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Millioudodinium episomum
Millioudinium episomum (Sarjeant, 1966) Stover and Evitt, 1978
Now Leptodinium. Originally Gonvaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly (and now) Leptodinium.
Holotype: Sarjeant, 1966, pl.13, figs.9-10, text-fig.27; Jan du Chêne et al., 1986, pl.67, figs. 15-16
Locus typicus: Heslerton, England
Stratum typicum: Late Barremian
Original diagnosis: Sarjeant, 1966, p. 118: Gonyaulacysta episoma
A Gonyaulacysta with spherical to broadly ovoid shell with strong apical horn of moderate length. Tabulation 4", 1a, 6", ?5c, 6""", 1p, 1p.v., 1"""". Crests consisting of rows of thin spinelets connected distally by trabeculum; an extremely delicate membrane stretching between spinelets and trabecula. Cingulum strongly spiral; sulcus broad and short, stretching from about mid-point on epitheca to about mid-point on hypotheca. Surface densely granular; very few spines occasionally present. Horn with trifurcate appearance produced by high crest bounding plate 4".
Dimensions: holotype: overall length 80 Ám, breadth 74 Ám; shell length 70 Ám, breadth 68 Ám; horn 10 Ám in length; crests c. 2 Ám in height; cingulum c. 3 Ám broad.
Range of dimensions: overall length 80-95 Ám, horn length 10-18 Ám, breadth 60-80 Ám.
Original description: Sarjeant, 1966, p. 118-119: Gonyaulacysta episoma
An abundant species at this horizon, some 30 specimens having been examined. All show some degree of distortion as a result of compression of the originally spherical, fairly thin-walled shell. The horn is short, strongly tapering and pointed; it is tipped by plate 4", the high crest bounding this plate producing a characteristic trifurcate appearance. There are four apical plates, plate 1" occupying the anterior prolongation of the sulcus and being unusually broad. Six precingular plates are present, the sixth being reduced to accommodate the anterior intercalary plate.
Six postcingular plates are present, plate 1""" being reduced to accommodate the
posterior intercalary plate. A roughly quadrate posterior ventral plate separates
the sulcus from the single large antapical plate.
The cingulum is of moderate breadth and forms a strong laevorotatory spiral such
that its two ends differ in antero-posterior position by three times its breadth. It
comprises cetainly five, possibly six cingular plates. The sulcus is short and broad.
The surface is densely granular. In at least one specimen, a very few short spines are present on the surface of the hypotract: spines are not present, however, on the holotype. The degree of granulation of the sulcus is markedly less than that of the rest of the surface.
A precingular archaeopyle, formed by loss of plate 3"", is present in all specimens
seen.
Affinities:
Sarjeant, 1966, p. 119: Gonyaulacysta episoma
Gonyaulacysta episoma sp. nov. is characterized by its combination of shape, tabulation and crest character. Gonyaulacysta nuciformis (Deflandre 1938), from the Upper Jurassic, has a somewhat similar overall shape and degree of granulation, but the shell wall is thicker, the tabulation is less clear and the form of the crests is quite different. Gonyaulacysta scotti (Cookson & Eisenack 1958) an inadequately described species from the Upper Jurassic of Western Australia, has rather similar crests, but has a more markedly ovoidal shape and an apical horn of dissimilar type. Gonyaulacysta tenuiceras (Eisenack 1958) from the Aptian of Germany, has a horn and crests of somewhat similar character, but the crests are much higher and the tabulation is markedly different.
Now Leptodinium. Originally Gonvaulacysta, subsequently Millioudodinium, thirdly Rhynchodiniopsis, fourthly (and now) Leptodinium.
Holotype: Sarjeant, 1966, pl.13, figs.9-10, text-fig.27; Jan du Chêne et al., 1986, pl.67, figs. 15-16
Locus typicus: Heslerton, England
Stratum typicum: Late Barremian
Original diagnosis: Sarjeant, 1966, p. 118: Gonyaulacysta episoma
A Gonyaulacysta with spherical to broadly ovoid shell with strong apical horn of moderate length. Tabulation 4", 1a, 6", ?5c, 6""", 1p, 1p.v., 1"""". Crests consisting of rows of thin spinelets connected distally by trabeculum; an extremely delicate membrane stretching between spinelets and trabecula. Cingulum strongly spiral; sulcus broad and short, stretching from about mid-point on epitheca to about mid-point on hypotheca. Surface densely granular; very few spines occasionally present. Horn with trifurcate appearance produced by high crest bounding plate 4".
Dimensions: holotype: overall length 80 Ám, breadth 74 Ám; shell length 70 Ám, breadth 68 Ám; horn 10 Ám in length; crests c. 2 Ám in height; cingulum c. 3 Ám broad.
Range of dimensions: overall length 80-95 Ám, horn length 10-18 Ám, breadth 60-80 Ám.
Original description: Sarjeant, 1966, p. 118-119: Gonyaulacysta episoma
An abundant species at this horizon, some 30 specimens having been examined. All show some degree of distortion as a result of compression of the originally spherical, fairly thin-walled shell. The horn is short, strongly tapering and pointed; it is tipped by plate 4", the high crest bounding this plate producing a characteristic trifurcate appearance. There are four apical plates, plate 1" occupying the anterior prolongation of the sulcus and being unusually broad. Six precingular plates are present, the sixth being reduced to accommodate the anterior intercalary plate.
Six postcingular plates are present, plate 1""" being reduced to accommodate the
posterior intercalary plate. A roughly quadrate posterior ventral plate separates
the sulcus from the single large antapical plate.
The cingulum is of moderate breadth and forms a strong laevorotatory spiral such
that its two ends differ in antero-posterior position by three times its breadth. It
comprises cetainly five, possibly six cingular plates. The sulcus is short and broad.
The surface is densely granular. In at least one specimen, a very few short spines are present on the surface of the hypotract: spines are not present, however, on the holotype. The degree of granulation of the sulcus is markedly less than that of the rest of the surface.
A precingular archaeopyle, formed by loss of plate 3"", is present in all specimens
seen.
Affinities:
Sarjeant, 1966, p. 119: Gonyaulacysta episoma
Gonyaulacysta episoma sp. nov. is characterized by its combination of shape, tabulation and crest character. Gonyaulacysta nuciformis (Deflandre 1938), from the Upper Jurassic, has a somewhat similar overall shape and degree of granulation, but the shell wall is thicker, the tabulation is less clear and the form of the crests is quite different. Gonyaulacysta scotti (Cookson & Eisenack 1958) an inadequately described species from the Upper Jurassic of Western Australia, has rather similar crests, but has a more markedly ovoidal shape and an apical horn of dissimilar type. Gonyaulacysta tenuiceras (Eisenack 1958) from the Aptian of Germany, has a horn and crests of somewhat similar character, but the crests are much higher and the tabulation is markedly different.