projecting apical protrusion.
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Emended description:
Warren, 1973, p. 104:
Description:
Cyst dorso-ventrally flattened, pentagonal to trilobate in dorsal or ventral view. Two walls, in contact on dorsal and ventral surfaces, separated at ambitus. Where separated from endophragm, periphragm is perforated by various small openings, always at antapex, commonly in reflected cingulum and on epitract, rarely on lateral hypotract; openings in reflected cingulum may coalesce, causing periphragm to be absent from lateral portions of reflected cingulum. Blunt apical horn present.
Tabulation distinct to nearly indiscernible, reflected by low sutural ridges on perophragm; plate formula 4`, 6``, 6```, 1p, 1````. Reflected cingulum low spiral; reflected sulcus straight.
Archaeopyle apical plus precingular. Operculum in two pieces; one corresponds to apical plates, attached along anterior edge of reflected plate 6``, and reflected sulcus, or free; the other corresponds to plate 3``, attached at reflected cingulum.
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Modified description:
Stover and Evitt 1978, p. 220-221:
Synopsis:
Cysts circumcavate, dorso-ventrally flattened, outline rounded pentagonal to strongly trilobate with short apical protrusion; gonyaulacacean; paratabulation nearly indiscernible to distinct, indicated by low parasutural ridges or pandasuturate areas; combination archeopyle, Type tAa+Pa.
Description:
Shape: Rounded pentagonal to strongly trilobate with short apical projection.
Wall relationships: Cysts circumcavate; separation between wall layers greatest on hypocyst.
Wall features: Low parasutural ridges or striate pandasuturate areas present on the periphragm, which is otherwise smooth or faintly ornamented, locally perforate; endophragm scabrate to granulate; pandasuturate areas clearest on hypocyst.
Paratabulation: Nearly indiscernible to distinct, indicated by low parasutural ridges and pandasuturate areas: gonyaulacacean, formula: 4`, 6``, 6c, 6```, 1p, 1````, 0-5s.
Archaeopyle: Combination, Type tAa+Pa; operculum composed of two pieces - one corresponds to apical paraplates, the other to paraplate 3``. Each opercular piece normally attached with the apical piece adherent ventrally to paraplate 6`` and the parasulcus; precingular piece adherent along its antapical margin.
Paracingulum: Normally indicated by low, parallel, transverse parasutural ridges; expression over cavate region at sides may be by ridges only, by a depression, or by a zone of perforations.
Parasulcus: Somewhat teardrop-shaped area, undivided or subdivided into a maximum of five sulcal paraplates plus pore scars.
Size: Intermediate to large.
Affinities:
Sirmiodinium differs from Scriniodinium in having a combination Type tAa+Pa archeopyle rather than a simple precingular Type P archeopyle. In general, the paracingulum is expressed more clearly on Sirmiodinium, and the paratabulation is indicated by parasutural and pandasuturate features as opposed to the parasutural features alone of Scriniodinium.