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Impagidinium antecarcerem
Impagidinium antecarcerem de Verteuil and Norris, 1996
Holotype: Plate 8, figs.7-10; text-fig.34
Locus typicus: uppermost part of the Richmond City Jail Section, Richmond, Henrico County, Virginia.
Stratum typicum: Upper Miocene
Original diagnosis: de Verteuil and Norris, 1996, p. 136: Impagidinium antecarcerem
Ovoidal Impagidinium of intermediate size with low apical boss and thin, finely alveolate wall with smooth outer surface. Standard gonyaulacalean tabulation with narrow first apical field and triangular sixth precingular delimited by low limbate septa over all field boundaries outside the sulcus. Septa are lower between truncate gonal appendages and are often irregularly perforate. Sulcus is wide and straight; cingulum gently laevorotatory decending sharply distally.
Original description: de Verteuil and Norris, 1996, p. 136, 138, 140: Impagidinium antecarcerem
Cyst proximate, intermediate in size and ovoidal to subspherical with a low apical boss. The wall comprises thin pedium ca. 0.25µm thick and dense, finely alveolate luxuriae 0.5 to 0.75µm thick, with a psilate outer surface. Alveoles within the wall are ca. 0.4 to <0.2µm in diameter and closely spaced. The autoblast bears peritabular septa that attach directly to the alveolate luxuriae at the limbi. Septa are 3 to 6µm high and up to 5µm wide at their bases near gonal positions but generally less than 3,um wide intergonally. They variably decrease in height between gonal positions by between 75 and 50 % of maximum. The tegillum forming the septa is thin and psilate, ca. 0.25µm, often with small claustra that range from 0.5 to 4Ám in diameter and occur mostly over the basal pericoels. The distal ridges of septa are entire (sensu Sarjeant 1982; fig. 6) but are not invaginated (sensu Head et al. 1989b). Truncate gonal appendages extend only slightly above the septa, essentially without furcations. A single wide-based appendage is present at the apex above the apical boss; small septa and fenestra at the ventral base of this process, anterior to 1" and 4", are suggestive of an apical pore field.
The tabulation is sexiform and as for genus. The third precingular field is mid-dorsal, large and deltacamerate with weakly geniculate anterior margin. It forms the simple Type P archeopyle and occupies most of the dorsal epicyst. The sixth precinglar field is distinctly triangular with vertical side 3 and 1^2 >>90¦ due to the steeply decending sixth cingular field (pl. 8, fig. 11). 1" and 5" are large and occupy much of the ventral epicyst, extending almost to the apex. The small, stenoform first postcingular field (1"") lies partly within the sulcus; there are five larger postcingular fields that contact the antapical field. The large deltaplanate fourth postcingular field exhibits minor dextral torsion although 4""15"" is still to the right of the 3"/4" field boundary. The apex is dominated by approximately symmetrical second and third apical fields; smaller, stenoform 1" and 4" are confined to the anterior ventral surface with 1" being anterior to and smaller than 4". A 4"/1 " septum is lower than those over 3"/4" and 1"/2". Cingulum with six fields and a distal transitional field, gently laevorotatory except where distal 6c decends steeply. Cingulum width 4 to 8mm narrowing at cingular field boundaries, displaced one cingular width to 5c, two widths distally. Sulcus straight and long, ca. 12 to 15Ám wide at the cingulum and posteriorly expanded, comprising large anterior sulcul field, left and right sulcul fields, the posterior sulcul field plus a tranistional cingular field as indicated in text-figure 34. Septa variably developed or missing over sulcal field boundaries, usually present as rudimentary linear cusps.
Dimensions: Length excluding septa 45(56.4)63µm, holotype 58µm; width at cingulum excluding septa 41(47.4)55µm, holotype 51µm. Septa 2 to 7µm, usually 3 to 5µm. Twenty-six specimens measured.
Comparison: The combination of characters that together distinguish Impagidinium antecarcerem from all others in the genus are: small to intermediate size, ovoidal shape, apical boss, finely alveolate externally smooth wall, fully delimited tabulation outside the sulcus, low septa without distal invagination and with small basal fenestra and the apical series topology. Of taxa approximately this size with low septa, Impagidinium patulum and Impagidinium victorianum have some field boundaries without septa; Impagidinium californiense, Impagidinium gabrensis and Impagidinium sphaericum are spherical with septa that lack pericoels and are not intergonally depressed. Impagidinium eugublinum has granulate or pustulate luxuriae. The wall structure of Impagidinium tectum appears to be similar to Impagidinium antecarcerem in that it contains hollow spaces between pedium and tegillum; it is, however, described as columellar. Moreover, Impagidinium tectum lacks an apical boss and pericoels beneath the septa. Impagidinium antecarcerem is perhaps most similar to Impagidinium dispertitum. The latter however is significantly larger, appears to lack the alveolate wall structure characteristic of Impagidinium antecarcerem and has a well developed septum joining the lower proximal and upper distal ends of the cingulum.
Occurrence: Upper upper Miocene (DN10) in the Salisbury Embayment. Impagidinium antecarcerem has only been found to date in one sample from Richmond, Virginia. Beds of the Eastover Formation and belonging to Zone DN10 (Part I, this volume) are from inner neritic facies in their type area and contain a different assemblage from the uppermost part of the Richmond City Jail Section.
