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Alisogymnium evittii
From Fensome et al., 2019:
Alisogymnium evittii, (Boltenhagen, 1977, p.66–67, pl.8, figs.9a–c,10–11) Lentin and Vozzhennikova, 1990, p.28.
Holotype: Boltenhagen, 1977, pl.8, figs.9a–c; Lentin and Vozzhennikova, 1990, Appendix A, fig.33.
Originally Dinogymnium, subsequently (and now) Alisogymnium.
Age: Senonian.
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Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium evittii nov. sp.
DIAGNOSIS
Punctate theca, formed by a conical epitheca and a hemispherical hypotheca; ribs only on the epitheca and irregular; deep circular cingulate, sulcus on the hypotheca; apical archaeopyle.
DESCRIPTION
The small theca of this species has a peculiar shape: the epitheca is conical, ending in an acuminate apex, the hypotheca is subhemispherical, with a flat antapex. The irregular, slightly undulating ribs are located on the epitheca and disappear below the apex. Their number is variable and is estimated to be between 10 and 20 depending on the specimen considered. The hypotheca is devoid of ribs but is generally affected by a few disordered folds. The wall of the theca at 320x magnification is smooth or weakly punctuated. At 800x magnification, a more or less accentuated punctuation appears, which would be due to inframicroreticulation. A deep circular cingulum divides the theca into two unequal parts, the epitheca being the smaller. The cingulum coefficient (CI), based on the measurement of 5 specimens, is between 40 and 48 and on average is equal to 45. The two edges of the suicus overlap and form a large fold on the hypotheca extending to the antapex. It is only near the cingulum that this fold opens and its edges graft onto the cingulum. On the epitheca, the sucus extends into a hernicircular notch extending beyond the anterior edge of the cingulum. The apical archaeopyle appears as a wedge-shaped notch.
OBSERVATIONS
This species is common, but generally deformed. Few specimens lend themselves to correct measurements.
DIMENSIONS
Holotype: theca L = 34 μ; I = 22 μ
cingulum I = 2 - 3 μ
Paratypes: theca L = 37 μ and 27 μ; L = 20-27μ and 25-24 μ
Cingulum L = 5 μ and 3 μ
2 other specimens:
Theca L = 34 μ and 36 μ; I = 25 μ and 21-25 μ
NOTE: The maximum width of the theca is taken either at the level of the cingulum or separately on the epitheca and hypotheca.
COMPARISON
The described species bears a strong resemblance to Dinogymnium (Gymnodinium) sphaerocephalum VOZZH. 1967 (p. 48, PI. 11, Fig. 5) in its subhemispherical hypotheca and the absence of ribs on the latter in var. laevis. The main difference lies in the position of the cingulum, the coefficient of which would be around 67-80 according to the figures given by T.F. VOZZHENNIKOVA for his type species. Therefore, the epitheca is clearly larger than the hypotheca (1), otherwise this phenomenon is reversed compared to the Gabonese species.
Furthermore, the position of the sulcus in the Siberian species is not obvious. Furthermore, Dinogymnium (Gymnodinium) sp. 6 EV. 1967a (PI. I, Fig. P) appears to be identical to the Gabonese species.
Stratigraphic and Geographic Position
Upper Cretaceous: Senonian; Gabon (Port-Gentil, Feman-Vaz).
Alisogymnium evittii, (Boltenhagen, 1977, p.66–67, pl.8, figs.9a–c,10–11) Lentin and Vozzhennikova, 1990, p.28.
Holotype: Boltenhagen, 1977, pl.8, figs.9a–c; Lentin and Vozzhennikova, 1990, Appendix A, fig.33.
Originally Dinogymnium, subsequently (and now) Alisogymnium.
Age: Senonian.
---------------------------------------------------------------------------------------------------
Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium evittii nov. sp.
DIAGNOSIS
Punctate theca, formed by a conical epitheca and a hemispherical hypotheca; ribs only on the epitheca and irregular; deep circular cingulate, sulcus on the hypotheca; apical archaeopyle.
DESCRIPTION
The small theca of this species has a peculiar shape: the epitheca is conical, ending in an acuminate apex, the hypotheca is subhemispherical, with a flat antapex. The irregular, slightly undulating ribs are located on the epitheca and disappear below the apex. Their number is variable and is estimated to be between 10 and 20 depending on the specimen considered. The hypotheca is devoid of ribs but is generally affected by a few disordered folds. The wall of the theca at 320x magnification is smooth or weakly punctuated. At 800x magnification, a more or less accentuated punctuation appears, which would be due to inframicroreticulation. A deep circular cingulum divides the theca into two unequal parts, the epitheca being the smaller. The cingulum coefficient (CI), based on the measurement of 5 specimens, is between 40 and 48 and on average is equal to 45. The two edges of the suicus overlap and form a large fold on the hypotheca extending to the antapex. It is only near the cingulum that this fold opens and its edges graft onto the cingulum. On the epitheca, the sucus extends into a hernicircular notch extending beyond the anterior edge of the cingulum. The apical archaeopyle appears as a wedge-shaped notch.
OBSERVATIONS
This species is common, but generally deformed. Few specimens lend themselves to correct measurements.
DIMENSIONS
Holotype: theca L = 34 μ; I = 22 μ
cingulum I = 2 - 3 μ
Paratypes: theca L = 37 μ and 27 μ; L = 20-27μ and 25-24 μ
Cingulum L = 5 μ and 3 μ
2 other specimens:
Theca L = 34 μ and 36 μ; I = 25 μ and 21-25 μ
NOTE: The maximum width of the theca is taken either at the level of the cingulum or separately on the epitheca and hypotheca.
COMPARISON
The described species bears a strong resemblance to Dinogymnium (Gymnodinium) sphaerocephalum VOZZH. 1967 (p. 48, PI. 11, Fig. 5) in its subhemispherical hypotheca and the absence of ribs on the latter in var. laevis. The main difference lies in the position of the cingulum, the coefficient of which would be around 67-80 according to the figures given by T.F. VOZZHENNIKOVA for his type species. Therefore, the epitheca is clearly larger than the hypotheca (1), otherwise this phenomenon is reversed compared to the Gabonese species.
Furthermore, the position of the sulcus in the Siberian species is not obvious. Furthermore, Dinogymnium (Gymnodinium) sp. 6 EV. 1967a (PI. I, Fig. P) appears to be identical to the Gabonese species.
Stratigraphic and Geographic Position
Upper Cretaceous: Senonian; Gabon (Port-Gentil, Feman-Vaz).