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Millioudodinium boreas
Millioudodinium? boreas (Davey, 1974) Stover and Evitt, 1978
Now Cribroperidinium. Originally Gonyaulacysta, subsequently Millioudodinium?, thirdly (and now) Cribroperidinium.
Stover and Evitt, 1978, considered this to be a provisionallv accepted species of Millioudodinium.
Holotype: Davey, 1974, pl.4, figs.1-4; Jan du Chêne et al., 1986, pl.21, figs.1-4
Locus typicus: Speeton, England
Stratum typicum: Late Barremian
Original diagnosis: Davey, 1974, p.52: Gonyaulacysta boreas
The cyst is ovoidal with a broad apical horn which merges imperceptibly into the main portion of the body. The cyst wall is of moderate thickness, lightly pitted to fibrous and bears a few intratabular, lightly striate elongate tubercles. The sutural crests are very well developed; they are relatively high, thin and markedly fenestrate. The fenestrations are large, generally of an ovoidal shape and extend from the cyst wall to the outer perimeter which is smooth. A fibrous apical tuft may be present. The cingulum divides the cyst into approximately equal halves; the displacement of the cingulum along the sulcus is equal to the cingulum width. The reflected tabulation is 4", 6", ?6c, 6""", 1p, 1"""". A precingular archaeopyle is formed by the detachment of plate 3".
DimensionsHolotypeRange
Central body length74 Ám59(69)76 Ám
Central body width50 Ám55(58)64 Ám
Height of apical horn6 Ám12-16 Ám
Maximum height of crests2Ám5-6 Ám
Original description: Davey, 1974, p.53: Gonyaulacysta boreas
The cyst wall is 1.5 to 2 Ám thick. The intratabular spines are short (2-3 Ám), broad based with longitudinally running fibres which extend onto the cyst surface. The apical tuft, which is usually broken, consists initially of a weak fibrous extension of the periphragm at the cyst apex; it then thickens medially before terminating with a fine network. The crests are very distinctive and particularly noticeable around the cyst circumference. The perforations are so large that often the crests appear to consist of small membranous processes which are linked distally by trabeculae. The perforations always have a smooth outline. The sulcus is narrow on the epitract and broadens antapically on the hypotract. Plates 1""" and 1p appear to be an integral part of it and are in series with a large posterior ventral plate which extends up the left side of the sulcus. These three plates surround a deep groove within the sulcus on the hypotract. The postcingular plates 3, 4 and 5 are distinctively large. The antapical plate lies entirely on the ventral surface, antapically to the sulcus, and the dorsal hypotract is composed only of plates 4""" and 5""". Thus the crest separating plate 1"""" from 4""" and 5""" occupies the antapex and is very noticeable.
Affinities:
Davey, 1974, p.53: Gonyaulacysta boreas
G. boreas may be distinguished by its overall shape, tabulation and type of sutural crests. Similar crests seem to be partly present in Gonyaulacysta scotti (Cookson and Eisenack 1958), from the Upper Jurassic of Australia, but these are much less well developed and the apical region is different. The wall structure of G. boreas is similar to that of G. tenuiceras (Eisenack, 1958) but other similarities are absent.
Now Cribroperidinium. Originally Gonyaulacysta, subsequently Millioudodinium?, thirdly (and now) Cribroperidinium.
Stover and Evitt, 1978, considered this to be a provisionallv accepted species of Millioudodinium.
Holotype: Davey, 1974, pl.4, figs.1-4; Jan du Chêne et al., 1986, pl.21, figs.1-4
Locus typicus: Speeton, England
Stratum typicum: Late Barremian
Original diagnosis: Davey, 1974, p.52: Gonyaulacysta boreas
The cyst is ovoidal with a broad apical horn which merges imperceptibly into the main portion of the body. The cyst wall is of moderate thickness, lightly pitted to fibrous and bears a few intratabular, lightly striate elongate tubercles. The sutural crests are very well developed; they are relatively high, thin and markedly fenestrate. The fenestrations are large, generally of an ovoidal shape and extend from the cyst wall to the outer perimeter which is smooth. A fibrous apical tuft may be present. The cingulum divides the cyst into approximately equal halves; the displacement of the cingulum along the sulcus is equal to the cingulum width. The reflected tabulation is 4", 6", ?6c, 6""", 1p, 1"""". A precingular archaeopyle is formed by the detachment of plate 3".
DimensionsHolotypeRange
Central body length74 Ám59(69)76 Ám
Central body width50 Ám55(58)64 Ám
Height of apical horn6 Ám12-16 Ám
Maximum height of crests2Ám5-6 Ám
Original description: Davey, 1974, p.53: Gonyaulacysta boreas
The cyst wall is 1.5 to 2 Ám thick. The intratabular spines are short (2-3 Ám), broad based with longitudinally running fibres which extend onto the cyst surface. The apical tuft, which is usually broken, consists initially of a weak fibrous extension of the periphragm at the cyst apex; it then thickens medially before terminating with a fine network. The crests are very distinctive and particularly noticeable around the cyst circumference. The perforations are so large that often the crests appear to consist of small membranous processes which are linked distally by trabeculae. The perforations always have a smooth outline. The sulcus is narrow on the epitract and broadens antapically on the hypotract. Plates 1""" and 1p appear to be an integral part of it and are in series with a large posterior ventral plate which extends up the left side of the sulcus. These three plates surround a deep groove within the sulcus on the hypotract. The postcingular plates 3, 4 and 5 are distinctively large. The antapical plate lies entirely on the ventral surface, antapically to the sulcus, and the dorsal hypotract is composed only of plates 4""" and 5""". Thus the crest separating plate 1"""" from 4""" and 5""" occupies the antapex and is very noticeable.
Affinities:
Davey, 1974, p.53: Gonyaulacysta boreas
G. boreas may be distinguished by its overall shape, tabulation and type of sutural crests. Similar crests seem to be partly present in Gonyaulacysta scotti (Cookson and Eisenack 1958), from the Upper Jurassic of Australia, but these are much less well developed and the apical region is different. The wall structure of G. boreas is similar to that of G. tenuiceras (Eisenack, 1958) but other similarities are absent.