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Membranophoridium intermedium
Membranophoridium intermedium Stover and Hardenbol, 1994
Plate 4, Figures 24a-25b
Description
Proximate cysts with lenticular bodies having offset parasulcal notches. Endophragm thicker than periphragm, irregularly pitted and with or without small, subcircular unornamented areas; antapical margin without lobation. Periphragm thin, joined to the endophragm near the lateral margins of the ventral surface, thus leaving most of the ventral surface exposed, but covers the dorsal surface completely. Dorsal periphragm with penitabular arcuate and linear thickenings and ventral periphragm may be prolonged antapically forming usually two, generally bluntly rounded lobations. Archeopyle apical; operculum presumably tetraplacoid and contiguous although its constituent paraplates are undifferentiated, secate. Paratabulation indicated by principal archeopyle suture together with accessory sutures or notches as well as the dorsal periphragmal thickenings. These feature delimit six precingular paraplates of which paraplate 6"" is as wide as or slightly wider than 1" and peaked asymmetrically with the left side shorter than the right side. Dorsally, the middorsal precingular and postcingular paraplates and their laterally adjacent paraplates are delimited partly by penitabular arcuate thickenings that open adcingularly. The antapical paraplate is also delimited by a penitabular, arcuate feature that is open ventrally. Paracingulum expressed by transverse, discontinuous, short, linear thickenings on the dorsal surface. Parasulcus not delimited, but its anterior position is marked by the offset parasulcal notch. Size: intermediate; overall width 78 to 90Ám, body width 68 to
74Ám, pericoel 3.5 to 8.5Ám wide, antapical lobes up to 14Ám long.
Comparison
Membranophoridium intermedium contains features associated not only with other species of Membranophoridium, but also with some characteristics of Areoligera sentosa Eaton 1976. For example, the ventral aspect of M. intermedium closely resembles that of M. aspinatum and M. bilobatum Michoux 1985, whereas the dorsal aspect, with its penitabular arcuate and linear features, is not dissimilar to the dorsal configuration of A. sentosa. However, according to Eaton (1976) the dorsal penitabular structures on the latter species are...."sail-like, incised distal membranes....[with] pointed crests surmounted by erect or curved acuminate spines.", rather than thickenings. The dorsal surfaces of M. aspinatum and M. bilobatum are devoid of penitabular features.
Types
Holotype: Plate 4, figures 24a-b, Boom Composite Section sample at 51.90 meters (= Cored Reconnaissance Hole sample at a drill depth of 29.96 meters). Paratype: Plate 4, figures 25a-b, Boom Composite Section sample at 56.90 meters (= Cored Reconnaissance Hole sample at a drill depth of 24.86 meters).
Occurrence
Specimens of Membranophoridium intermedium occur fairly consistently in the Putte Member of the Boom Formation in the composite section between 24.78 and 49.70 meters. Above the 49.70 meter level, the species occurs sporadically to the 59.80 meter level. A single specimen was identified in the sample from the Terhagen Member at the 20.70 meter level.
Plate 4, Figures 24a-25b
Description
Proximate cysts with lenticular bodies having offset parasulcal notches. Endophragm thicker than periphragm, irregularly pitted and with or without small, subcircular unornamented areas; antapical margin without lobation. Periphragm thin, joined to the endophragm near the lateral margins of the ventral surface, thus leaving most of the ventral surface exposed, but covers the dorsal surface completely. Dorsal periphragm with penitabular arcuate and linear thickenings and ventral periphragm may be prolonged antapically forming usually two, generally bluntly rounded lobations. Archeopyle apical; operculum presumably tetraplacoid and contiguous although its constituent paraplates are undifferentiated, secate. Paratabulation indicated by principal archeopyle suture together with accessory sutures or notches as well as the dorsal periphragmal thickenings. These feature delimit six precingular paraplates of which paraplate 6"" is as wide as or slightly wider than 1" and peaked asymmetrically with the left side shorter than the right side. Dorsally, the middorsal precingular and postcingular paraplates and their laterally adjacent paraplates are delimited partly by penitabular arcuate thickenings that open adcingularly. The antapical paraplate is also delimited by a penitabular, arcuate feature that is open ventrally. Paracingulum expressed by transverse, discontinuous, short, linear thickenings on the dorsal surface. Parasulcus not delimited, but its anterior position is marked by the offset parasulcal notch. Size: intermediate; overall width 78 to 90Ám, body width 68 to
74Ám, pericoel 3.5 to 8.5Ám wide, antapical lobes up to 14Ám long.
Comparison
Membranophoridium intermedium contains features associated not only with other species of Membranophoridium, but also with some characteristics of Areoligera sentosa Eaton 1976. For example, the ventral aspect of M. intermedium closely resembles that of M. aspinatum and M. bilobatum Michoux 1985, whereas the dorsal aspect, with its penitabular arcuate and linear features, is not dissimilar to the dorsal configuration of A. sentosa. However, according to Eaton (1976) the dorsal penitabular structures on the latter species are...."sail-like, incised distal membranes....[with] pointed crests surmounted by erect or curved acuminate spines.", rather than thickenings. The dorsal surfaces of M. aspinatum and M. bilobatum are devoid of penitabular features.
Types
Holotype: Plate 4, figures 24a-b, Boom Composite Section sample at 51.90 meters (= Cored Reconnaissance Hole sample at a drill depth of 29.96 meters). Paratype: Plate 4, figures 25a-b, Boom Composite Section sample at 56.90 meters (= Cored Reconnaissance Hole sample at a drill depth of 24.86 meters).
Occurrence
Specimens of Membranophoridium intermedium occur fairly consistently in the Putte Member of the Boom Formation in the composite section between 24.78 and 49.70 meters. Above the 49.70 meter level, the species occurs sporadically to the 59.80 meter level. A single specimen was identified in the sample from the Terhagen Member at the 20.70 meter level.