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Alterbidinium bicellulum
From Fensome et al., 2019:
Alterbidinium? bicellulum, (Islam, 1983b, p.335–336, pl.1, figs.6–7) Lentin and Williams, 1985, p.14.
Holotype: Islam, 1983b, pl.1, fig.6.
Originally Alterbia (generic name illegitimate), subsequently (and now) Alterbidinium?.
Questionable assignment: Lentin and Williams (1985, p.14).
Age: Middle Eocene.
Locus typicus: Hampshire Basin, S England
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Original description as Alterbia? bicellula: [Islam, 1983, p. 336]:
Diagnosis:
Pericyst dorsoventrally compressed peridinioid with short, conical apical horn commonly having rounded tip, broadening proximally to merge to epipericyst ambitus, and two unequal antapical horns, the left broad-based and conical with pointed tip and more or less equal in length to the apical horn, the right reduced, with a rounded tip; endocyst subspherical and oblate; proximate and bicavate; both phragma thin, chagrinate and sometimes wrinkled; folds in periphragm always defining paracingulum, which may be slightly helicoidal and sunken; parasulcus sometimes indicated by slight depression;
archeopyle intercalary type lll with standard hexa style, operculum attached;
epipericoel with or without communication to exterior.
Dimensions:
Holotype: pericyst 54 x 47 µm, endocyst 36 x 46 µm, archeopyle index 0.49.
Range: pericyst length 60(54)48 µm, breadth 54(49)43 µm; endocyst length 45(39)31 µm, breadth 53(47)42 µm; archeopyle index 0.60(0.53)0.49 (9 specimens). Specimens measured: 13.
Discussion:
The generic assignment of the species is based on general morphology, but questioned because the epipericoel is not always communicative to the exterior, and its degree of cavation and the archeopyle index do not match those prescribed for the genus. The degree of cavation and the archeopyle index of this species also do not match those of other peridinioid genera that are differentiated on the basis of these features by Lentin and Williams (1976). These features serve to differentiate it from other species of the genus.
The problem was discussed by Stover and Evitt (1978) who met with "greatest difficulties" in drawing generic limits of their Peridiniacean genera of Subcategory 3D which includes Alterbia. They also noted that species attributed to the genera of this subcategory "exhibit shades of difference and degree of morphologic overlap that leave many uncertainties about what criteria should be applied." In view of these difficulties, tentative allocation of the species to Alterbia is preferred to creating a new genus to accommodate it.
Alterbidinium? bicellulum, (Islam, 1983b, p.335–336, pl.1, figs.6–7) Lentin and Williams, 1985, p.14.
Holotype: Islam, 1983b, pl.1, fig.6.
Originally Alterbia (generic name illegitimate), subsequently (and now) Alterbidinium?.
Questionable assignment: Lentin and Williams (1985, p.14).
Age: Middle Eocene.
Locus typicus: Hampshire Basin, S England
---------------------------------------------------------------------------------------------------
Original description as Alterbia? bicellula: [Islam, 1983, p. 336]:
Diagnosis:
Pericyst dorsoventrally compressed peridinioid with short, conical apical horn commonly having rounded tip, broadening proximally to merge to epipericyst ambitus, and two unequal antapical horns, the left broad-based and conical with pointed tip and more or less equal in length to the apical horn, the right reduced, with a rounded tip; endocyst subspherical and oblate; proximate and bicavate; both phragma thin, chagrinate and sometimes wrinkled; folds in periphragm always defining paracingulum, which may be slightly helicoidal and sunken; parasulcus sometimes indicated by slight depression;
archeopyle intercalary type lll with standard hexa style, operculum attached;
epipericoel with or without communication to exterior.
Dimensions:
Holotype: pericyst 54 x 47 µm, endocyst 36 x 46 µm, archeopyle index 0.49.
Range: pericyst length 60(54)48 µm, breadth 54(49)43 µm; endocyst length 45(39)31 µm, breadth 53(47)42 µm; archeopyle index 0.60(0.53)0.49 (9 specimens). Specimens measured: 13.
Discussion:
The generic assignment of the species is based on general morphology, but questioned because the epipericoel is not always communicative to the exterior, and its degree of cavation and the archeopyle index do not match those prescribed for the genus. The degree of cavation and the archeopyle index of this species also do not match those of other peridinioid genera that are differentiated on the basis of these features by Lentin and Williams (1976). These features serve to differentiate it from other species of the genus.
The problem was discussed by Stover and Evitt (1978) who met with "greatest difficulties" in drawing generic limits of their Peridiniacean genera of Subcategory 3D which includes Alterbia. They also noted that species attributed to the genera of this subcategory "exhibit shades of difference and degree of morphologic overlap that leave many uncertainties about what criteria should be applied." In view of these difficulties, tentative allocation of the species to Alterbia is preferred to creating a new genus to accommodate it.