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Endoceratium dettmanniae
Endoceratium dettmanniae (Cookson and Hughes, 1964) Stover and Evitt 1978, emend. Harding and Hughes, 1990
Originally Pseudoceratium, subsequently (and now) Endoceratium.
Morgan, 1980, also effected the transfer of this species to Endoceratium.
Helby, 1987, retained this species in Pseudoceratium Gocht, 1957.
Lentin and Williams, 1989, retained it in Endoceratium.
Holotype: Cookson and Hughes, 1964, pl.7, fig.1
Locus typicus: Cambridge Greensand, Bradfortshire, England
Stratum typicum: Late Albian-Early Cenomanian
Original diagnosis: Cookson and Hughes, 1964, p. 51: Pseudoceratium dettmanniae
Shell approximately four-sided with a longish straight-sided apical horn and a short projection at each of the three angles. Indications of a +circular girdle occur in most specimens. The shell opens by the detachment of an apical segment along a straight or slightly oblique line. The surface of the shell is scabrate except for a relatively wide finely pitted band that encircles both dorsal and ventral surfaces. Transverse sections (cut by Dr. Mary Dettmann) have shown that the shell-membrane is two-layered, the two layers being in contact and traversed by elongated pits in the region of the pitted band mentioned above and widely separated from one another in the unpitted portions of the membrane.
Emended diagnosis: Harding and Hughes, 1990, p. 312,314
Shape: Essentially rhomboidal periphragm ambitus, modified by development of apical, right postcingular and antapical horns. The horns are broad-based, usually with blunt terminations. The postcingular horn shows variable development, from a mere protrusion of the ambitus to an acuminate horn. Epicyst is usually slightly longer than the hypocyst. Greatest width is immediately post-cingular (across post-cingular horn). Strong primary dorso-ventral compression.
Phragma: Periphragm thin (1 Ám), surface finely microgranulate. The periphragm essentially consists of two halves. one dorsal, the other ventral, separated by an ambital schism. These halves are only fused in the distal regions of the horns (Fig.lJ). So, although the cyst may appear to be circumcavate in light microscopy (due to the strong dorso-ventral compression the ambital schism is difficult to identify in LM), study using the SEM reveals that these areas are not pericoels, as they open to the external environment ambitally. This feature is not an artifact (i.e. ambital splitting of the periphragm during air-drying preparation methods), as the periphragm margins are often found infolded into these cavities. The periphragm is variably perforate, especially in bands around the cyst margin (the "pitted band" of Cookson and Hughes, 1964: p.51). Plate boundaries are delineated by continuous lines of perforations.
Endophragm is about 1 Ám thick, with a laevigate surface. Endocyst ambitus is less angular than the pericyst, the horns being less prominently developed.
Paratabulation: The parasutural perforations of the periphragm reveal a corniform paratabulation as follows: 1pr, 4", 6", 6c, 7""", 1p, 1"""", Xs. Apical paratabulation is of insert arrangement, lu can also be distinguished, Iying between prominent flagellar scar and the large second postcingular (II) paraplate. Further details of the paratabulation scheme are discussed later in this study.
Archaeopyle: Type (tA), free, simple, polyplacoid operculum, sometimes remains adherent.
Cingulum: Laevorotatory, about 7 Ám wide but expanded towards right of sulcus, consisting of six plates.
Sulcus: Sulcal paratabulation is partially developed, which is rare for a ceratioid dinocyst. Anterior sulcal prominent, as is the first postcingular (lu). The latter plate clearly creates an angularity in the left margin of the sulcus, as opposed to the characteristic parallel-sided sulcal region of most ceratioids. The sulcus narrows noticeably antapically from the antapical margin of 1"""/lu. 1p/X has a distinctly camerate adcingular margin. Prominent flagellar scar, developed as a perforation in the periphragm. Paratabulation is more obscure in the region of the posterior sulcal plate.
Dimensions: Length (complete specimens including operculum)= (137)116(106) Ám. Length (specimens lacking operculum)= (112)80(67) Ám. Width= (113)88(67) Ám. Number of specimens = 16.
