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Rhynchodiniopsis hadra
Rhynchodiniopsis hadra (Sarjeant, 1966) Sarjeant, 1982
Now Leptodinium?. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly (and now) Leptodinium?.
Holotype: Sarjeant, 1966, pl.14, fig.1
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Barremian
Original diagnosis: Sarjeant, 1966, p. 119: Gonyaulacysta hadra
A Gonyaulacysta with thick-walled, spherical to spheroidal shell and long, tapering apical horn. Tabulation 4", ?oa, 6"", 6c, 6""", 1p, 1p.v., 1""""; poorly marked by crests in form of very low ridges bearing well spaced, extremely abbreviate spinelets. Cingulum weakly spiral: sulcus short, confined to ventral region. Surface generally densely granular. Dimensions: holotype: overall length 151 µm, breadth 117 µm. Shell length 117 µm; length of horn 34 µm; breadth of cingulum c.7 µm. Paratype: overall length 145 µm, breadth c.112 µm; shell length 105 µm; length of horn 40 µm; breadth of cingulum c.5 µm- Range: overall length c.140-155 µm.
Original description: Sarjeant, 1966, p. 120-121: Gonyaulacysta hadra
This is an unusually large and very characteristic species, quite frequent at this horizon, some 20 specimens having been studied. The dense granulation and relatively inconspicuous character of the crests render the tabulation difficult to determine: Text-fig. 28 was prepared from study of several specimens and is unlikely to be accurate in detail. On most specimens, including the holotype, granules are absent from various small patches of the surface: this appears to result from damage. Granulation is consistently faint or lacking on the sulcus, which is somewhat sunken. The test is spherical to spheroidal and composed of two distinct layers; a fairly thin periphragm and a thicker endophragm. The endophragm bulges only into the base of the apical horn, so that the horn contains a cavity between the wall layers. Four apical plates are present, jointly forming the apical horn. Plate I" is long and broad, occupying the anterior prolongation of the sulcus. An anterior inter-
calary plate could not be determined. Six precingular plates are present, plates 1"" and 6"" being reduced. There are also six postcingular plates, with plate 1""" reduced to accommodate the large posterior intercalary plate. A narrow posterior ventral plate separates the polygonal antapical plate from the sulcus.
The cingulum forms a feebly laevorotatory spiral, its two ends scarcely differing in antero-posterior position. The sulcus is short, extending only over the middle third of the ventral surface: it is widest at mid-point and tapers to anterior and posterior. A precingular archaeopyle, formed by loss of plate 3", is present in all specimens seen.
Now Leptodinium?. Originally Gonyaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly (and now) Leptodinium?.
Holotype: Sarjeant, 1966, pl.14, fig.1
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Barremian
Original diagnosis: Sarjeant, 1966, p. 119: Gonyaulacysta hadra
A Gonyaulacysta with thick-walled, spherical to spheroidal shell and long, tapering apical horn. Tabulation 4", ?oa, 6"", 6c, 6""", 1p, 1p.v., 1""""; poorly marked by crests in form of very low ridges bearing well spaced, extremely abbreviate spinelets. Cingulum weakly spiral: sulcus short, confined to ventral region. Surface generally densely granular. Dimensions: holotype: overall length 151 µm, breadth 117 µm. Shell length 117 µm; length of horn 34 µm; breadth of cingulum c.7 µm. Paratype: overall length 145 µm, breadth c.112 µm; shell length 105 µm; length of horn 40 µm; breadth of cingulum c.5 µm- Range: overall length c.140-155 µm.
Original description: Sarjeant, 1966, p. 120-121: Gonyaulacysta hadra
This is an unusually large and very characteristic species, quite frequent at this horizon, some 20 specimens having been studied. The dense granulation and relatively inconspicuous character of the crests render the tabulation difficult to determine: Text-fig. 28 was prepared from study of several specimens and is unlikely to be accurate in detail. On most specimens, including the holotype, granules are absent from various small patches of the surface: this appears to result from damage. Granulation is consistently faint or lacking on the sulcus, which is somewhat sunken. The test is spherical to spheroidal and composed of two distinct layers; a fairly thin periphragm and a thicker endophragm. The endophragm bulges only into the base of the apical horn, so that the horn contains a cavity between the wall layers. Four apical plates are present, jointly forming the apical horn. Plate I" is long and broad, occupying the anterior prolongation of the sulcus. An anterior inter-
calary plate could not be determined. Six precingular plates are present, plates 1"" and 6"" being reduced. There are also six postcingular plates, with plate 1""" reduced to accommodate the large posterior intercalary plate. A narrow posterior ventral plate separates the polygonal antapical plate from the sulcus.
The cingulum forms a feebly laevorotatory spiral, its two ends scarcely differing in antero-posterior position. The sulcus is short, extending only over the middle third of the ventral surface: it is widest at mid-point and tapers to anterior and posterior. A precingular archaeopyle, formed by loss of plate 3", is present in all specimens seen.