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Meiourogonyaulax sagena
Meiourogonyaulax sagena (Duxbury, 1980, p.127, pl.3, figs.6,9,12–13) Lentin and Williams, 1981, p.182. Emendation: Harding, 1990b, p.35, as Meiourogonyaulax sagena.
Now Ellipsoidictyum. Originally Lithodinia, subsequently Meiourogonyaulax, thirdly (and now) Ellipsoidictyum.
This species was retained in Ellipsoidictyum Klement, 1960, by Williams et al., 1993, who incorrectly cited it as a new combination.
Holotype: Duxbury, 1980, pl. 3, fig. 6,9,12
Paratypes: Duxbury, 1980, pl. 3, fig. 13
Locus typicus: Speeton, Yorkshire, England
Stratum typicum: Barremian
Original description: Duxbury, 1980, p. 127: Lithodinia sagena
Diagnosis: A thin-walled species of Lithodinia which has a spheroidal endocyst bearing a low surface reticulum. The reticulum may be fine or coarse, entire or degenerate. A delicate pericyst completely envelopes the thicker endocyst and the body layers are attached along the distal margin of the reticulum. The pericyst has regularly denticulate crests which mark out a typically gonyaulacacean paratabulation pattern. The archeopyle is apical, tetratabular and the operculum sometimes attached in the parasulcal region.
Dimensions: Holotype 44x52 Ám. Overall 55(48)44x61(49)44 Ám, 16 specimens measured.
Emended diagnosis: Harding, 1990, p. 35
Shape: Ambitus subcircular to subhexagonal. Both apex and antapex flattened. Greatest width across paracingulum. An apical prominence is sometimes developed. Epicyst and hypocyst of equal length. Moderate dorso-ventral compression.
Phragma: Autophragm up to 4 Ám thick. Microgranular surface (granulae partly fused) has rugulate sculptural elements forming a low nontabular reticulum. The rugulae may be prominent (up to 2 Ám high and 5 Ám wide) or virtually undeveloped. The rugulate reticulum supports a very delicate ectophragm ( ca. 0.1 Ám thick) which is prone to removal during the oxidation process. The parasutures are delineated by single rows of pointed and occasionally ribbed denticles ( 1 Ám wide by 3 Ám long) - although exceptionally these may be absent.
Paratabulation: L-type sexiform gonyaulacoid. Paratabulation formula interpreted from the parasutural denticles: pr, 4", 6", 6c, 6""", 1"""", 1p, 5s.
Archaeopyle: Type (tA). Operculum free, simple polyplacoid. Archaeopyle suture deeply indented on the ventral surface forming a U-shaped notch as A and lu are almost equal in length.
Paracingulum: Well developed, weakly laevorotatory, displaced by 1/2-1 cingulum width.
Parasulcus: Narrow on epicyst but a broad conspicuous on the hypocyst - up to 10 Ám wide. Ii/lm suppressed. Z characteristically displaced to the right.
Dimensions: Length, + operculum (60) 48.3 (41) Ám. Width (60) 47.9 (41) Ám. Specimens = 46 (18).
Affinities:
Duxbury, 1980, p. 127: Lithodinia sagena
This species most closely resembles Cassiculosphaeridia reticulata Davey, 1969 in size shape and in possessing a low reticulum. The presence of denticulate parasutural crests marking out a gonyaulacacean paratabulation, however, dictates its inclusion in Lithodinia. Both the endocyst reticulum and the parasutural crests are quite variable. The reticulum may be fine, regular and entire but equally may be coarse, irregular and degenerate. The parasutural crests may vary in height and the denticles may be slender, long and closely spaced or may be broad-based, short and widely separated. The parasutural crestal patterns appears to bear no relationship to the underlying endocyst reticulum.
Consequently, long, straight parasutural crests, particularly on the dorsal surface and bordering the paraicingulum, are often seen to cut directly across the reticular ramifications beneath.
Remarks:
Harding, 1990, p. 35: Study of new topotype material (and additional material from the other localities studied) of this species has clarified some of the more poorly known morphological features. Duxbury (1980: 127) interpretation of an endocyst and a pericyst in this species is incorrect as the outer wall layer is supported on the nontabular rugulate reticulum. This makes the wall layers involved the autophragm and ectophragm (sensu Evitt 1985) resulting in a very similar morphology to Cassiculosphaeridia as interpreted in this work. Paratabulation pattern for the apical area has not been determined, but Y is symmetrical and the ventral area possesses a lu/li arrangement (Helenes 1986).
