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Exochosphaeridium insigne
Exochosphaeridium insigne de Verteuil and Norris, 1996
Holotype: Plate 3, figs. 5,6, 8- 10
Locus typicus: the Popes Creek Section, Potomac River, Popes Creek, Charles County, Maryland.
Type locality: The lower Popes Creek Sand Member of the Calvert Formation.
Original diagnosis: de Verteuil and Norris, 1996, p. 116: Exochosphaeridium insigne
Cysts intermediate, proximochorate and spherical. Autoblast comprising homogeneous pedium ca. 0.5Ám thick, and dense, fibropitted luxuriae 2.0 - 4.0Ám thick with evenly distributed, nontabular, fibrous, truncate, distally truncated processes. Archeopyle simple precingular with a distinctive theta-camerate to thetafastigiate free operculum.
Original description: de Verteuil and Norris, 1996, p. 116: Exochosphaeridium insigne
The proximate luxuriae form an open, semi-connected, fibropitted network of fibres and intervening spaces, without tegillum. Intra-fibrilla pits are generally ellipsoid and ca. 0.3 - 2.0Ám in maximum diameter. Most processes are simple but some may be proximally joined or may bifurcate once at approximately two thirds of length. They are fibrous, without a central canal and may be sinuous, but are most often truncate. Proximal diameter about 40%, and minimum diameter about 20%, of length, more of less evenly spaced with a distance between 40% to 100% of length separating processes. Distribution is usually nontabular although a discontinuous alignment may sometimes partially delimit the cingulum. Processes range from ca. 5% to 20% of maximum diameter. Process complexes or enlarged processes sometimes occur at either the apex or antapex but often are absent. The mid-dorsal precingular archeopyle is both anteriorly and posteriorly dithigmate with rectilinear or weakly geniculate interseries boundaries. The geometry of the resulting steno-thetaform free operculum can be planate, camerate or fastigiate. The sulcus is sometimes indicated by a mid-ventral group of less robust processes but is other times obscure.
Dimensions: Maximum measurable diameter excluding processes 50(72.2)95Ám (based on 34 specimens), holotype 76Ám; length 63(74.4)95Ám (based on 23 specimens); width 50(68.5)82Ám (based on 19 specimens), holotype 76Ám; breadth 47(64)85Ám (based on 10 specimens), holotype 66Ám. Total range in process length 4-20Ám, minimum longest process on a single specimen 10Ám, usual process length 8- 16Ám, holotype 13- 18Ám.
Comparison: Exochosphaeridium insigne sp. nov. is most similar in size, wall structure, process morphology and operculum geometry to Fibrocysta lappacea, described from the lower Eocene of Alabama. The latter species differs by having apical and antapical protrusions of the endoblast that may be quite prominent and may themselves bear long processes. However, Drugg (1970) reported that these features are not always present at both poles and it seems possible that the two species are related. Matsuoka and Bujak (1988) described Operculodinium alsium from putative upper Miocene strata of the Bering Sea and tentatively synonomized their material with Operculodinium sp. I of Manum (1976), recorded from upper Eocene sediments of the Norwegian-Greenland Sea. Exochosphaeridium insigne is here considered conspecific with Manum"s informal taxon. However, based on our observations of the holotype and other specimens of Operculodinium alsium, Exochosphaeridium insigne differs from that species in having proximate luxuriae comprising a coarse fibropitted network rather than microalveolate spongy luxuriae. The processes of Operculodinium alsium are distally aculeate while those of Exochosphaeridium insigne are distally truncated and lack aculeae. There is also a significant difference in size and processs length in the two species. Operculodinium alsium is smaller, having a maximum reported diameter of 62Ám and maximum process length of 7Ám, as compared with 95Ám and 20Ám for Exochosphaeridium insigne. (See Head 1994a, for further discussion of Operculodinium alsium).
The new species differs from Operculodinium centrocarpum in having coarser fibropitted luxuriae with intra-network pits up to 4Ám; it is also larger, and lacks distally aculeate processes and a deltatorm operculum. It differs form Exochosphaeridium bifidum in a similar way with respect to wall structure and process morphology and additionally lacks the apical tuft complex characteristic of that species.
Exochosphaeridium brevispinosum differs from the Exochosphaeridium insigne in having processes that are cylindrical, probably hollow and distally denticulate.
