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Planoperidinium gracile
Planoperidinium gracile De Coninck, 1986
Holotype: De Coninck, 1986, pl.8, fig.1-3
Locus typicus: Woensdrecht borehole, S Netherlands
Stratum typicum: Rupelian
Original diagnosis: De Coninck, 1986, p.18
The pericyst is dorsoventrally flattened. Its ambitus is peridinoid. The epicyst is generally a little longer than the hypocyst and has a more or less triangular outline. The apical horn is poorly developed and rounded. The cingular margins are marked on the ambitus by short protrusions between which the cingulum is represented by a shallow depression. Generally the cingulum and sulcus are invisible on the dorsal and ventral surfaces of the pericyst. The hypocyst is trapezium-shaped with two protruding antapical horns with a pointed, often flexuous tip. One of the antapical horns is a little longer than the other. Between the antapical horns the pericyst is concave. The surface of the pericyst in unornamented. The endocyst is generally appressed against the pericyst except in each of the antapical horns where the separation is clearly indicated. In the poorly developed apical horn, the separation of endo- and pericyst is not always marked. The archeopyle, generally not developed, is intercalary and relatively large.
Dimensions of the endocyst: Holotype: 40 µm long and 32 µm wide. Other specimens: between 30 and 40 µm long and 27 and 38 µm wide.
Length of the antapical horns: Holotype: 11 and 9 µm. Other specimens: generally between 5 and 12.5 µm. Length of the apical horn: Holotype: 3 µm. Other specimens: generally between 2 and 3 µm. Dimensions of the pericyst: Holotype: 55 µm long and 34 µm wide. Other specimens: between 40 and 55 µm long and 30 to 42 µm wide.
Holotype: De Coninck, 1986, pl.8, fig.1-3
Locus typicus: Woensdrecht borehole, S Netherlands
Stratum typicum: Rupelian
Original diagnosis: De Coninck, 1986, p.18
The pericyst is dorsoventrally flattened. Its ambitus is peridinoid. The epicyst is generally a little longer than the hypocyst and has a more or less triangular outline. The apical horn is poorly developed and rounded. The cingular margins are marked on the ambitus by short protrusions between which the cingulum is represented by a shallow depression. Generally the cingulum and sulcus are invisible on the dorsal and ventral surfaces of the pericyst. The hypocyst is trapezium-shaped with two protruding antapical horns with a pointed, often flexuous tip. One of the antapical horns is a little longer than the other. Between the antapical horns the pericyst is concave. The surface of the pericyst in unornamented. The endocyst is generally appressed against the pericyst except in each of the antapical horns where the separation is clearly indicated. In the poorly developed apical horn, the separation of endo- and pericyst is not always marked. The archeopyle, generally not developed, is intercalary and relatively large.
Dimensions of the endocyst: Holotype: 40 µm long and 32 µm wide. Other specimens: between 30 and 40 µm long and 27 and 38 µm wide.
Length of the antapical horns: Holotype: 11 and 9 µm. Other specimens: generally between 5 and 12.5 µm. Length of the apical horn: Holotype: 3 µm. Other specimens: generally between 2 and 3 µm. Dimensions of the pericyst: Holotype: 55 µm long and 34 µm wide. Other specimens: between 40 and 55 µm long and 30 to 42 µm wide.