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Impletosphaeridium lumectum
Impletosphaeridium lumectum (Sarjeant, 1960) Islam, 1993
Holotype: Sarjeant, 1960, pl.6, fig.1
Locus typicus: Ringstead Waxy Clay 1 foot below the base of the Ringstead Coral Bed at the top of the cliffs at Osmington Mills, Dorset (grid reference 817736)
Stratum typicum: Late Oxfordian, Jurassic
Translation Courtinat, 1989: LPP
Original diagnosis: Sarjeant, 1960, p. 139: Baltisphaeridium lumectum
A species of Baltisphaeridium having an unornamented spheroidal shell, from which arise slender processes, simple, bifurcate or trifurcate, usually curved in some degree. The number of processes is such that 35 to 40 are seen around the shell periphery: their length is greater than two-thirds the shell diameter.
Original description: Sarjeant, 1960, p. 139: Baltisphaeridium lumectum
Shell dark yellowish brown in colour. The processes are of constant length. Near their tips they frequently bifurcate or trifurcate, the resultant branches not being of constant length on an individual process or between processes: equally frequently, however, they are simple.
Dimensions. Type specimen: overall diameter 60 Á, diameter of shell 25 Á, spines c. 17 Á long. Range: overall diameters 45 to 65 Á.
Remark: Courtinat, 1989, p.166: Cleistosphaeridium lumectum
SEM analysis indicates that this form possesses a (4AI(1a)) archaeopyle. The complete paratabulation formula could not be defined.
Affinities:
Sarjeant, 1960, p. 140: Baltisphaeridium lumectum
In the combination of form, length, and number of the spines, Baltisphaeridium lumectum differs from all other species described. Baltiphaeridium multifurcatum (Deflandre, 1937), from the Cretaceous of France, has processes similar in form but much shorter (less than one-quarter the shell diameter): in addition, the shell surface of this species is covered by a "vermicular ornamentation" lacking in B. lumectum. The specimens attributed to B. polytrichum (Valensi, 1947) by Downie, 1957, from the Upper Kimmeridgian of Dorset, have simple or bifurcate processes less than half the shell diameter in length, but similar in number: their resemblance to B. Iumectum is such that they would perhaps be better named Baltisphaeridium sp. aff. Iumectum than referred to B. polytrichum a species having entirely simple spines in much greater density (Valensi, 1947, 1953).
Holotype: Sarjeant, 1960, pl.6, fig.1
Locus typicus: Ringstead Waxy Clay 1 foot below the base of the Ringstead Coral Bed at the top of the cliffs at Osmington Mills, Dorset (grid reference 817736)
Stratum typicum: Late Oxfordian, Jurassic
Translation Courtinat, 1989: LPP
Original diagnosis: Sarjeant, 1960, p. 139: Baltisphaeridium lumectum
A species of Baltisphaeridium having an unornamented spheroidal shell, from which arise slender processes, simple, bifurcate or trifurcate, usually curved in some degree. The number of processes is such that 35 to 40 are seen around the shell periphery: their length is greater than two-thirds the shell diameter.
Original description: Sarjeant, 1960, p. 139: Baltisphaeridium lumectum
Shell dark yellowish brown in colour. The processes are of constant length. Near their tips they frequently bifurcate or trifurcate, the resultant branches not being of constant length on an individual process or between processes: equally frequently, however, they are simple.
Dimensions. Type specimen: overall diameter 60 Á, diameter of shell 25 Á, spines c. 17 Á long. Range: overall diameters 45 to 65 Á.
Remark: Courtinat, 1989, p.166: Cleistosphaeridium lumectum
SEM analysis indicates that this form possesses a (4AI(1a)) archaeopyle. The complete paratabulation formula could not be defined.
Affinities:
Sarjeant, 1960, p. 140: Baltisphaeridium lumectum
In the combination of form, length, and number of the spines, Baltisphaeridium lumectum differs from all other species described. Baltiphaeridium multifurcatum (Deflandre, 1937), from the Cretaceous of France, has processes similar in form but much shorter (less than one-quarter the shell diameter): in addition, the shell surface of this species is covered by a "vermicular ornamentation" lacking in B. lumectum. The specimens attributed to B. polytrichum (Valensi, 1947) by Downie, 1957, from the Upper Kimmeridgian of Dorset, have simple or bifurcate processes less than half the shell diameter in length, but similar in number: their resemblance to B. Iumectum is such that they would perhaps be better named Baltisphaeridium sp. aff. Iumectum than referred to B. polytrichum a species having entirely simple spines in much greater density (Valensi, 1947, 1953).