Originally Pseudoceratium, subsequently (and now) Endoceratium.
Morgan, 1980, also effected the transfer of this species to Endoceratium.
Helby, 1987, retained this species in Pseudoceratium Gocht, 1957.
Lentin and Williams, 1989, retained it in Endoceratium.
Holotype: Cookson and Hughes, 1964, pl.7, fig.1
Locus typicus: Cambridge Greensand, Bradfortshire, England
Stratum typicum: Late Albian-Early Cenomanian
Original diagnosis: Cookson and Hughes, 1964, p. 51: Pseudoceratium dettmanniae
Shell approximately four-sided with a longish straight-sided apical horn and a short projection at each of the three angles. Indications of a +circular girdle occur in most specimens. The shell opens by the detachment of an apical segment along a straight or slightly oblique line. The surface of the shell is scabrate except for a relatively wide finely pitted band that encircles both dorsal and ventral surfaces. Transverse sections (cut by Dr. Mary Dettmann) have shown that the shell-membrane is two-layered, the two layers being in contact and traversed by elongated pits in the region of the pitted band mentioned above and widely separated from one another in the unpitted portions of the membrane.
Emended diagnosis: Harding and Hughes, 1990, p. 312,314
Shape: Essentially rhomboidal periphragm ambitus, modified by development of apical, right postcingular and antapical horns. The horns are broad-based, usually with blunt terminations. The postcingular horn shows variable development, from a mere protrusion of the ambitus to an acuminate horn. Epicyst is usually slightly longer than the hypocyst. Greatest width is immediately post-cingular (across post-cingular horn). Strong primary dorso-ventral compression.
Phragma: Periphragm thin (1 Ám), surface finely microgranulate. The periphragm essentially consists of two halves. one dorsal, the other ventral, separated by an ambital schism. These halves are only fused in the distal regions of the horns (Fig.lJ). So, although the cyst may appear to be circumcavate in light microscopy (due to the strong dorso-ventral compression the ambital schism is difficult to identify in LM), study using the SEM reveals that these areas are not pericoels, as they open to the external environment ambitally. This feature is not an artifact (i.e. ambital splitting of the periphragm during air-drying preparation methods), as the periphragm margins are often found infolded into these cavities. The periphragm is variably perforate, especially in bands around the cyst margin (the "pitted band" of Cookson and Hughes, 1964: p.51). Plate boundaries are delineated by continuous lines of perforations.
Endophragm is about 1 Ám thick, with a laevigate surface. Endocyst ambitus is less angular than the pericyst, the horns being less prominently developed.
Paratabulation: The parasutural perforations of the periphragm reveal a corniform paratabulation as follows: 1pr, 4", 6", 6c, 7""", 1p, 1"""", Xs. Apical paratabulation is of insert arrangement, lu can also be distinguished, Iying between prominent flagellar scar and the large second postcingular (II) paraplate. Further details of the paratabulation scheme are discussed later in this study.
Archaeopyle: Type (tA), free, simple, polyplacoid operculum, sometimes remains adherent.
Cingulum: Laevorotatory, about 7 Ám wide but expanded towards right of sulcus, consisting of six plates.
Sulcus: Sulcal paratabulation is partially developed, which is rare for a ceratioid dinocyst. Anterior sulcal prominent, as is the first postcingular (lu). The latter plate clearly creates an angularity in the left margin of the sulcus, as opposed to the characteristic parallel-sided sulcal region of most ceratioids. The sulcus narrows noticeably antapically from the antapical margin of 1"""/lu. 1p/X has a distinctly camerate adcingular margin. Prominent flagellar scar, developed as a perforation in the periphragm. Paratabulation is more obscure in the region of the posterior sulcal plate.
Dimensions: Length (complete specimens including operculum)= (137)116(106) Ám. Length (specimens lacking operculum)= (112)80(67) Ám. Width= (113)88(67) Ám. Number of specimens = 16.