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Pyxidinopsis fairhavenensis
Pyxidinopsis fairhavenensis De Verteuil and Norris 1996
Holotype: de Verteuil and Norris, 1996, Plate 11, figs. 9-11
Locus typicus: Herring Bay on the west shore of the Chesapeake Bay, Anne Arundel County, Maryland.
Stratum typicum: The Fairhaven Member of the Calvert Formation at the Fairhaven Section.
Original diagnosis: de Verteuil and Norris, 1996, p. 148: Pyxidiniopsis fairhavenensis
A small, ovoidal, gonyaulacoid cyst, with a coarsely granulate to incipiently rugulate wall, with or without low coni. Archeopyle simple precingular and no other evidence of tabulation.
Original description: de Verteuil and Norris, 1996, p. 148: Pyxidiniopsis fairhavenensis
Cyst small, proximate and ovoidal with a simple, slightly deltacamerate, precingular archeopyle. Archeopyle margin even, with posterior margin rectilinear and anterior margin rounded geniculate. The wall has a simple structure consisting of the homogeneous pedium 0.25 to 0.75µm thick, which extends into solid structural elements of the prismatic luxuriae up to l.5µm high (total wall thickness 0.75 to 2.0µm). Structural elements vary from simple rounded granules or tapered coni, to irregularly linear and discontinuous ridges where several granules are fused together. On specimens with the lowest prismatic luxuriae all the structural elements tend to be rounded granules ca. 0.5µm across and spaced 0.5 to 2.0µm apart, with two or three granules occasionally fused to form a short 1 to 2µm long ridge. Specimens that have thicker pedium and prismatic luxuriae tend to have better developed, though still irregular, ridges, that may deviate from linearity forming a poorly developed rugulate effect. Even on these specimens, however, low coni and tapered or rounded granules are the dominant structural elements, so truly rugulate luxuriae do not occur. In optical section the inner surface of the autoblast is even while the outer surface is irregular, with up to l.5Ám of relief. Apart from the archeopyle there are no indications of tabulation.
Dimensions: Length 28(35)41µm, holotype 30µm; width 22(29.7)35µm (based on twenty-three specimens), holotype 25µm. Breadth 26(31)35µm (based on three specimens). Twenty-six specimens measured.
Comparison: Pyxidinopsis challengerensis, Pyxidinopsis ardonensis, Pyxidinopsis bakonyensis and Pyxidinopsis densepunctata all differ from the new species in having either reticulate or punctate prismatic luxuriae. The prismatic luxuriae in Pyxidinopsis pastilliformis are well illustrated with SEM photomicrographs in the original description (Matsuoka and Head 1992, pl.3). Spherical Pyxidinopsis pastilliformis has well developed, even, microrugulate or microcerebrate, crenulated prismatic luxuriae (individual elements 0.2µm across) that are much finer than the coarse granules of Pyxidinopsis fairhavenensis. The new species is similar to Operculodinium placitum in that both taxa can have granulate prismatic luxuriae. In Operculodinium placitum however the pila of the prismatic luxuriae are uniform in size and tightly packed and the autoblast develops a second type of structural element in the form of tapered virgae. Pyxidiniopsis fairhavenensis on the other hand, lacks virgae, having instead irregular coarse granules and coni that may fuse to form discontinuous, poorly developed ridges. Pyxidiniopsis fairhavenensis differs from Operculodinim janduchenei in wall structure as well as in lacking virgae. Habibacysta tectata has a distinct wall structure comprising pedium, columellae and tegillum that is quite different from Pyxidinopsis fairhavenensis.
Remarks: Lentin and Williams (1985:302) transferred to Pyxidinopsis, without stated justification, the species Tectatodinium laminatum Davies 1983. The wall structure of Tectatodinium laminatum comprises pedium and prismatic luxuriae formed by "loosely compacted fibrils" (Davies 1983:21), that impart to the autohlast a laminar appearance in optical section. This wall structure is not at all like that of Pyxidinopsis challengerensis or any other species currently in this genus. It is however generally similar to the wall structure in Tectatodinium pellitum (see Head 1994b).
Occurrence. Lower Miocene (DN2-DN4) in the Salisbury Embayment, most commonly in the Fairhaven Member but also in the Plum Point Marls Member of the Calvert Formation.