Holotype: Plate 8, figs.7-10; text-fig.34
Locus typicus: uppermost part of the Richmond City Jail Section, Richmond, Henrico County, Virginia.
Stratum typicum: Upper Miocene
Original diagnosis: de Verteuil and Norris, 1996, p. 136: Impagidinium antecarcerem
Ovoidal Impagidinium of intermediate size with low apical boss and thin, finely alveolate wall with smooth outer surface. Standard gonyaulacalean tabulation with narrow first apical field and triangular sixth precingular delimited by low limbate septa over all field boundaries outside the sulcus. Septa are lower between truncate gonal appendages and are often irregularly perforate. Sulcus is wide and straight; cingulum gently laevorotatory decending sharply distally.
Original description: de Verteuil and Norris, 1996, p. 136, 138, 140: Impagidinium antecarcerem
Cyst proximate, intermediate in size and ovoidal to subspherical with a low apical boss. The wall comprises thin pedium ca. 0.25µm thick and dense, finely alveolate luxuriae 0.5 to 0.75µm thick, with a psilate outer surface. Alveoles within the wall are ca. 0.4 to <0.2µm in diameter and closely spaced. The autoblast bears peritabular septa that attach directly to the alveolate luxuriae at the limbi. Septa are 3 to 6µm high and up to 5µm wide at their bases near gonal positions but generally less than 3,um wide intergonally. They variably decrease in height between gonal positions by between 75 and 50 % of maximum. The tegillum forming the septa is thin and psilate, ca. 0.25µm, often with small claustra that range from 0.5 to 4Ám in diameter and occur mostly over the basal pericoels. The distal ridges of septa are entire (sensu Sarjeant 1982; fig. 6) but are not invaginated (sensu Head et al. 1989b). Truncate gonal appendages extend only slightly above the septa, essentially without furcations. A single wide-based appendage is present at the apex above the apical boss; small septa and fenestra at the ventral base of this process, anterior to 1" and 4", are suggestive of an apical pore field.
The tabulation is sexiform and as for genus. The third precingular field is mid-dorsal, large and deltacamerate with weakly geniculate anterior margin. It forms the simple Type P archeopyle and occupies most of the dorsal epicyst. The sixth precinglar field is distinctly triangular with vertical side 3 and 1^2 >>90¦ due to the steeply decending sixth cingular field (pl. 8, fig. 11). 1" and 5" are large and occupy much of the ventral epicyst, extending almost to the apex. The small, stenoform first postcingular field (1"") lies partly within the sulcus; there are five larger postcingular fields that contact the antapical field. The large deltaplanate fourth postcingular field exhibits minor dextral torsion although 4""15"" is still to the right of the 3"/4" field boundary. The apex is dominated by approximately symmetrical second and third apical fields; smaller, stenoform 1" and 4" are confined to the anterior ventral surface with 1" being anterior to and smaller than 4". A 4"/1 " septum is lower than those over 3"/4" and 1"/2". Cingulum with six fields and a distal transitional field, gently laevorotatory except where distal 6c decends steeply. Cingulum width 4 to 8mm narrowing at cingular field boundaries, displaced one cingular width to 5c, two widths distally. Sulcus straight and long, ca. 12 to 15Ám wide at the cingulum and posteriorly expanded, comprising large anterior sulcul field, left and right sulcul fields, the posterior sulcul field plus a tranistional cingular field as indicated in text-figure 34. Septa variably developed or missing over sulcal field boundaries, usually present as rudimentary linear cusps.
Dimensions: Length excluding septa 45(56.4)63µm, holotype 58µm; width at cingulum excluding septa 41(47.4)55µm, holotype 51µm. Septa 2 to 7µm, usually 3 to 5µm. Twenty-six specimens measured.
Comparison: The combination of characters that together distinguish Impagidinium antecarcerem from all others in the genus are: small to intermediate size, ovoidal shape, apical boss, finely alveolate externally smooth wall, fully delimited tabulation outside the sulcus, low septa without distal invagination and with small basal fenestra and the apical series topology. Of taxa approximately this size with low septa, Impagidinium patulum and Impagidinium victorianum have some field boundaries without septa; Impagidinium californiense, Impagidinium gabrensis and Impagidinium sphaericum are spherical with septa that lack pericoels and are not intergonally depressed. Impagidinium eugublinum has granulate or pustulate luxuriae. The wall structure of Impagidinium tectum appears to be similar to Impagidinium antecarcerem in that it contains hollow spaces between pedium and tegillum; it is, however, described as columellar. Moreover, Impagidinium tectum lacks an apical boss and pericoels beneath the septa. Impagidinium antecarcerem is perhaps most similar to Impagidinium dispertitum. The latter however is significantly larger, appears to lack the alveolate wall structure characteristic of Impagidinium antecarcerem and has a well developed septum joining the lower proximal and upper distal ends of the cingulum.
Occurrence: Upper upper Miocene (DN10) in the Salisbury Embayment. Impagidinium antecarcerem has only been found to date in one sample from Richmond, Virginia. Beds of the Eastover Formation and belonging to Zone DN10 (Part I, this volume) are from inner neritic facies in their type area and contain a different assemblage from the uppermost part of the Richmond City Jail Section.