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Gonyaulacysta tenuicornuta
Gonyaulacysta tenuicornuta (Cookson and Eisenack, 1962) Sarjeant, 1969
Now Leptodinium?. Originally Leptodinium, subsequently Gonyaulacysta, thirdly (and now) Leptodinium?.
Holotype: Cookson and Eisenack, 1962, pl.3, figs.12-13
Locus typicus: Australia, Perth Basin, Regan"s Ford on Moore River
Stratum typicum: Albian
Original diagnosis: Cookson and Eisenack, 1962, p.487: Leptodinium? tenuicornutum
Shell small, broadly oval, divided by a relatively broad, strongly helicoid girdle with low borders into a somewhat conical epitheca and a nearly hemispherical hypotheca. Epitheca provided with a hollow membranous horn. Longitudinal furrow rather broad. Plates finely dotted, bordered bylow membranous ledges which are more pronounced in the median plane, especially at the antapex. Pylome formed by the detachment of plate 3". Tabulation: 3"?, 6", 5""", 1"""".
Dimensions: Holotype: 55 Ám long, 48 Ám broad.
Affinities:
Cookson and Eisenack, 1962, p.487: Leptodinium ?tenuicornutum
The single specimen agrees with Klement" s genus Leptodinium in having only five postequatorial plates and an undivided longitudinal furrow which extends from plate 1" to plate 1"""" . However, it differs from Leptodinium in having a membranous horn and higher borders to the plates, especially those of the antapical region, than allowed for in the generic description. Also plate 1p seems to be missing.
Since the closely related genus Gonyaulax contains species both with and without apical horns, there seems no reason why the genus Leptodinium should not be enlarged to include horned forms. However, with only one available specimen, this idea cannot, at present, be prosecuted further.
Now Leptodinium?. Originally Leptodinium, subsequently Gonyaulacysta, thirdly (and now) Leptodinium?.
Holotype: Cookson and Eisenack, 1962, pl.3, figs.12-13
Locus typicus: Australia, Perth Basin, Regan"s Ford on Moore River
Stratum typicum: Albian
Original diagnosis: Cookson and Eisenack, 1962, p.487: Leptodinium? tenuicornutum
Shell small, broadly oval, divided by a relatively broad, strongly helicoid girdle with low borders into a somewhat conical epitheca and a nearly hemispherical hypotheca. Epitheca provided with a hollow membranous horn. Longitudinal furrow rather broad. Plates finely dotted, bordered bylow membranous ledges which are more pronounced in the median plane, especially at the antapex. Pylome formed by the detachment of plate 3". Tabulation: 3"?, 6", 5""", 1"""".
Dimensions: Holotype: 55 Ám long, 48 Ám broad.
Affinities:
Cookson and Eisenack, 1962, p.487: Leptodinium ?tenuicornutum
The single specimen agrees with Klement" s genus Leptodinium in having only five postequatorial plates and an undivided longitudinal furrow which extends from plate 1" to plate 1"""" . However, it differs from Leptodinium in having a membranous horn and higher borders to the plates, especially those of the antapical region, than allowed for in the generic description. Also plate 1p seems to be missing.
Since the closely related genus Gonyaulax contains species both with and without apical horns, there seems no reason why the genus Leptodinium should not be enlarged to include horned forms. However, with only one available specimen, this idea cannot, at present, be prosecuted further.