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Amphigymnium rigaudiae
From Fensome et al., 2019:
Amphigymnium rigaudiae, (Boltenhagen, 1977, p.73, pl.11, figs.1a–b,2–4) Lentin and Vozzhennikova, 1990, p.30.
Holotype: Boltenhagen, 1977, pl.11, figs.1a–b; Lentin and Vozzhennikova, 1990, Appendix A, fig.39.
Originally Dinogymnium, subsequently (and now) Amphigymnium.
Age: Campanian–Maastrichtian.
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Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium rigaudae nov. sp.
Pointe-Clairette Series, Campanian; Port-Gentil (Gabon, Equatorial Africa).
DIAGNOSIS
Finger-shaped theca barely constricted by a circular cingulum shifted towards the apex; epitheca narrower and smaller than the hypotheca; conical-rounded apex, ogival antapex, a small archaeopyle on the apical pole.
DESCRIPTION
The theca of our specimens has a characteristic shape, close to that of a finger. The very slight circular cingulum (or traces thereof) divides the theca into an epitheca and a hypotheca of similar shape, but the former is shorter and slightly narrower.
The apex is conical and rounded; the antapex has an ogival shape. The fairly thick membrane is smooth. At 800x magnification, however, some possible punctuation marks appear. On the apex of one specimen, a very small archaeopyle is observed (opening 1-2 μ), with the operculum detaching.
DIMENSIONS
Holotype: theca: L x l = 52 x 15μ
cingulum: coeff. (CI) = 42
3 figured paratypes:
theca: L x l = 47 x 13μ, 57 x 15μ, 56 x 14μ
cingulum: coeff. (CI) = 42, 43, 44
COMPARISON
In its general appearance, the described species bears resemblance to Dinogymnium {Gymnodinium } digitus DEFL. 1936 (p. 18, PI. 2, Fig. 4-5). It is distinguished by its reduced and non-depressed cingulum, the absence of a sulcus, and the smooth, non-punctate (microperforated?) and striated membrane. In addition, the shape of the theca is somewhat different.
Stratigraphic and geographic position
Upper Cretaceous: Campanian-Maastrichtian; Gabon (Port-Gentil and Fernan-Vaz).
Amphigymnium rigaudiae, (Boltenhagen, 1977, p.73, pl.11, figs.1a–b,2–4) Lentin and Vozzhennikova, 1990, p.30.
Holotype: Boltenhagen, 1977, pl.11, figs.1a–b; Lentin and Vozzhennikova, 1990, Appendix A, fig.39.
Originally Dinogymnium, subsequently (and now) Amphigymnium.
Age: Campanian–Maastrichtian.
---------------------------------------------------------------------------------------------------
Original description: [Boltenhagen, 1977] (translated from French):
Dinogymnium rigaudae nov. sp.
Pointe-Clairette Series, Campanian; Port-Gentil (Gabon, Equatorial Africa).
DIAGNOSIS
Finger-shaped theca barely constricted by a circular cingulum shifted towards the apex; epitheca narrower and smaller than the hypotheca; conical-rounded apex, ogival antapex, a small archaeopyle on the apical pole.
DESCRIPTION
The theca of our specimens has a characteristic shape, close to that of a finger. The very slight circular cingulum (or traces thereof) divides the theca into an epitheca and a hypotheca of similar shape, but the former is shorter and slightly narrower.
The apex is conical and rounded; the antapex has an ogival shape. The fairly thick membrane is smooth. At 800x magnification, however, some possible punctuation marks appear. On the apex of one specimen, a very small archaeopyle is observed (opening 1-2 μ), with the operculum detaching.
DIMENSIONS
Holotype: theca: L x l = 52 x 15μ
cingulum: coeff. (CI) = 42
3 figured paratypes:
theca: L x l = 47 x 13μ, 57 x 15μ, 56 x 14μ
cingulum: coeff. (CI) = 42, 43, 44
COMPARISON
In its general appearance, the described species bears resemblance to Dinogymnium {Gymnodinium } digitus DEFL. 1936 (p. 18, PI. 2, Fig. 4-5). It is distinguished by its reduced and non-depressed cingulum, the absence of a sulcus, and the smooth, non-punctate (microperforated?) and striated membrane. In addition, the shape of the theca is somewhat different.
Stratigraphic and geographic position
Upper Cretaceous: Campanian-Maastrichtian; Gabon (Port-Gentil and Fernan-Vaz).