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Circulodinium asymmetricum
Circulodinium asymmetricum, (Burger, 1980b, p.270, figs.6c,7a-c), He Chengquan and Sun Xuekun, 2000, p.52.
This combination was also proposed by Fauconnier in Fauconnier and Masure (2004, p.113).
Holotype: Burger, 1980b, fig.7a; Fauconnier and Masure, 2004, pl.14, fig.2.
Type locality and straticum: basal Rolling Downs Group; Zone DK3, Neocomian, probably Hauterivian
Distribution: uncommon in Helby Beds, Gilbert River Formation and basal Rolling Downs Group; Singh (1971, p1.50, fig. 2) illustrated as Canningia colliveri a comparable form from the Albian of Alberta.
Age: Neocomian.
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Original description: [Burger, 1980b]:
Description:
Cyst flattened dorsoventrally, with a pentagonal outline. Epicyst broadly triangular, ending in a short truncated apical horn, hypocyst often larger than epicyst, broad, tapering towards antapex; antapical outline asymmetrical, showing 2 unequal low bulges or broadly conical horns 8-18 µm high. Lateral corners sharp or rounded, in a few specimens with a small, wartlike protrusion.
Autophragm thin, punctate to faintly corrugate.
Tiny processes occur sparsely in equatorial region; mid-ventral and mid-dorsal areas largely free from ornament. Processes unevenly scattered and occasionally aligned, presumably along parasutures, usually more closely together and larger in antapical region. Processes wartlike, conical or tubiform, 1-4 μm high, with rounded, pointed, or bifid tips.
Archaeopyle apical, large, margin zigzag indicating 6 precingular paraplates. Operculum free.
A paracingulum is often faintly and partly indicated as a single or double fold of the cyst wall in the equatorial region.
A parasulcus is not outlined.
Dimensions:
Apical diameter (4 entire specimens) 86-100 μm; diameter of 12 dehisced specimens 64-90 μm; maximum width 77-102 μm.
Affinities:
This species is assigned to Cyclonephelium on account of its apical archaeopyle and restricted process distribution. It differs from most species of the genus by its large dimensions, asymmetrical outline with prominent antapical bulges, and the sparse, tiny processes (Fig. 6c). In outline it resembles Canningia but it differs from that genus by the uneven, restricted process distribution. Canningia hirtella (Alberti) Millioud 1969 has a shorter epicyst and longer spinules.
This combination was also proposed by Fauconnier in Fauconnier and Masure (2004, p.113).
Holotype: Burger, 1980b, fig.7a; Fauconnier and Masure, 2004, pl.14, fig.2.
Type locality and straticum: basal Rolling Downs Group; Zone DK3, Neocomian, probably Hauterivian
Distribution: uncommon in Helby Beds, Gilbert River Formation and basal Rolling Downs Group; Singh (1971, p1.50, fig. 2) illustrated as Canningia colliveri a comparable form from the Albian of Alberta.
Age: Neocomian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Burger, 1980b]:
Description:
Cyst flattened dorsoventrally, with a pentagonal outline. Epicyst broadly triangular, ending in a short truncated apical horn, hypocyst often larger than epicyst, broad, tapering towards antapex; antapical outline asymmetrical, showing 2 unequal low bulges or broadly conical horns 8-18 µm high. Lateral corners sharp or rounded, in a few specimens with a small, wartlike protrusion.
Autophragm thin, punctate to faintly corrugate.
Tiny processes occur sparsely in equatorial region; mid-ventral and mid-dorsal areas largely free from ornament. Processes unevenly scattered and occasionally aligned, presumably along parasutures, usually more closely together and larger in antapical region. Processes wartlike, conical or tubiform, 1-4 μm high, with rounded, pointed, or bifid tips.
Archaeopyle apical, large, margin zigzag indicating 6 precingular paraplates. Operculum free.
A paracingulum is often faintly and partly indicated as a single or double fold of the cyst wall in the equatorial region.
A parasulcus is not outlined.
Dimensions:
Apical diameter (4 entire specimens) 86-100 μm; diameter of 12 dehisced specimens 64-90 μm; maximum width 77-102 μm.
Affinities:
This species is assigned to Cyclonephelium on account of its apical archaeopyle and restricted process distribution. It differs from most species of the genus by its large dimensions, asymmetrical outline with prominent antapical bulges, and the sparse, tiny processes (Fig. 6c). In outline it resembles Canningia but it differs from that genus by the uneven, restricted process distribution. Canningia hirtella (Alberti) Millioud 1969 has a shorter epicyst and longer spinules.