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Impagidinium striatum
Impagidinium striatum (Clarke and Verdier, 1967) Stover and Evitt, 1978
NOW Dimidium. Originally Gonyaulacysta, subsequently Leptodinium, thirdly Impagidinium, fourthly Pterodinium, fifthly (and now) Dimidium.
Holotype: Clarke and Verdier, 1967, pl.4, figs.11-13; Jan du Chêne, 1986, pl.88, figs.9-11
Locus typicus: Isle of Wight, Culver Cliff, England
Stratum typicum: Santonian
Original diagnosis: Clarke and Verdier, 1967, p.31: Gonyaulacysta striata
A species of Gonyaulacysta having no apical horn but possessing thin, often striate ledges.
Description: Clarke and Verdier, 1067, p.31: Gonyaulacysta striata
Outline circular or oval without an apical horn. Tabulation is distinct and conforms to the Gonyaulacysta pattern. Girdle strongly displaced, sometimes more than two girdle widths. Cingular plates present. Longitudinal furrow straight. Plates smooth, bordered by ledges up to 5 µ high with a non-protruding support at their junctions. These ledges are thin, often transparent and generally vertically striate. The precingular archaeopyle is not an obvious feature of most specimens.
Dimensions: Holotype: Overall length 66 µm, overall breadth 55 µm, height of ledges (max.) 11 µm, width of girdle 5 µm. Range: Overall length 40-66 µm, overall breadth 40-55 µm, height of ledges (max.) 4-11 µm, width of girdle 4-6 µm.
Affinities:
Clarke and Verdier, 1967, p.31: Gonyaulacysta striata
G. striata differs from G. tenuiceras Eisenack in the absence of an apical horn and sculpture on the plates. Gonyaulax freaki Sarjeant differs in having only five postcingular plates and smooth or perforate ledges. G. striata differs from G. ambigua (Defl.) in having higher ledges and from G. pachyderma (Defl.) in the absence of denticulate ledges.
NOW Dimidium. Originally Gonyaulacysta, subsequently Leptodinium, thirdly Impagidinium, fourthly Pterodinium, fifthly (and now) Dimidium.
Holotype: Clarke and Verdier, 1967, pl.4, figs.11-13; Jan du Chêne, 1986, pl.88, figs.9-11
Locus typicus: Isle of Wight, Culver Cliff, England
Stratum typicum: Santonian
Original diagnosis: Clarke and Verdier, 1967, p.31: Gonyaulacysta striata
A species of Gonyaulacysta having no apical horn but possessing thin, often striate ledges.
Description: Clarke and Verdier, 1067, p.31: Gonyaulacysta striata
Outline circular or oval without an apical horn. Tabulation is distinct and conforms to the Gonyaulacysta pattern. Girdle strongly displaced, sometimes more than two girdle widths. Cingular plates present. Longitudinal furrow straight. Plates smooth, bordered by ledges up to 5 µ high with a non-protruding support at their junctions. These ledges are thin, often transparent and generally vertically striate. The precingular archaeopyle is not an obvious feature of most specimens.
Dimensions: Holotype: Overall length 66 µm, overall breadth 55 µm, height of ledges (max.) 11 µm, width of girdle 5 µm. Range: Overall length 40-66 µm, overall breadth 40-55 µm, height of ledges (max.) 4-11 µm, width of girdle 4-6 µm.
Affinities:
Clarke and Verdier, 1967, p.31: Gonyaulacysta striata
G. striata differs from G. tenuiceras Eisenack in the absence of an apical horn and sculpture on the plates. Gonyaulax freaki Sarjeant differs in having only five postcingular plates and smooth or perforate ledges. G. striata differs from G. ambigua (Defl.) in having higher ledges and from G. pachyderma (Defl.) in the absence of denticulate ledges.