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Alisogymnium downiei
From Fensome et al., 2019:
Alisogymnium downiei, (Boltenhagen, 1977, p.77–78, pl.11, figs.8a–c,9a–b,10) Lentin and Vozzhennikova, 1990, p.28.
Holotype: Boltenhagen, 1977, pl.11, figs.8a–c; Lentin and Vozzhennikova, 1990, Appendix A, fig.36.
Originally Dinogymnium, subsequently (and now) Alisogymnium.
Age: Campanian–Maastrichtian.
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Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium downiei nov. sp.
DIAGNOSIS
Small, globose theca, smooth or punctate, without ribs, epitheca smaller than hypotheca, both subhemispherical, circular cingulum shifted towards the apex. Sulcus on half of the hypotheca; apical archaeopyle.
DESCRIPTION
This small, globose species is characterized by the absence of ribs. The thin membrane (+ or - 0.5) of the theca is almost smooth or punctate; this punctuation at 800x magnification appears more like an inframicroperforation. The prominent circular cingulum divides the theca into two unequal parts, but of a similar shape, close to a hemisphere. The epitheca is smaller than the hypotheca. The sulcus is located on half of the hypotheca. The apical archaeopyle is typical of the genus Dinogymnium.
OBSERVATIONS
This species is not rare. However, the thin theca membrane is generally folded, so that the specimens observed are mostly deformed and often difficult to recognize. Turgid specimens are exceptional.
DIMENSIONS
Holotype: theca L x W = 31 x 28 μ
cingulum L = 4 - 6 μ
coef. (CI) = 42
Paratypes: theca L x W = 31 x 27 μ; 37 x 38 μ
cingulum coef. (CI) = 45 and 43
NOTE: Since the paratypes are compressed, the width of the cingulum cannot be measured.
COMPARISON
From a distance, the species described resembles D. avellana LEJ.-CARP. 1951 (p. B.309, Fig. 3) in its form. It is distinguished by the complete absence of ribs. Furthermore, G. KIESER in 1967 represents Dinogymnium (Gymnodinium) sp. (P.I. IV, Fig. II), which appears to be identical to the Gabonese species.
Stratigraphic and Geographic Position
Upper Cretaceous: Campanian, Maastrichtian, Gabon (Port-Gentil and Fernan-Vaz).
Alisogymnium downiei, (Boltenhagen, 1977, p.77–78, pl.11, figs.8a–c,9a–b,10) Lentin and Vozzhennikova, 1990, p.28.
Holotype: Boltenhagen, 1977, pl.11, figs.8a–c; Lentin and Vozzhennikova, 1990, Appendix A, fig.36.
Originally Dinogymnium, subsequently (and now) Alisogymnium.
Age: Campanian–Maastrichtian.
---------------------------------------------------------------------------------------------------
Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium downiei nov. sp.
DIAGNOSIS
Small, globose theca, smooth or punctate, without ribs, epitheca smaller than hypotheca, both subhemispherical, circular cingulum shifted towards the apex. Sulcus on half of the hypotheca; apical archaeopyle.
DESCRIPTION
This small, globose species is characterized by the absence of ribs. The thin membrane (+ or - 0.5) of the theca is almost smooth or punctate; this punctuation at 800x magnification appears more like an inframicroperforation. The prominent circular cingulum divides the theca into two unequal parts, but of a similar shape, close to a hemisphere. The epitheca is smaller than the hypotheca. The sulcus is located on half of the hypotheca. The apical archaeopyle is typical of the genus Dinogymnium.
OBSERVATIONS
This species is not rare. However, the thin theca membrane is generally folded, so that the specimens observed are mostly deformed and often difficult to recognize. Turgid specimens are exceptional.
DIMENSIONS
Holotype: theca L x W = 31 x 28 μ
cingulum L = 4 - 6 μ
coef. (CI) = 42
Paratypes: theca L x W = 31 x 27 μ; 37 x 38 μ
cingulum coef. (CI) = 45 and 43
NOTE: Since the paratypes are compressed, the width of the cingulum cannot be measured.
COMPARISON
From a distance, the species described resembles D. avellana LEJ.-CARP. 1951 (p. B.309, Fig. 3) in its form. It is distinguished by the complete absence of ribs. Furthermore, G. KIESER in 1967 represents Dinogymnium (Gymnodinium) sp. (P.I. IV, Fig. II), which appears to be identical to the Gabonese species.
Stratigraphic and Geographic Position
Upper Cretaceous: Campanian, Maastrichtian, Gabon (Port-Gentil and Fernan-Vaz).