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Rimosicysta eversa
Rimosicysta eversa Marshall, 1989
Holotype. Plate 6, figs. 1-3.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall, 1989, p. 40, 42
Middorsal surface with a pronounced bulge that is often flattened to form a transverse fold. Ends of fold occasionally bifurcate near lateral margins. Lateral margins extended at equator to produce rounded bulges or subrectangular extensions with the midlength of each distal margin occasionally marked by a shallow, rounded notch. Lateral margins on either side of the equatorial extensions strongly convex. Apical and antapical margins flattened, often weakly convex, and each is bordered by two rounded bulges or subrectangular protrusions that are flattened distally. Antapical margin rarely marked by a weak medial peak. Autophragm frequently appears to thin towards periphery of cyst. Thinning most pronounced apically and antapically, and along concavities on either side of the equatorial extensions, and the autophragm can be split apart parallel to the cyst outline in these areas. Elsewhere around periphery, autophragm 0.2-0.4 µm thick. Cyst surface smooth, commonly bearing irregularly distributed, frequent to common, rounded grana up to 0.6 µm in maximum dimension. Midventral surface usually marked by one or two longitudinal folds which frequently extend over much of the cyst length. Folds most prominent equatorially and on hypocyst.
Size. Autocyst length 102(122)138 µm, width 66(84)102 µm; 11 specimens measured.
Discussion. Marshall, 1989, p. 40, 42
It is often difficult to distinguish the epicyst from the hypocyst because both have similar outlines. On occasional specimens, the longitudinal fold on the ventral surface intersects the antapical margin and this is marked by a small rounded peak. The longitudinal fold usually terminates before reaching the apical margin.
Comparison. Rimosicysta eversa sp. nov. differs from other species of the genus by its gently curved outline that is modified by rounded protrusions on the apical, antapical, and lateral margins.
Occurrence. Cook Cruise sample C4/87 21DDa.
Holotype. Plate 6, figs. 1-3.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall, 1989, p. 40, 42
Middorsal surface with a pronounced bulge that is often flattened to form a transverse fold. Ends of fold occasionally bifurcate near lateral margins. Lateral margins extended at equator to produce rounded bulges or subrectangular extensions with the midlength of each distal margin occasionally marked by a shallow, rounded notch. Lateral margins on either side of the equatorial extensions strongly convex. Apical and antapical margins flattened, often weakly convex, and each is bordered by two rounded bulges or subrectangular protrusions that are flattened distally. Antapical margin rarely marked by a weak medial peak. Autophragm frequently appears to thin towards periphery of cyst. Thinning most pronounced apically and antapically, and along concavities on either side of the equatorial extensions, and the autophragm can be split apart parallel to the cyst outline in these areas. Elsewhere around periphery, autophragm 0.2-0.4 µm thick. Cyst surface smooth, commonly bearing irregularly distributed, frequent to common, rounded grana up to 0.6 µm in maximum dimension. Midventral surface usually marked by one or two longitudinal folds which frequently extend over much of the cyst length. Folds most prominent equatorially and on hypocyst.
Size. Autocyst length 102(122)138 µm, width 66(84)102 µm; 11 specimens measured.
Discussion. Marshall, 1989, p. 40, 42
It is often difficult to distinguish the epicyst from the hypocyst because both have similar outlines. On occasional specimens, the longitudinal fold on the ventral surface intersects the antapical margin and this is marked by a small rounded peak. The longitudinal fold usually terminates before reaching the apical margin.
Comparison. Rimosicysta eversa sp. nov. differs from other species of the genus by its gently curved outline that is modified by rounded protrusions on the apical, antapical, and lateral margins.
Occurrence. Cook Cruise sample C4/87 21DDa.