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Gonyaulacysta gongylos
Gonyaulacysta gongylos Sarjeant, 1966
Now Rhynchodiniopsis. Originally Gonyaulacysta, subsequently Leptodinium?, thirdly (and now) Rhynchodiniopsis.
Holotype: Sarjeant 1966, pl.13, figs.1-2, text-fig.23; Jan du Chene et al., 1986, pl.93, figs.10-13
Locus typicus: Oxford Clay, Yorkshire, England
Stratum typicum: Early Oxfordian
Original diagnosis: Sarjent, 1966
A Gonyaulacysta having an almost spherical theca, with short blunt apical horn. Tabulation 4", 1a, 6", 7c, 6""", 1p, 1""""; plate boundaries usually bearing low, denticulate crests, Plate I" elongate and corresponding to anterior prolongation of sulcus; plate 4" very small, occupying horn tip. Plate 1""" reduced and elongate; its boundary with sulcus not marked by a crest. Sulcus and cingulum both relatively broad; cingular plate 7c small and pentagonal in shape.
Dimensions: holotype: overall length 47 Ám, length of horn 5 Ám; overall breadth 45 Ám; breadth of cingulum c. 5 Ám.
Original descriptoin: Sarjeant, 1966, p. 112
Theca almost spherical, but having a somewhat polygonal appearance because of the angularly set crests. The horn is tipped by plate 4"; extensions of plates 1-3" form its base. The anterior intercalary plate, Ia, is quadrate and separated from the horn by plate 3". Of the six precingular plates, plate 6" is reduced, plate 3" notably large and forming the anterior dorsal surface.
It is arguable whether there are five or six postcingular plates, since plate 1""" is
defined only by the angles formed by plates 2""" and Ip with the furrow and sulcus.
Plate 3""" is large and forms the posterior dorsal surface: plate 2" is reduced to accommodate the quadrate posterior intercalary plate. The antapex is occupied by a single polygonal plate.
The cingulum is broad and laevorotatory, its two ends differing in antero-posterior
position by the cingulum"s width. A pentagonal plate is present between the sulcus
and the more posterior end of the cingulum; this is here designated plate 7c, but
since its form does not correspond with that of the other cingular plates, a special
name might be merited. The sulcus is narrow in its anterior portion, broadening to
contact with the cingulum and thenceforward remaining of constant breadth in its
posterior portion.
The surface of the periphragm is generally smooth, but bears a sparse scatter of
coarse granules. The crests are strong but low, with well marked denticulations,
resembling in form crest type f. of Gonyaulacysta jurassica.
Affinities:
Sarjeant, 1966, p. 112: Gonyaulacysta gongylos is an unusually small species characterised by its overall shape, its apical tabulation, and the presence of plate 7g (sic - should be 7c; LPP). Reexamination of the holotype under a more powerful microscope has led to a fuller elucidation of the structure, in particular with regard to the crest form and the pattern of postcingular plates (a presumed plate boundary being shown to be merely a fold).
Now Rhynchodiniopsis. Originally Gonyaulacysta, subsequently Leptodinium?, thirdly (and now) Rhynchodiniopsis.
Holotype: Sarjeant 1966, pl.13, figs.1-2, text-fig.23; Jan du Chene et al., 1986, pl.93, figs.10-13
Locus typicus: Oxford Clay, Yorkshire, England
Stratum typicum: Early Oxfordian
Original diagnosis: Sarjent, 1966
A Gonyaulacysta having an almost spherical theca, with short blunt apical horn. Tabulation 4", 1a, 6", 7c, 6""", 1p, 1""""; plate boundaries usually bearing low, denticulate crests, Plate I" elongate and corresponding to anterior prolongation of sulcus; plate 4" very small, occupying horn tip. Plate 1""" reduced and elongate; its boundary with sulcus not marked by a crest. Sulcus and cingulum both relatively broad; cingular plate 7c small and pentagonal in shape.
Dimensions: holotype: overall length 47 Ám, length of horn 5 Ám; overall breadth 45 Ám; breadth of cingulum c. 5 Ám.
Original descriptoin: Sarjeant, 1966, p. 112
Theca almost spherical, but having a somewhat polygonal appearance because of the angularly set crests. The horn is tipped by plate 4"; extensions of plates 1-3" form its base. The anterior intercalary plate, Ia, is quadrate and separated from the horn by plate 3". Of the six precingular plates, plate 6" is reduced, plate 3" notably large and forming the anterior dorsal surface.
It is arguable whether there are five or six postcingular plates, since plate 1""" is
defined only by the angles formed by plates 2""" and Ip with the furrow and sulcus.
Plate 3""" is large and forms the posterior dorsal surface: plate 2" is reduced to accommodate the quadrate posterior intercalary plate. The antapex is occupied by a single polygonal plate.
The cingulum is broad and laevorotatory, its two ends differing in antero-posterior
position by the cingulum"s width. A pentagonal plate is present between the sulcus
and the more posterior end of the cingulum; this is here designated plate 7c, but
since its form does not correspond with that of the other cingular plates, a special
name might be merited. The sulcus is narrow in its anterior portion, broadening to
contact with the cingulum and thenceforward remaining of constant breadth in its
posterior portion.
The surface of the periphragm is generally smooth, but bears a sparse scatter of
coarse granules. The crests are strong but low, with well marked denticulations,
resembling in form crest type f. of Gonyaulacysta jurassica.
Affinities:
Sarjeant, 1966, p. 112: Gonyaulacysta gongylos is an unusually small species characterised by its overall shape, its apical tabulation, and the presence of plate 7g (sic - should be 7c; LPP). Reexamination of the holotype under a more powerful microscope has led to a fuller elucidation of the structure, in particular with regard to the crest form and the pattern of postcingular plates (a presumed plate boundary being shown to be merely a fold).