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Pseudoceratium retusum
Pseudoceratium retusum Brideaux, 1977
Holotype: Brideaux 1977, pl.4, fig.10-12
Locus typicus: Richardson Mountains, District of Mackenzie, Canada
Stratum typicum: Barremian-Aptian
Original description: Brideaux, 1977, p. 14-15
Shape: Pericyst ambitus asymmetrical, the lefthand ambitus rounded and with a distinct apical horn and a less prominent antapical horn; the right-hand ambitus somewhat triangular and produced into a short, rounded post-cingular horn and, at the antapex, a faint right antapical bulge; pericyst length greater than width.
Endocyst closely appressed to periblast and of similar shape. Pericoel not developed; compression dorso-ventral.
Phragma: Periphragm less than 1.0 Ám thick, smooth or scabrate surface; periphragm produced to form variously shaped sculpture elements which are discrete or linked basally and/or distally, which are nonparatabular or occasionally distinctly parasutural in position, the basal linkages persistent enough to form what may be termed parasutures; intertabular sculpture commonly linked basally to form an anastomosing network, or passing into a reticulate pattern; where the reticulum is reduced in the interior of the paraplate, commonly assuming a penesutural position; individual sculpture elements are generally bifid or bifurcate, but may be spatulate, fan-shaped or acicular; distal linkage of elements at the apices of the horns in places forming a canopy-like structure; reduction of the sculpture elements may occur ventrally and dorsally on the central parts of the hypotract; sculpture element length typically 3-5 Ám but up to 8 Ám at the apices.
Paratabulation: Basal linkage of sculpture elements forming parasutural crests denoting the presence of four apical paraplates; archeopyle outline and occasional penesutural alignment of sculpture indicating presence of six precingular paraplates; paratabulation of hypocyst not determinable.
Archeopyle/operculum: Apical archeopyle formed by the loss of four apical paraplates; operculum simple, formed of the four apical paraplates, and free, but sometimes remaining partly attached or appressed to the remaining part of
the cyst. Formula A.
Pericingulum/perisulcus: Pericingulum, on some specimens, indistinctly outlined by rows of sculpture flanking a barren area, position of sulcal notch and its relation to the ventral area of reduced or absent sculpture, indicating the approximate position of the perisulcus. Variation Greatest reduction of sculpture occurs in the interior of paraplates, especially on the precingular paraplates; sculpture remains most prominent at the anterior margins, less so at the lateral margins of these paraplates; the dorsal and ventral barren regions are variably developed and may be indicated only by slight reduction in the density of the sculpture; these barren areas are scabrate to granular in the absence of major sculptural elements.
Dimensions - Length of 17 complete specimens, 93-120 Ám; length of 46 specimens
with archeopyle, 63-93 Ám width (including the postcingular horn), 68-98 Ám; apical horn length, 14-25 Ám.
Affinities:
Brideaux, 1977, p. 15: Pseudoceratium retusum differs from Pseudoceratium pelliferum Gocht in possessing broader based and rounded apical, post-cingular and antapical horns, in development of dorsal and ventral reduction of ornament and in development on most specimens of the canopy-like fusion of sculpture at the apices of the horns.
Holotype: Brideaux 1977, pl.4, fig.10-12
Locus typicus: Richardson Mountains, District of Mackenzie, Canada
Stratum typicum: Barremian-Aptian
Original description: Brideaux, 1977, p. 14-15
Shape: Pericyst ambitus asymmetrical, the lefthand ambitus rounded and with a distinct apical horn and a less prominent antapical horn; the right-hand ambitus somewhat triangular and produced into a short, rounded post-cingular horn and, at the antapex, a faint right antapical bulge; pericyst length greater than width.
Endocyst closely appressed to periblast and of similar shape. Pericoel not developed; compression dorso-ventral.
Phragma: Periphragm less than 1.0 Ám thick, smooth or scabrate surface; periphragm produced to form variously shaped sculpture elements which are discrete or linked basally and/or distally, which are nonparatabular or occasionally distinctly parasutural in position, the basal linkages persistent enough to form what may be termed parasutures; intertabular sculpture commonly linked basally to form an anastomosing network, or passing into a reticulate pattern; where the reticulum is reduced in the interior of the paraplate, commonly assuming a penesutural position; individual sculpture elements are generally bifid or bifurcate, but may be spatulate, fan-shaped or acicular; distal linkage of elements at the apices of the horns in places forming a canopy-like structure; reduction of the sculpture elements may occur ventrally and dorsally on the central parts of the hypotract; sculpture element length typically 3-5 Ám but up to 8 Ám at the apices.
Paratabulation: Basal linkage of sculpture elements forming parasutural crests denoting the presence of four apical paraplates; archeopyle outline and occasional penesutural alignment of sculpture indicating presence of six precingular paraplates; paratabulation of hypocyst not determinable.
Archeopyle/operculum: Apical archeopyle formed by the loss of four apical paraplates; operculum simple, formed of the four apical paraplates, and free, but sometimes remaining partly attached or appressed to the remaining part of
the cyst. Formula A.
Pericingulum/perisulcus: Pericingulum, on some specimens, indistinctly outlined by rows of sculpture flanking a barren area, position of sulcal notch and its relation to the ventral area of reduced or absent sculpture, indicating the approximate position of the perisulcus. Variation Greatest reduction of sculpture occurs in the interior of paraplates, especially on the precingular paraplates; sculpture remains most prominent at the anterior margins, less so at the lateral margins of these paraplates; the dorsal and ventral barren regions are variably developed and may be indicated only by slight reduction in the density of the sculpture; these barren areas are scabrate to granular in the absence of major sculptural elements.
Dimensions - Length of 17 complete specimens, 93-120 Ám; length of 46 specimens
with archeopyle, 63-93 Ám width (including the postcingular horn), 68-98 Ám; apical horn length, 14-25 Ám.
Affinities:
Brideaux, 1977, p. 15: Pseudoceratium retusum differs from Pseudoceratium pelliferum Gocht in possessing broader based and rounded apical, post-cingular and antapical horns, in development of dorsal and ventral reduction of ornament and in development on most specimens of the canopy-like fusion of sculpture at the apices of the horns.