Holotype: de Verteuil and Norris, 1996, Plate 11, figs. 9-11
Locus typicus: Herring Bay on the west shore of the Chesapeake Bay, Anne Arundel County, Maryland.
Stratum typicum: The Fairhaven Member of the Calvert Formation at the Fairhaven Section.
Original diagnosis: de Verteuil and Norris, 1996, p. 148: Pyxidiniopsis fairhavenensis
A small, ovoidal, gonyaulacoid cyst, with a coarsely granulate to incipiently rugulate wall, with or without low coni. Archeopyle simple precingular and no other evidence of tabulation.
Original description: de Verteuil and Norris, 1996, p. 148: Pyxidiniopsis fairhavenensis
Cyst small, proximate and ovoidal with a simple, slightly deltacamerate, precingular archeopyle. Archeopyle margin even, with posterior margin rectilinear and anterior margin rounded geniculate. The wall has a simple structure consisting of the homogeneous pedium 0.25 to 0.75µm thick, which extends into solid structural elements of the prismatic luxuriae up to l.5µm high (total wall thickness 0.75 to 2.0µm). Structural elements vary from simple rounded granules or tapered coni, to irregularly linear and discontinuous ridges where several granules are fused together. On specimens with the lowest prismatic luxuriae all the structural elements tend to be rounded granules ca. 0.5µm across and spaced 0.5 to 2.0µm apart, with two or three granules occasionally fused to form a short 1 to 2µm long ridge. Specimens that have thicker pedium and prismatic luxuriae tend to have better developed, though still irregular, ridges, that may deviate from linearity forming a poorly developed rugulate effect. Even on these specimens, however, low coni and tapered or rounded granules are the dominant structural elements, so truly rugulate luxuriae do not occur. In optical section the inner surface of the autoblast is even while the outer surface is irregular, with up to l.5Ám of relief. Apart from the archeopyle there are no indications of tabulation.
Dimensions: Length 28(35)41µm, holotype 30µm; width 22(29.7)35µm (based on twenty-three specimens), holotype 25µm. Breadth 26(31)35µm (based on three specimens). Twenty-six specimens measured.
Comparison: Pyxidinopsis challengerensis, Pyxidinopsis ardonensis, Pyxidinopsis bakonyensis and Pyxidinopsis densepunctata all differ from the new species in having either reticulate or punctate prismatic luxuriae. The prismatic luxuriae in Pyxidinopsis pastilliformis are well illustrated with SEM photomicrographs in the original description (Matsuoka and Head 1992, pl.3). Spherical Pyxidinopsis pastilliformis has well developed, even, microrugulate or microcerebrate, crenulated prismatic luxuriae (individual elements 0.2µm across) that are much finer than the coarse granules of Pyxidinopsis fairhavenensis. The new species is similar to Operculodinium placitum in that both taxa can have granulate prismatic luxuriae. In Operculodinium placitum however the pila of the prismatic luxuriae are uniform in size and tightly packed and the autoblast develops a second type of structural element in the form of tapered virgae. Pyxidiniopsis fairhavenensis on the other hand, lacks virgae, having instead irregular coarse granules and coni that may fuse to form discontinuous, poorly developed ridges. Pyxidiniopsis fairhavenensis differs from Operculodinim janduchenei in wall structure as well as in lacking virgae. Habibacysta tectata has a distinct wall structure comprising pedium, columellae and tegillum that is quite different from Pyxidinopsis fairhavenensis.
Remarks: Lentin and Williams (1985:302) transferred to Pyxidinopsis, without stated justification, the species Tectatodinium laminatum Davies 1983. The wall structure of Tectatodinium laminatum comprises pedium and prismatic luxuriae formed by "loosely compacted fibrils" (Davies 1983:21), that impart to the autohlast a laminar appearance in optical section. This wall structure is not at all like that of Pyxidinopsis challengerensis or any other species currently in this genus. It is however generally similar to the wall structure in Tectatodinium pellitum (see Head 1994b).
Occurrence. Lower Miocene (DN2-DN4) in the Salisbury Embayment, most commonly in the Fairhaven Member but also in the Plum Point Marls Member of the Calvert Formation.