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Alterbia asymmetrica
Alterbia asymmetrica, (Wilson, 1967a, p. 62–63, figs.17–21), Lentin and Williams, 1976, p.48.
Combination illegitimate: the generic name Alterbia is illegitimate.
NOW Alterbidinium. Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly Senegalinium?, fourthly (and now) Alterbidinium, fifthly Magallanesium.
Holotype: Wilson, 1967a, figs.19–21.
Age: ?Eocene (erratic).
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Description:
Test bi-Iayered, dorso-ventrally flattened, angular, bilaterally asymmetric; margin often finely serrated in part. Inner layer differentiated into thin-walled smooth inner cyst of sub-angular or subcircular outline. Outer cyst smooth with very distinctive smooth keel-like folds or ridges roughly parallel to the test margin on both dorsal and ventral epithecae; a further two ridges. more centrally located. extend on the ventral surface from each antapical horn to the transverse girdle; a depressed area between the two ridges indicates a large longitudinal furrow. Spiral transverse girdle represented by a low smooth or finely serrated ridge on the dorsal surface. Apical horn relatively long (/= 14-22 μm). rectangular. blunt-ended; right antapical horn prominent. pointed (/=7-12 μm); left antapical horn very small (/=2-4 μm).
Archeopyle sub-hexagonal or hoof-shaped. intercalary. located on dorsal epitheca. Operculum hinged to test by posterior margin (Fig. 21). Atabulate.
Dimensions:
Holotype 1=80 μm. b=55 μm. dimensions of inner cyst (50X47) μm.
Range 1=50(84)99 μm. b=43(58)66 μm (9 specimens).
Discussion/Affinities:
Deflandrea ruymmetrica belongs to the group of asymmetric Deflandrea species possessing hinged archeopyle opercula. There is some similarity to D. ventriosa Alberti (Alberti. 1959). However. the surface ornamentation differs. A comparison of Deflandrea asymmetrica. D. macmurdoensis. and D. distincta is given below (see under discussion of D. distincta). D. ruymmetrica was recorded as Deflandrea spp. indet. in the preliminary species list of McIntyre and Wilson (1966. table 2). Deflandrea ruymmetrica is fairly common in the Minna Bluff assemblage. though rare in all Black Island samples.
Combination illegitimate: the generic name Alterbia is illegitimate.
NOW Alterbidinium. Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly Senegalinium?, fourthly (and now) Alterbidinium, fifthly Magallanesium.
Holotype: Wilson, 1967a, figs.19–21.
Age: ?Eocene (erratic).
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Description:
Test bi-Iayered, dorso-ventrally flattened, angular, bilaterally asymmetric; margin often finely serrated in part. Inner layer differentiated into thin-walled smooth inner cyst of sub-angular or subcircular outline. Outer cyst smooth with very distinctive smooth keel-like folds or ridges roughly parallel to the test margin on both dorsal and ventral epithecae; a further two ridges. more centrally located. extend on the ventral surface from each antapical horn to the transverse girdle; a depressed area between the two ridges indicates a large longitudinal furrow. Spiral transverse girdle represented by a low smooth or finely serrated ridge on the dorsal surface. Apical horn relatively long (/= 14-22 μm). rectangular. blunt-ended; right antapical horn prominent. pointed (/=7-12 μm); left antapical horn very small (/=2-4 μm).
Archeopyle sub-hexagonal or hoof-shaped. intercalary. located on dorsal epitheca. Operculum hinged to test by posterior margin (Fig. 21). Atabulate.
Dimensions:
Holotype 1=80 μm. b=55 μm. dimensions of inner cyst (50X47) μm.
Range 1=50(84)99 μm. b=43(58)66 μm (9 specimens).
Discussion/Affinities:
Deflandrea ruymmetrica belongs to the group of asymmetric Deflandrea species possessing hinged archeopyle opercula. There is some similarity to D. ventriosa Alberti (Alberti. 1959). However. the surface ornamentation differs. A comparison of Deflandrea asymmetrica. D. macmurdoensis. and D. distincta is given below (see under discussion of D. distincta). D. ruymmetrica was recorded as Deflandrea spp. indet. in the preliminary species list of McIntyre and Wilson (1966. table 2). Deflandrea ruymmetrica is fairly common in the Minna Bluff assemblage. though rare in all Black Island samples.