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Pterodinium alectrolophum
Pterodinium alectrolophum (Sarjeant, 1966) Below, 1982
Now Impagidinium. Originally Leptodinium, subsequently (and now) Impagidinium, thirdly Pterodinium. Lentin and Williams, 1985 retained this species in Impagidinium Stover and Evitt, 1978.
Holotype: Sarjeant, 1966, pl.15, figs.5-6; Jan du Chêne et al., 1986, pl.54, figs.15-16
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis: Sarjeant, 1966, p.134: Leptodinium alectrolophum
A Leptodinium having an ovoidal theca, without apical horn. Tabulation 4", 6", 7c, 5""", 1p, 1""""; plate boundaries bearing high, delicate crests which form slight projections at their points of junction. Sulcus and cingulum both of moderate breadth: sulcus relatively long, extending almost from apex to antapex. Cingular plate 7c roughly diamond-shaped. Apical prominence formed by junction of crests of apical plates.
Dimensions: holotype: overall length 56 µm, breadth 50 µm; shell length 47.5 µm, breadth 42.5 µm; width of cingulum c.5.5 µm. Paratype: overall length 61.5 µm, breadth 54-51 µm; shell length 50 µm, breadth 46 µm; width of cingulum c.6 µm. Other specimens observed were of intermediate dimensions.
Original description: Sarjeant, 1966, p. 135: Leptodinium alectrolophum
Theca ovoidal, an appearance of polygonality being imparted by the crests. The pericoel surface bears a coarse granulation, granules being rather regularly spaced. The crests are thin and high, with minute, inconspicuous perforations. Their distal edge is usually smooth, occasionally finely denticulate; crests of a single individual may in part have smooth, in part denticulate, edges.
The apical prominence appears to be formed solely by the junction of crests bounding the four apical plates; there appears to be no apical horn as such. Apical
plate 1" occupies the anterior extension of the sulcus; since the sulcus is long and approaches the apex, plate 1" is proportionately small. The six precingular plates
are all quite large. Presence of an anterior intercalary plate was suspected but not confirmed; if present, this plate is relatively small. Five well-developed postcingular plates are present; plate 1""" is reduced to accommodate a quadrate posterior intercalary plate. The antapex is occupied by a single, large plate.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by roughly twice its width. There are six clear cingular
plates, plus a seventh, diamond-shaped plate, here designated 7c, which lies between the posterior end of the cingulum and the sulcus. The sulcus is narrow and long, extending almost from apex to antapex.
An archaeopyle is not present in the holotype; however, the paratype has a well-developed precingular archaeopyle formed by loss of plate 3".
Affinities:
Sarjeant, 1966, p.135: Leptodinium alectrolophum
Leptodinium alectrolophum differs from all described species in its combination of crest and thecal morphology and tabulation. It resembles Gonyaulacysta gongylos in having a seventh polygonal plate at the posterior end of the cingulum, but differs in tabulation and crest form and shape. Heslertonia heslertonense has even higher crests; the surface lacks similar granulation and the tabulation is again different.
In certain orientations, the high crests of this species produce a misleading resemblance to Scriniodinium: however, detailed study shows that no pericoel is present.
Now Impagidinium. Originally Leptodinium, subsequently (and now) Impagidinium, thirdly Pterodinium. Lentin and Williams, 1985 retained this species in Impagidinium Stover and Evitt, 1978.
Holotype: Sarjeant, 1966, pl.15, figs.5-6; Jan du Chêne et al., 1986, pl.54, figs.15-16
Locus typicus: Speeton Clay, Heslerton, England
Stratum typicum: Middle Barremian
Original diagnosis: Sarjeant, 1966, p.134: Leptodinium alectrolophum
A Leptodinium having an ovoidal theca, without apical horn. Tabulation 4", 6", 7c, 5""", 1p, 1""""; plate boundaries bearing high, delicate crests which form slight projections at their points of junction. Sulcus and cingulum both of moderate breadth: sulcus relatively long, extending almost from apex to antapex. Cingular plate 7c roughly diamond-shaped. Apical prominence formed by junction of crests of apical plates.
Dimensions: holotype: overall length 56 µm, breadth 50 µm; shell length 47.5 µm, breadth 42.5 µm; width of cingulum c.5.5 µm. Paratype: overall length 61.5 µm, breadth 54-51 µm; shell length 50 µm, breadth 46 µm; width of cingulum c.6 µm. Other specimens observed were of intermediate dimensions.
Original description: Sarjeant, 1966, p. 135: Leptodinium alectrolophum
Theca ovoidal, an appearance of polygonality being imparted by the crests. The pericoel surface bears a coarse granulation, granules being rather regularly spaced. The crests are thin and high, with minute, inconspicuous perforations. Their distal edge is usually smooth, occasionally finely denticulate; crests of a single individual may in part have smooth, in part denticulate, edges.
The apical prominence appears to be formed solely by the junction of crests bounding the four apical plates; there appears to be no apical horn as such. Apical
plate 1" occupies the anterior extension of the sulcus; since the sulcus is long and approaches the apex, plate 1" is proportionately small. The six precingular plates
are all quite large. Presence of an anterior intercalary plate was suspected but not confirmed; if present, this plate is relatively small. Five well-developed postcingular plates are present; plate 1""" is reduced to accommodate a quadrate posterior intercalary plate. The antapex is occupied by a single, large plate.
The cingulum forms a strong laevorotatory spiral such that its two ends differ in antero-posterior position by roughly twice its width. There are six clear cingular
plates, plus a seventh, diamond-shaped plate, here designated 7c, which lies between the posterior end of the cingulum and the sulcus. The sulcus is narrow and long, extending almost from apex to antapex.
An archaeopyle is not present in the holotype; however, the paratype has a well-developed precingular archaeopyle formed by loss of plate 3".
Affinities:
Sarjeant, 1966, p.135: Leptodinium alectrolophum
Leptodinium alectrolophum differs from all described species in its combination of crest and thecal morphology and tabulation. It resembles Gonyaulacysta gongylos in having a seventh polygonal plate at the posterior end of the cingulum, but differs in tabulation and crest form and shape. Heslertonia heslertonense has even higher crests; the surface lacks similar granulation and the tabulation is again different.
In certain orientations, the high crests of this species produce a misleading resemblance to Scriniodinium: however, detailed study shows that no pericoel is present.