Occurrence: Lower Miocene in the Salisbury Embayment (DN2).
Holotype: Plate 3, figs. 5,6, 8- 10
Locus typicus: the Popes Creek Section, Potomac River, Popes Creek, Charles County, Maryland.
Type locality: The lower Popes Creek Sand Member of the Calvert Formation.
Original diagnosis: de Verteuil and Norris, 1996, p. 116: Exochosphaeridium insigne
Cysts intermediate, proximochorate and spherical. Autoblast comprising homogeneous pedium ca. 0.5Ám thick, and dense, fibropitted luxuriae 2.0 - 4.0Ám thick with evenly distributed, nontabular, fibrous, truncate, distally truncated processes. Archeopyle simple precingular with a distinctive theta-camerate to thetafastigiate free operculum.
Original description: de Verteuil and Norris, 1996, p. 116: Exochosphaeridium insigne
The proximate luxuriae form an open, semi-connected, fibropitted network of fibres and intervening spaces, without tegillum. Intra-fibrilla pits are generally ellipsoid and ca. 0.3 - 2.0Ám in maximum diameter. Most processes are simple but some may be proximally joined or may bifurcate once at approximately two thirds of length. They are fibrous, without a central canal and may be sinuous, but are most often truncate. Proximal diameter about 40%, and minimum diameter about 20%, of length, more of less evenly spaced with a distance between 40% to 100% of length separating processes. Distribution is usually nontabular although a discontinuous alignment may sometimes partially delimit the cingulum. Processes range from ca. 5% to 20% of maximum diameter. Process complexes or enlarged processes sometimes occur at either the apex or antapex but often are absent. The mid-dorsal precingular archeopyle is both anteriorly and posteriorly dithigmate with rectilinear or weakly geniculate interseries boundaries. The geometry of the resulting steno-thetaform free operculum can be planate, camerate or fastigiate. The sulcus is sometimes indicated by a mid-ventral group of less robust processes but is other times obscure.
Dimensions: Maximum measurable diameter excluding processes 50(72.2)95Ám (based on 34 specimens), holotype 76Ám; length 63(74.4)95Ám (based on 23 specimens); width 50(68.5)82Ám (based on 19 specimens), holotype 76Ám; breadth 47(64)85Ám (based on 10 specimens), holotype 66Ám. Total range in process length 4-20Ám, minimum longest process on a single specimen 10Ám, usual process length 8- 16Ám, holotype 13- 18Ám.
Comparison: Exochosphaeridium insigne sp. nov. is most similar in size, wall structure, process morphology and operculum geometry to Fibrocysta lappacea, described from the lower Eocene of Alabama. The latter species differs by having apical and antapical protrusions of the endoblast that may be quite prominent and may themselves bear long processes. However, Drugg (1970) reported that these features are not always present at both poles and it seems possible that the two species are related. Matsuoka and Bujak (1988) described Operculodinium alsium from putative upper Miocene strata of the Bering Sea and tentatively synonomized their material with Operculodinium sp. I of Manum (1976), recorded from upper Eocene sediments of the Norwegian-Greenland Sea. Exochosphaeridium insigne is here considered conspecific with Manum"s informal taxon. However, based on our observations of the holotype and other specimens of Operculodinium alsium, Exochosphaeridium insigne differs from that species in having proximate luxuriae comprising a coarse fibropitted network rather than microalveolate spongy luxuriae. The processes of Operculodinium alsium are distally aculeate while those of Exochosphaeridium insigne are distally truncated and lack aculeae. There is also a significant difference in size and processs length in the two species. Operculodinium alsium is smaller, having a maximum reported diameter of 62Ám and maximum process length of 7Ám, as compared with 95Ám and 20Ám for Exochosphaeridium insigne. (See Head 1994a, for further discussion of Operculodinium alsium).
The new species differs from Operculodinium centrocarpum in having coarser fibropitted luxuriae with intra-network pits up to 4Ám; it is also larger, and lacks distally aculeate processes and a deltatorm operculum. It differs form Exochosphaeridium bifidum in a similar way with respect to wall structure and process morphology and additionally lacks the apical tuft complex characteristic of that species.
Exochosphaeridium brevispinosum differs from the Exochosphaeridium insigne in having processes that are cylindrical, probably hollow and distally denticulate.
Occurrence: Lower Miocene in the Salisbury Embayment (DN2).