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Evansia perireticulata
Evansia perireticulata (Arhus et al., 1989) Lentin and Williams, 1993
Originally Crussolia, subsequently (and now) Evansia.
Holotype: Arhus et al., 1989, fig.5a
Locus typicus: Barents Sea
Stratum typicum: Callovian
Original description: Arhus et al., 1989, p.46: Crussolia perireticulata
Crussolia perireticulata n. sp.Fig. Sa-i
Holotype: Core 4B, 3.88 m slide 2, England Finder reference X16/4, fig. Sa; Callovian.
Paratypes: Approximately 50 specimens from cores 4B, 3 and 3B offshore Helgeland, Norway and 10 specimens from Kong Karls Land, Svalbard.
Occurrence: This species occurs commonly in the oldest of the three Callovian cores described here (core 4B). Scattered specimens are also found in the younger Callovian cores (3 and 3B). The species has been recorded from the Late Bathonian to Early Oxfordian succession at Hårfagrehaugen on Kongsøya, Kong Karls Land (Smelror, pers. observation 1987).
Description: Proximate cyst, ambitus ovoidal tapering to an apical horn, antapex rounded. Overall dimensions (70--96 x 41--63 µm (Helgeland) and 96-107 x 57--68 µm (Kong Karls Land). Cyst wall two-layered, holocavate. Pericoel best developed apically and antapically; the distance between the walls antapically may be around 6 µm when the pericoel is well preserved. Apically the endophragm forms a short blunt horn which protrudes into the Ionger horn of the periphragm. The Iength of the horn (the distance between the walls apically) varies from 4 to 11 !J.m and the blunt horn often ends in a thickened apicular structure. Finely reticulate ridges connect thick endophragm and thin periphragm. These ridges are also connected on the periphragm and form an irregular meshwork of wall thickenings which apparently do not refiect the paratabulation. This reticulum is variably developed and may be noncontinuous.
In a few well-preserved specimens the paracingulum and/or parasulcus may be seen as non-reticulate areas. A well-developed sulcus has only been observed on a single specimen and appears as a structure which continues far down
on the hypocyst. Archeopyle intercalary, 3I, opercular pieces often occur in place, but may be lost individually. The archeopyle formation weakens the cysts so much that they may break along the apical margin of the precingular paraplates on the ventral side.
Remarks: All the recorded cavate specimens with 3I archeopyles from Helgeland betong in this genus. In the material from Kong Karls Land there also occur a few specimens of the nonreticulate and tabulated C. dalei described by
Smelror & Århus (in press). Wolfard & van Erve (1981) erected the genus Crussolia for circumcavate Pareodiniaceae with 3I or SI archeopyles. All the specimens in our material in which archeopyle interpretation has been possible revealed 3I archeopyles. One specimen, which Wolfard & van Erve (1981) figured and use as their main evidence for a SI interpretation, has only three paraplates inside the cyst. During examination of additional material of C. deflandrei from the type section of Mt. Crussol, we observed only specimens with 3I archeopyles.
Supplemental description: Bailey and Partington, 1991, p.245: Crussolia perireticulata
Proximate pareodinioid dinocyst with a pyriform outline and of intermediate to large size (60-100 Ám). Cysts circumcavate with thicker, scabrate endophragm and thinner, smoother periphragm. The periphragm is modified into an imperfect reticulum that may be perforate or vacuolate. There are generally no indications of tabulation other than the archaeopyle. Some specimens have a larger, more regular reticulate ornament along the cingulum.
Originally Crussolia, subsequently (and now) Evansia.
Holotype: Arhus et al., 1989, fig.5a
Locus typicus: Barents Sea
Stratum typicum: Callovian
Original description: Arhus et al., 1989, p.46: Crussolia perireticulata
Crussolia perireticulata n. sp.Fig. Sa-i
Holotype: Core 4B, 3.88 m slide 2, England Finder reference X16/4, fig. Sa; Callovian.
Paratypes: Approximately 50 specimens from cores 4B, 3 and 3B offshore Helgeland, Norway and 10 specimens from Kong Karls Land, Svalbard.
Occurrence: This species occurs commonly in the oldest of the three Callovian cores described here (core 4B). Scattered specimens are also found in the younger Callovian cores (3 and 3B). The species has been recorded from the Late Bathonian to Early Oxfordian succession at Hårfagrehaugen on Kongsøya, Kong Karls Land (Smelror, pers. observation 1987).
Description: Proximate cyst, ambitus ovoidal tapering to an apical horn, antapex rounded. Overall dimensions (70--96 x 41--63 µm (Helgeland) and 96-107 x 57--68 µm (Kong Karls Land). Cyst wall two-layered, holocavate. Pericoel best developed apically and antapically; the distance between the walls antapically may be around 6 µm when the pericoel is well preserved. Apically the endophragm forms a short blunt horn which protrudes into the Ionger horn of the periphragm. The Iength of the horn (the distance between the walls apically) varies from 4 to 11 !J.m and the blunt horn often ends in a thickened apicular structure. Finely reticulate ridges connect thick endophragm and thin periphragm. These ridges are also connected on the periphragm and form an irregular meshwork of wall thickenings which apparently do not refiect the paratabulation. This reticulum is variably developed and may be noncontinuous.
In a few well-preserved specimens the paracingulum and/or parasulcus may be seen as non-reticulate areas. A well-developed sulcus has only been observed on a single specimen and appears as a structure which continues far down
on the hypocyst. Archeopyle intercalary, 3I, opercular pieces often occur in place, but may be lost individually. The archeopyle formation weakens the cysts so much that they may break along the apical margin of the precingular paraplates on the ventral side.
Remarks: All the recorded cavate specimens with 3I archeopyles from Helgeland betong in this genus. In the material from Kong Karls Land there also occur a few specimens of the nonreticulate and tabulated C. dalei described by
Smelror & Århus (in press). Wolfard & van Erve (1981) erected the genus Crussolia for circumcavate Pareodiniaceae with 3I or SI archeopyles. All the specimens in our material in which archeopyle interpretation has been possible revealed 3I archeopyles. One specimen, which Wolfard & van Erve (1981) figured and use as their main evidence for a SI interpretation, has only three paraplates inside the cyst. During examination of additional material of C. deflandrei from the type section of Mt. Crussol, we observed only specimens with 3I archeopyles.
Supplemental description: Bailey and Partington, 1991, p.245: Crussolia perireticulata
Proximate pareodinioid dinocyst with a pyriform outline and of intermediate to large size (60-100 Ám). Cysts circumcavate with thicker, scabrate endophragm and thinner, smoother periphragm. The periphragm is modified into an imperfect reticulum that may be perforate or vacuolate. There are generally no indications of tabulation other than the archaeopyle. Some specimens have a larger, more regular reticulate ornament along the cingulum.