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Sirmiodiniopsis orbis
Sirmiodiniopsis orbis Drugg, 1978
Tax. sr. synonym of Sirmiodiniopsis triaperta (Beju, 1979) I,entin and Williams, 1981, according to Riley and Fenton, 1982.
Holotype: Drugg, 1978, pl.7, fig.11
Isotypes: Drugg, 1978, pl.8, fig.1-3
Locus typicus: Hacknes Rock, Yorkshire, England
Stratum typicum: Callovian
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999
Sirmiodiniopsis orbis Drugg, 1978. Two fairly large and more or less elliptical openings occur on the periphragm, one on each side of the antapex. These holes are usually skewed to the ventral side. Size: overall 45 to 65 µm, generally 50 µm. Paracingulum 3-4 µm wide
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Original description: Drugg, 1978, p.73
Cyst dorsoventrally flattened, subcircular in outline. The endophragm and periphragm are in contact on the ventral and dorsal sides but pericoels are developed laterally and antapically. The endocyst is more or less circular in outline. The endophragm is about 1 µm thick and the surface is shagreen to finely granulate. The periphragm is 1 µm or a litte less in thickness and is usually quite smooth although sometimes it may be somewhat granulate. A paracingulum is present on the periphragm and is delineated by very low narrow ledges. The paracingulum is 3-4 µm wide and is slightly concave. It is circular to slightly laevorotaory. A parasulcus is usually faintly expressed on the hypocyst. The archaeopyle is apical and the operculum is removed as a single unit. The outline of separated opercula, which probably belong to this species, suggests that the operculum is compound and consists of 4 apical paraplates. The rim of the archaeopyle is angular and breaks often extend downward on the epicyst. The number of angles and straight areas along the achaeopyle edge suggest the presence of 6 precingular paraplates. A parasulcal notch is usually quite prminent. Distinct signs of paratabulation on the hypocyst are lacking. Two fairly large and more or less elliptical openings are present in the periphragm, one on each side of the antapex.These holes are usually skewed to the ventral side of the cyst The overall cyst diameter is about 45-65 µm with most specimens measuring about 50 µm. The maximum expansion of the pericoel is about 10 µm. Measurements based on 18 specimens.
Affinities:
Drugg 1978, p. 73
Sirmiodiniopsis orbis is similar to Scriniodinium pseudocrystallinum Beju 1971, which should be referred to Sirmiodinium, and is no doubt a jr. synonym of S. grossii Alberti 1961, in view of the range of variation documented by Warren 1973. Sirmiodiniopsis orbis differs from Sirmiodinium grossii by possessing two antapical openings rather than one. In addition the operculum of S. orbis does not tend to remain attached to the epicyst as it does in S. grossii. Gen. et sp. indet. of Gocht 1970 (pl.33, fig.14-15) bears a close resemblance to S. orbis, although the specimen in pl.23, fig.24 appears to have one antapical opening.
Tax. sr. synonym of Sirmiodiniopsis triaperta (Beju, 1979) I,entin and Williams, 1981, according to Riley and Fenton, 1982.
Holotype: Drugg, 1978, pl.7, fig.11
Isotypes: Drugg, 1978, pl.8, fig.1-3
Locus typicus: Hacknes Rock, Yorkshire, England
Stratum typicum: Callovian
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999
Sirmiodiniopsis orbis Drugg, 1978. Two fairly large and more or less elliptical openings occur on the periphragm, one on each side of the antapex. These holes are usually skewed to the ventral side. Size: overall 45 to 65 µm, generally 50 µm. Paracingulum 3-4 µm wide
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Original description: Drugg, 1978, p.73
Cyst dorsoventrally flattened, subcircular in outline. The endophragm and periphragm are in contact on the ventral and dorsal sides but pericoels are developed laterally and antapically. The endocyst is more or less circular in outline. The endophragm is about 1 µm thick and the surface is shagreen to finely granulate. The periphragm is 1 µm or a litte less in thickness and is usually quite smooth although sometimes it may be somewhat granulate. A paracingulum is present on the periphragm and is delineated by very low narrow ledges. The paracingulum is 3-4 µm wide and is slightly concave. It is circular to slightly laevorotaory. A parasulcus is usually faintly expressed on the hypocyst. The archaeopyle is apical and the operculum is removed as a single unit. The outline of separated opercula, which probably belong to this species, suggests that the operculum is compound and consists of 4 apical paraplates. The rim of the archaeopyle is angular and breaks often extend downward on the epicyst. The number of angles and straight areas along the achaeopyle edge suggest the presence of 6 precingular paraplates. A parasulcal notch is usually quite prminent. Distinct signs of paratabulation on the hypocyst are lacking. Two fairly large and more or less elliptical openings are present in the periphragm, one on each side of the antapex.These holes are usually skewed to the ventral side of the cyst The overall cyst diameter is about 45-65 µm with most specimens measuring about 50 µm. The maximum expansion of the pericoel is about 10 µm. Measurements based on 18 specimens.
Affinities:
Drugg 1978, p. 73
Sirmiodiniopsis orbis is similar to Scriniodinium pseudocrystallinum Beju 1971, which should be referred to Sirmiodinium, and is no doubt a jr. synonym of S. grossii Alberti 1961, in view of the range of variation documented by Warren 1973. Sirmiodiniopsis orbis differs from Sirmiodinium grossii by possessing two antapical openings rather than one. In addition the operculum of S. orbis does not tend to remain attached to the epicyst as it does in S. grossii. Gen. et sp. indet. of Gocht 1970 (pl.33, fig.14-15) bears a close resemblance to S. orbis, although the specimen in pl.23, fig.24 appears to have one antapical opening.