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Membranilarnacia reticulata
Membranilarnacia reticutata Williams and Downie, 1966c, p.220–221, pl.24, figs.4,6; text-fig.59.
Taxonomic senior synonym: Cannosphaeropsis (now Eatonicysta) ursulae, according to de Coninck (1969, p.43) and Gocht (1969, p.65). Lachkar and Masure in Fauconnier and Masure (2004, p.390) considered this to be a problematic species, but apparently also accepted the synonymy cited above.
Holotype: Williams and Downie, 1966, pl.24, fig.4; Bujak et al., 1980, pl.10, figs.3-4
Locus typicus: Sheppey, Kent, England
Stratum typicum: Early Eocene
Original diagnosis: Williams and Downie, 1966, p. 220
Ellipsoidal central body with intratabular processes, one per plate. Processes indicating a tabulation of 1-4", 6", 4c, 5""", 1"""". Cingular processes sometimes absent. Sulcal processes and posterior intercalary process present on some individuals. Processes cylindrical, solid, fibrous, united distally by a fine reticulate membrane totally or partially enclosing central body. Processes rarely exceeding 20 Ám in length.
Dimensions: Holotype: diameter of central body 42 by 43 Ám. Length of processes up to 26 Ám. Observed range: diameter of central body 35-44 Ám. Length of processes 7-24 Ám.
Original description: Williams and Downie, 1966, p. 221
The central body has a thin wall, smooth or slightly granular, comprising the endophragm. When an archaeopyle is present, the zigzag margin sharply delimits six rectangular plates, each bearing a process. The sulcal notch is usually clearly discernible. The process denoting the posterior intercalary plate is more commonly absent.
The fibrous processes rarely exceed two thirds of the diameter of the central body in length. They are generally simple and few in number, this being governed by the number of plates present. The size of the process may be a reflection of its position on the central body, the postcingulars often being smaller than the precingular processes. The cingulum appears to be slightly helicoidal.
The meshwork of the reticulate membrane is variable in size within an individual: it is finer nearer the process. The membrane is not unlike a closely woven net in structure, with numerous fine interconnecting orthogonal threads. The membrane may be restricted to distinct zones as in the figured specimen. There the processes of each series of plates are distally united and have few interconnecting links with processes of other plate series. This can be useful in orientation since it clarifies the position of the different plate series, and particularly the pre- and postcingulars.
Two variants of M. reticulata are recognized based on the arrangement of the processes. These are: Var. a. Reflected tabulation as in specific diagnosis but with no cingular processes. Sulcal processes may be present. This is the commoner of the two variants. Var. b. Tabulation as in specific diagnosis with cingular processes present, there being four in number.
Variability in M. reticulata also extends to the number of apical processes, some specimens having one, others having four. However since it is impossible to distinguish them when the archaeopyle is developed, the two forms are treated together as parts of the same species.
Affinities:
Williams and Downie, 1966, p. 221: Comparison of M. reticulata with other described forms suggests close affinity with Membranilarnax sp. O. Wetzel (1936), from the Upper Eocene of Germany. Reissinger (1950) figured a similar form which he simply termed a " hystrichosphere ", this also being from the Eocene of Germany. Unfortunately neither of these specimens have been preserved, and only Wetzel attempted a description, brief in the extreme, stating that the form was a spiny sphere within an outer shell; a description too succinct to be useful.
Taxonomic senior synonym: Cannosphaeropsis (now Eatonicysta) ursulae, according to de Coninck (1969, p.43) and Gocht (1969, p.65). Lachkar and Masure in Fauconnier and Masure (2004, p.390) considered this to be a problematic species, but apparently also accepted the synonymy cited above.
Holotype: Williams and Downie, 1966, pl.24, fig.4; Bujak et al., 1980, pl.10, figs.3-4
Locus typicus: Sheppey, Kent, England
Stratum typicum: Early Eocene
Original diagnosis: Williams and Downie, 1966, p. 220
Ellipsoidal central body with intratabular processes, one per plate. Processes indicating a tabulation of 1-4", 6", 4c, 5""", 1"""". Cingular processes sometimes absent. Sulcal processes and posterior intercalary process present on some individuals. Processes cylindrical, solid, fibrous, united distally by a fine reticulate membrane totally or partially enclosing central body. Processes rarely exceeding 20 Ám in length.
Dimensions: Holotype: diameter of central body 42 by 43 Ám. Length of processes up to 26 Ám. Observed range: diameter of central body 35-44 Ám. Length of processes 7-24 Ám.
Original description: Williams and Downie, 1966, p. 221
The central body has a thin wall, smooth or slightly granular, comprising the endophragm. When an archaeopyle is present, the zigzag margin sharply delimits six rectangular plates, each bearing a process. The sulcal notch is usually clearly discernible. The process denoting the posterior intercalary plate is more commonly absent.
The fibrous processes rarely exceed two thirds of the diameter of the central body in length. They are generally simple and few in number, this being governed by the number of plates present. The size of the process may be a reflection of its position on the central body, the postcingulars often being smaller than the precingular processes. The cingulum appears to be slightly helicoidal.
The meshwork of the reticulate membrane is variable in size within an individual: it is finer nearer the process. The membrane is not unlike a closely woven net in structure, with numerous fine interconnecting orthogonal threads. The membrane may be restricted to distinct zones as in the figured specimen. There the processes of each series of plates are distally united and have few interconnecting links with processes of other plate series. This can be useful in orientation since it clarifies the position of the different plate series, and particularly the pre- and postcingulars.
Two variants of M. reticulata are recognized based on the arrangement of the processes. These are: Var. a. Reflected tabulation as in specific diagnosis but with no cingular processes. Sulcal processes may be present. This is the commoner of the two variants. Var. b. Tabulation as in specific diagnosis with cingular processes present, there being four in number.
Variability in M. reticulata also extends to the number of apical processes, some specimens having one, others having four. However since it is impossible to distinguish them when the archaeopyle is developed, the two forms are treated together as parts of the same species.
Affinities:
Williams and Downie, 1966, p. 221: Comparison of M. reticulata with other described forms suggests close affinity with Membranilarnax sp. O. Wetzel (1936), from the Upper Eocene of Germany. Reissinger (1950) figured a similar form which he simply termed a " hystrichosphere ", this also being from the Eocene of Germany. Unfortunately neither of these specimens have been preserved, and only Wetzel attempted a description, brief in the extreme, stating that the form was a spiny sphere within an outer shell; a description too succinct to be useful.