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Rhombodinium elongatum
Rhombodinium elongatum He Chengquan, 1991
Holotype: He Chengquan, 1991, pl.41, fig.1
Age: Middle Eocene
Description from He Chengquan, 1991, translated by Suning Hou, 07-01-2019
Description: The cyst is dorsal-ventral flattened, outline kite-shaped or elongated pentagon. The upper cyst is smaller than the lower cyst, triangular, side concave, a developed apical horn extending at the top, length 17.5-35μm, the top blunt circle. The hypocyst is inverted trapezoid with two antapical horns, usually markedly unequal in length, tapering distally, end blunt conical or rod-shaped, left antapical horn length 20-44μm, right length 10-25μm, 2 lateral horns are significant, length 16.5-32.5μm, tapering distally, the end open or concave. The ends of apical and lateral horns are simple, or granular- ridge like, or with short rod spines (length 1-2μm). The cingulum is at the equatorial position, clearly through the 2 lateral horns. The outer wall surface (except for the horn end) is smooth or fine-grained, with a smooth contour. The inner body is regular oval round and more or less extends toward the lateral horns, with a smooth or finely grained surface; It is usually separated from the outer wall with a narrow outer cavity, in addition to the horns, the outer cavity is 0 - 5μm wide at the cyst side. Archeopyle intercalary, outline clear, round trapezoid. Operculum is completely separated, usually preserved in situ or attached along the archeopyle side. Cyst length 130-185μm, width 97.5-150μm, inner body length 87 a 105μm, width 72-97 5μm (measured 14 ); The length of the holotype is 155μm, width 125μm, inner body length 95μm, width 81μm, apical horn length 25μm, length of left antapical horn is 40μm, length of right antapical horn is 19μm, lateral horn length 22μm.
Comparison: This species is distinguished from Rhombodinium sinense and R. elegans, respectively, by the elongation of the cyst and the pronounced unequal length of the two antapical horns. Based on the end of the lateral horns with or without short-rod shape processes, this species is divided into 2 subspecies: R. elongatum subsp. elongatum and R. elongatum subsp. spinale.
Holotype: He Chengquan, 1991, pl.41, fig.1
Age: Middle Eocene
Description from He Chengquan, 1991, translated by Suning Hou, 07-01-2019
Description: The cyst is dorsal-ventral flattened, outline kite-shaped or elongated pentagon. The upper cyst is smaller than the lower cyst, triangular, side concave, a developed apical horn extending at the top, length 17.5-35μm, the top blunt circle. The hypocyst is inverted trapezoid with two antapical horns, usually markedly unequal in length, tapering distally, end blunt conical or rod-shaped, left antapical horn length 20-44μm, right length 10-25μm, 2 lateral horns are significant, length 16.5-32.5μm, tapering distally, the end open or concave. The ends of apical and lateral horns are simple, or granular- ridge like, or with short rod spines (length 1-2μm). The cingulum is at the equatorial position, clearly through the 2 lateral horns. The outer wall surface (except for the horn end) is smooth or fine-grained, with a smooth contour. The inner body is regular oval round and more or less extends toward the lateral horns, with a smooth or finely grained surface; It is usually separated from the outer wall with a narrow outer cavity, in addition to the horns, the outer cavity is 0 - 5μm wide at the cyst side. Archeopyle intercalary, outline clear, round trapezoid. Operculum is completely separated, usually preserved in situ or attached along the archeopyle side. Cyst length 130-185μm, width 97.5-150μm, inner body length 87 a 105μm, width 72-97 5μm (measured 14 ); The length of the holotype is 155μm, width 125μm, inner body length 95μm, width 81μm, apical horn length 25μm, length of left antapical horn is 40μm, length of right antapical horn is 19μm, lateral horn length 22μm.
Comparison: This species is distinguished from Rhombodinium sinense and R. elegans, respectively, by the elongation of the cyst and the pronounced unequal length of the two antapical horns. Based on the end of the lateral horns with or without short-rod shape processes, this species is divided into 2 subspecies: R. elongatum subsp. elongatum and R. elongatum subsp. spinale.