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Lithodinia perforata
Lithodinia perforata Iosifova 1996
Holotype: Iosifova 1996: Plate VIII, 6a-c; Fig. 9.
Locus typicus: Tchernaya Retchka outcrop, the Ryazan district, Russia.
Stratum typicum: the Ryazanian, R. riasanensis ammonite zone, E. pharo dinocyst subzone.
Diagnosis: Iosifova 1996, p. 223, 225
Cysts small, slightly elongated. Periphragm microreticulate. Paratabulation gonyaulacoid, 4", 6", 6c, 5"", lp, 1"". Sutural ridges are low, microreticulate, with entire margins. Archeopyle apical, with zig-zag margin. Operculum not observed.
Dimensions: Length (without operculum): holotype: 35µm, range: 35-37µm; width: holotype: 30µm, range: 30-35µm. Five specimens measured.
Description: Iosifova 1996, p. 223, 225
Cysts small, slightly elongated, two-layered. Epicyst distinctly larger than the hypocyst. Paratabulation defined by low parasutural ridges (height up to 1.5 µm), with entire margins. Paratabulation formula 4", 6", 6c, 5"", lp, 1"". Paraplate 1"" small, quadrangular. Paraplate lp elongate. Suture 3""/4"" situated mid-dorsally. Paracingulum broad, slightly spiral. Parasulcus widens from apex to antapex and borders upon the antapical paraplate. Periphragm strongly perforated, so that irregular small-meshed reticulum appears. Parasutural ridges perforated, with entire margins. Archeopyle apical, with zig-zag margin. Operculum not observed.
Comparison: Several species of Lithodinia have microreticulate to foveolate periphragm: L. borealis (Sarjeant, 1980) Riley and Fenton, 1982, L. pertusa Duxbury, 1977, L. stoveri (Millioud, 1969) Gocht, 1975 and L. deflandrei (Sarjeant, 1968) Gocht, 1975. The new species differs from L. borealis by its smaller size, elongated shape and nature of the ridges. Its ridges are microperforated instead of coarsely perforated crests in L. borealis, that have the appearance of lines of spines linked by trabecula. The new species differs from L. pertusa mainly by its small size and elongated shape. In addition, it has five postcingulars and suture 3""/4"" is situated mid-dorsally. M. stoveri is much larger, has vacuolar periphragm and higher ridges. M. de~andrei has crests with short denticles, linked by trabeculae. The only two species of the genus Microdinium Cookson and Eisenack, 1960a emend. Stover and Evitt, 1978, M. cassiculum Wilson, 1984 and M. reticulatum Vozzhennikova, 1967, have a perforated periphragm. The new species differs from M. cassiculum in being much smaller and in having five postcingulars. It differs from M. reticulatum in that its ridges are perforated.
Occurrence: Tchernaya Retchka outcrop, the Ryazanian, R. riasanensis ammonite zone, E. pharo dinocyst subzone.
Holotype: Iosifova 1996: Plate VIII, 6a-c; Fig. 9.
Locus typicus: Tchernaya Retchka outcrop, the Ryazan district, Russia.
Stratum typicum: the Ryazanian, R. riasanensis ammonite zone, E. pharo dinocyst subzone.
Diagnosis: Iosifova 1996, p. 223, 225
Cysts small, slightly elongated. Periphragm microreticulate. Paratabulation gonyaulacoid, 4", 6", 6c, 5"", lp, 1"". Sutural ridges are low, microreticulate, with entire margins. Archeopyle apical, with zig-zag margin. Operculum not observed.
Dimensions: Length (without operculum): holotype: 35µm, range: 35-37µm; width: holotype: 30µm, range: 30-35µm. Five specimens measured.
Description: Iosifova 1996, p. 223, 225
Cysts small, slightly elongated, two-layered. Epicyst distinctly larger than the hypocyst. Paratabulation defined by low parasutural ridges (height up to 1.5 µm), with entire margins. Paratabulation formula 4", 6", 6c, 5"", lp, 1"". Paraplate 1"" small, quadrangular. Paraplate lp elongate. Suture 3""/4"" situated mid-dorsally. Paracingulum broad, slightly spiral. Parasulcus widens from apex to antapex and borders upon the antapical paraplate. Periphragm strongly perforated, so that irregular small-meshed reticulum appears. Parasutural ridges perforated, with entire margins. Archeopyle apical, with zig-zag margin. Operculum not observed.
Comparison: Several species of Lithodinia have microreticulate to foveolate periphragm: L. borealis (Sarjeant, 1980) Riley and Fenton, 1982, L. pertusa Duxbury, 1977, L. stoveri (Millioud, 1969) Gocht, 1975 and L. deflandrei (Sarjeant, 1968) Gocht, 1975. The new species differs from L. borealis by its smaller size, elongated shape and nature of the ridges. Its ridges are microperforated instead of coarsely perforated crests in L. borealis, that have the appearance of lines of spines linked by trabecula. The new species differs from L. pertusa mainly by its small size and elongated shape. In addition, it has five postcingulars and suture 3""/4"" is situated mid-dorsally. M. stoveri is much larger, has vacuolar periphragm and higher ridges. M. de~andrei has crests with short denticles, linked by trabeculae. The only two species of the genus Microdinium Cookson and Eisenack, 1960a emend. Stover and Evitt, 1978, M. cassiculum Wilson, 1984 and M. reticulatum Vozzhennikova, 1967, have a perforated periphragm. The new species differs from M. cassiculum in being much smaller and in having five postcingulars. It differs from M. reticulatum in that its ridges are perforated.
Occurrence: Tchernaya Retchka outcrop, the Ryazanian, R. riasanensis ammonite zone, E. pharo dinocyst subzone.