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Rimosicysta aspera
Rimosicysta aspera Marshall 1989
Holotype. Marshall 1989: Plate 3, figs. 7, 8.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall 1989, p. 44, 46
Middorsal bulge weak to pronounced, usually flattened to produce a lateral fold. Dorsoventral outline equidimensional or longitudinally elongate. Apical margin truncated, outline irregular. Cysts widest near equator where lateral margins are extended to form subrectangular struc- tures. Hypocystal and epicystal flanks nearly straight to convex or marked near their midlength by a pronounced concavity with a flattened base. Antapical margin convex or bears two subrectangular extensions with flattened distal margins, extensions separated by a narrow concavity. Autophragm thins markedly along apical margin and within concavities on late ral margins, and wall frequently split apart parallel to cyst outline in these areas. Autophragm elsewhere around periphery 0.3-0.4 µm thick, surface smooth and frequently strongly crumpled. Periphery of cyst usually bears a row of hollow projections with extremely variable length, shape, and distribution. Projections rounded to pointed, up to S ,um long, and where concentrated in groups, produce a serrated outline. Projections most pronounced at equator and on epicyst, not evident within concavities on lateral margins. Midventral surface bears a prominent longitudinal fold usually extending along entire length of cyst. Fold highest near equator and on hypocyst. Crest of fold across dorsal surface and rarely longitudinal fold along midventral surface may bear a row of projections similar to those around the periphery of cyst, but are considerably reduced on longitudinal fold. Possible paracingulum defined rarely by two parallel ridges extending across crest of lateral fold on middorsal surface. Ridges bear the same type of projections as those occurring around periphery of cyst.
Size. Autocyst length 75(95)130 µm, width 66(86)112 µm; 23 specimens measured.
Comparison. Marshall 1989, p. 44, 46
The extremely variable outline of this form is shown in Text-Figure 11. Most specimens examined have at least some indication of the rounded to pointed projections around the periphery of the cyst. The rare variants lacking these elements resemble Rimosicysta kipperii sp. nov., but differ in having a more angular outline, especially surrounding the equatorial protrusions on the lateral margins. This species further resembles R. kipperii in often having a pronounced longitudinal fold on the middle of the ventral surface.
Occurrence. Cook Cruise sample C4/87 21DDa; Sunfish-l, 2483.7 m.
Holotype. Marshall 1989: Plate 3, figs. 7, 8.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description. Marshall 1989, p. 44, 46
Middorsal bulge weak to pronounced, usually flattened to produce a lateral fold. Dorsoventral outline equidimensional or longitudinally elongate. Apical margin truncated, outline irregular. Cysts widest near equator where lateral margins are extended to form subrectangular struc- tures. Hypocystal and epicystal flanks nearly straight to convex or marked near their midlength by a pronounced concavity with a flattened base. Antapical margin convex or bears two subrectangular extensions with flattened distal margins, extensions separated by a narrow concavity. Autophragm thins markedly along apical margin and within concavities on late ral margins, and wall frequently split apart parallel to cyst outline in these areas. Autophragm elsewhere around periphery 0.3-0.4 µm thick, surface smooth and frequently strongly crumpled. Periphery of cyst usually bears a row of hollow projections with extremely variable length, shape, and distribution. Projections rounded to pointed, up to S ,um long, and where concentrated in groups, produce a serrated outline. Projections most pronounced at equator and on epicyst, not evident within concavities on lateral margins. Midventral surface bears a prominent longitudinal fold usually extending along entire length of cyst. Fold highest near equator and on hypocyst. Crest of fold across dorsal surface and rarely longitudinal fold along midventral surface may bear a row of projections similar to those around the periphery of cyst, but are considerably reduced on longitudinal fold. Possible paracingulum defined rarely by two parallel ridges extending across crest of lateral fold on middorsal surface. Ridges bear the same type of projections as those occurring around periphery of cyst.
Size. Autocyst length 75(95)130 µm, width 66(86)112 µm; 23 specimens measured.
Comparison. Marshall 1989, p. 44, 46
The extremely variable outline of this form is shown in Text-Figure 11. Most specimens examined have at least some indication of the rounded to pointed projections around the periphery of the cyst. The rare variants lacking these elements resemble Rimosicysta kipperii sp. nov., but differ in having a more angular outline, especially surrounding the equatorial protrusions on the lateral margins. This species further resembles R. kipperii in often having a pronounced longitudinal fold on the middle of the ventral surface.
Occurrence. Cook Cruise sample C4/87 21DDa; Sunfish-l, 2483.7 m.