Now Ellipsoidictyum. Originally Lithodinia, subsequently Meiourogonyaulax, thirdly (and now) Ellipsoidictyum.
This species was retained in Ellipsoidictyum Klement, 1960, by Williams et al., 1993, who incorrectly cited it as a new combination.
Holotype: Duxbury, 1980, pl. 3, fig. 6,9,12
Paratypes: Duxbury, 1980, pl. 3, fig. 13
Locus typicus: Speeton, Yorkshire, England
Stratum typicum: Barremian
Original description: Duxbury, 1980, p. 127: Lithodinia sagena
Diagnosis: A thin-walled species of Lithodinia which has a spheroidal endocyst bearing a low surface reticulum. The reticulum may be fine or coarse, entire or degenerate. A delicate pericyst completely envelopes the thicker endocyst and the body layers are attached along the distal margin of the reticulum. The pericyst has regularly denticulate crests which mark out a typically gonyaulacacean paratabulation pattern. The archeopyle is apical, tetratabular and the operculum sometimes attached in the parasulcal region.
Dimensions: Holotype 44x52 Ám. Overall 55(48)44x61(49)44 Ám, 16 specimens measured.
Emended diagnosis: Harding, 1990, p. 35
Shape: Ambitus subcircular to subhexagonal. Both apex and antapex flattened. Greatest width across paracingulum. An apical prominence is sometimes developed. Epicyst and hypocyst of equal length. Moderate dorso-ventral compression.
Phragma: Autophragm up to 4 Ám thick. Microgranular surface (granulae partly fused) has rugulate sculptural elements forming a low nontabular reticulum. The rugulae may be prominent (up to 2 Ám high and 5 Ám wide) or virtually undeveloped. The rugulate reticulum supports a very delicate ectophragm ( ca. 0.1 Ám thick) which is prone to removal during the oxidation process. The parasutures are delineated by single rows of pointed and occasionally ribbed denticles ( 1 Ám wide by 3 Ám long) - although exceptionally these may be absent.
Paratabulation: L-type sexiform gonyaulacoid. Paratabulation formula interpreted from the parasutural denticles: pr, 4", 6", 6c, 6""", 1"""", 1p, 5s.
Archaeopyle: Type (tA). Operculum free, simple polyplacoid. Archaeopyle suture deeply indented on the ventral surface forming a U-shaped notch as A and lu are almost equal in length.
Paracingulum: Well developed, weakly laevorotatory, displaced by 1/2-1 cingulum width.
Parasulcus: Narrow on epicyst but a broad conspicuous on the hypocyst - up to 10 Ám wide. Ii/lm suppressed. Z characteristically displaced to the right.
Dimensions: Length, + operculum (60) 48.3 (41) Ám. Width (60) 47.9 (41) Ám. Specimens = 46 (18).
Affinities:
Duxbury, 1980, p. 127: Lithodinia sagena
This species most closely resembles Cassiculosphaeridia reticulata Davey, 1969 in size shape and in possessing a low reticulum. The presence of denticulate parasutural crests marking out a gonyaulacacean paratabulation, however, dictates its inclusion in Lithodinia. Both the endocyst reticulum and the parasutural crests are quite variable. The reticulum may be fine, regular and entire but equally may be coarse, irregular and degenerate. The parasutural crests may vary in height and the denticles may be slender, long and closely spaced or may be broad-based, short and widely separated. The parasutural crestal patterns appears to bear no relationship to the underlying endocyst reticulum.
Consequently, long, straight parasutural crests, particularly on the dorsal surface and bordering the paraicingulum, are often seen to cut directly across the reticular ramifications beneath.
Remarks:
Harding, 1990, p. 35: Study of new topotype material (and additional material from the other localities studied) of this species has clarified some of the more poorly known morphological features. Duxbury (1980: 127) interpretation of an endocyst and a pericyst in this species is incorrect as the outer wall layer is supported on the nontabular rugulate reticulum. This makes the wall layers involved the autophragm and ectophragm (sensu Evitt 1985) resulting in a very similar morphology to Cassiculosphaeridia as interpreted in this work. Paratabulation pattern for the apical area has not been determined, but Y is symmetrical and the ventral area possesses a lu/li arrangement (Helenes 1986).