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Dinopterygium absidatum
Dinopterygium? absidatum Drugg 1978
Now Limbodinium. Originally Dinopterygium, subsequently Dinopterygium?, thirdly (and now) Limbodinium.
Riding, 1987(a), questionably included this species in Dinopterygium.
Holotype: Drugg, 1978, pl.4, fig.7; Riding, 1987(b), pl.1, fig.7
Isotype: Drugg, 1978
Locus typicus: Warboys Bridge Pit, Huntingdonshire, England
Stratum typicum: Oxfordian
Original description: Drugg, 1978, p. 66-67
In polar view the cyst is more or less circular in outline with a parasulcal depression. The paracingular flanges are absent in the region of the parasulcal re-entrant. The exact shape of the epicyst is unknown but is probably a very low cone. The hypocyst is a modified cone in shape and bears antapical extensions formed from the periphragm. The ventral side of the hypocyst is apparently quite flat in view of the fact that the cysts almost invariably assume a preferred orientation on the slide. This planar surface is sloped toward the antapex. The mode of archeopyle formation is epicystal. The paracingulum is prominent and is delineated by ledges from 8 to 13 Ám in width. The outline of the epicystal paracingular flange is somewhat angular and outer edges are slightly ragged. The hypocystal flange is more rounded in outline and the edges are denticulate in varying degrees. The periphragm of the hypocystal paracingular flange exhibits five arch-like openings which are convex outward. Often there are subsidiary elliptical openings of varying size and distribution. The endophragm is intact underneath. Both endophragm and periphragm are thin and shagreen to finely granulate. Paratabulation is present but is obscure. Low denticulate parasutural crests extend part way down the hypocyst, then disappear for aways, and then re-appear near the antapex. Those on the epicyst are only visible in the vicinity of the paracingular ledges. The paratabulation is apparently ?4", 6", xc, 6""", ?1p, 1"""". The cyst diameter, including the paracingular flanges, ranges from 73 to 112 Ám with most being about 85 Ám.
Affinities:
Drugg, 1978, p. 67: Interpretation of the species is rendered difficult by the monotonous preferred orientation. The arch-like openings in the periphragm of the hypocystal paracingular flanges are highly distinctive and make identification easy even in fragmented examples. The allocation of this species to the genus Dinopterygium seems reasonable although the morphology also suggests affinities with Ctenidodinium and Wanaea. This species appears to be a good marker for the Callovian and basal Oxfordian. The specific name is from the Latin absidatus for arched or vaulted.
Now Limbodinium. Originally Dinopterygium, subsequently Dinopterygium?, thirdly (and now) Limbodinium.
Riding, 1987(a), questionably included this species in Dinopterygium.
Holotype: Drugg, 1978, pl.4, fig.7; Riding, 1987(b), pl.1, fig.7
Isotype: Drugg, 1978
Locus typicus: Warboys Bridge Pit, Huntingdonshire, England
Stratum typicum: Oxfordian
Original description: Drugg, 1978, p. 66-67
In polar view the cyst is more or less circular in outline with a parasulcal depression. The paracingular flanges are absent in the region of the parasulcal re-entrant. The exact shape of the epicyst is unknown but is probably a very low cone. The hypocyst is a modified cone in shape and bears antapical extensions formed from the periphragm. The ventral side of the hypocyst is apparently quite flat in view of the fact that the cysts almost invariably assume a preferred orientation on the slide. This planar surface is sloped toward the antapex. The mode of archeopyle formation is epicystal. The paracingulum is prominent and is delineated by ledges from 8 to 13 Ám in width. The outline of the epicystal paracingular flange is somewhat angular and outer edges are slightly ragged. The hypocystal flange is more rounded in outline and the edges are denticulate in varying degrees. The periphragm of the hypocystal paracingular flange exhibits five arch-like openings which are convex outward. Often there are subsidiary elliptical openings of varying size and distribution. The endophragm is intact underneath. Both endophragm and periphragm are thin and shagreen to finely granulate. Paratabulation is present but is obscure. Low denticulate parasutural crests extend part way down the hypocyst, then disappear for aways, and then re-appear near the antapex. Those on the epicyst are only visible in the vicinity of the paracingular ledges. The paratabulation is apparently ?4", 6", xc, 6""", ?1p, 1"""". The cyst diameter, including the paracingular flanges, ranges from 73 to 112 Ám with most being about 85 Ám.
Affinities:
Drugg, 1978, p. 67: Interpretation of the species is rendered difficult by the monotonous preferred orientation. The arch-like openings in the periphragm of the hypocystal paracingular flanges are highly distinctive and make identification easy even in fragmented examples. The allocation of this species to the genus Dinopterygium seems reasonable although the morphology also suggests affinities with Ctenidodinium and Wanaea. This species appears to be a good marker for the Callovian and basal Oxfordian. The specific name is from the Latin absidatus for arched or vaulted.