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Rimosicysta cucullata
Rimosicysta cucullata Marshall 1989
Holotype. Marshall 1989: Plate 4, figs. 9-11.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description: Marshall 1989, p. 46, 48
Cysts with a pronounced middorsal bulge; dorsoventral outline generally equidimensional. Epicystal flanks convex, apical margin also convex, but slightly flattened relative to surrounding margins. Curvature of epicystal flanks extends below equator and terminates with two narrowly subconical horns pointing antapically. Horns taper distally with narrowly rounded tips. Each horn separated from antapical margin by a pronounced concavity. Antapical margin modified by two elongate projections of similar shape and length. Antapical projections markedly flared towards tips, distal margins flattened; separated by a concave margin or two concavities divided by a medial peak. Autophragm surface smooth, strongly crumpled; usually 0.3-0.4 µm thick around periphery of cyst and appears to thicken middorsally and midventrally on some specimens. Autophragm thins markedly and is frequently split apart parallel to cyst outline along apical margin and along concavities beneath lateral horns. Possible paracingulum defined on dorsal surface by two parallel, transverse, thickened, rounded ridges 3-4 µm apart. Ridges separated by a shallow groove; intersection of groove with lateral margins is marked by a rounded notch. Possible parasulcus marked on midventral surface by two subparallel, longitudinal lines of thickening or thickened ridges separated by a shallow groove, or by one or two pronounced folds. Folds often extend along much of the cyst length. On one variant with a longitudinal groove bordered by two ridges (Plate 4, figs. 7, 8; Text-Figure 12), outer edges of the ridges near midventral surface bordered by two circular depressions.
Size. Autocyst length 71(80)118 µm, width 72(82)125 µm; 24 specimens measured.
Comparison: Marshall 1989, p. 46, 48
The markedly convex outline of the epicyst and the pronounced, antapically directed lateral horns distinguish this taxon from other species. It has the clearest indications of a possible paracingulum and parasulcus of all species of the genus. The unusual depressions on either side of the possible parasulcus on the specimen in Plate 4, figs. 7, 8 are distinctive, but are of unknown significance.
Occurrence. Sunfish-l. 2482.7-2484.4 m.
Holotype. Marshall 1989: Plate 4, figs. 9-11.
Locus typicus: Gippsland Basin, Southeastern Australia
Stratum typicum: Late Cretaceous
Description: Marshall 1989, p. 46, 48
Cysts with a pronounced middorsal bulge; dorsoventral outline generally equidimensional. Epicystal flanks convex, apical margin also convex, but slightly flattened relative to surrounding margins. Curvature of epicystal flanks extends below equator and terminates with two narrowly subconical horns pointing antapically. Horns taper distally with narrowly rounded tips. Each horn separated from antapical margin by a pronounced concavity. Antapical margin modified by two elongate projections of similar shape and length. Antapical projections markedly flared towards tips, distal margins flattened; separated by a concave margin or two concavities divided by a medial peak. Autophragm surface smooth, strongly crumpled; usually 0.3-0.4 µm thick around periphery of cyst and appears to thicken middorsally and midventrally on some specimens. Autophragm thins markedly and is frequently split apart parallel to cyst outline along apical margin and along concavities beneath lateral horns. Possible paracingulum defined on dorsal surface by two parallel, transverse, thickened, rounded ridges 3-4 µm apart. Ridges separated by a shallow groove; intersection of groove with lateral margins is marked by a rounded notch. Possible parasulcus marked on midventral surface by two subparallel, longitudinal lines of thickening or thickened ridges separated by a shallow groove, or by one or two pronounced folds. Folds often extend along much of the cyst length. On one variant with a longitudinal groove bordered by two ridges (Plate 4, figs. 7, 8; Text-Figure 12), outer edges of the ridges near midventral surface bordered by two circular depressions.
Size. Autocyst length 71(80)118 µm, width 72(82)125 µm; 24 specimens measured.
Comparison: Marshall 1989, p. 46, 48
The markedly convex outline of the epicyst and the pronounced, antapically directed lateral horns distinguish this taxon from other species. It has the clearest indications of a possible paracingulum and parasulcus of all species of the genus. The unusual depressions on either side of the possible parasulcus on the specimen in Plate 4, figs. 7, 8 are distinctive, but are of unknown significance.
Occurrence. Sunfish-l. 2482.7-2484.4 m.