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Cyclonephelium distinctum ssp. laevigatum
Cyclonephelium distinctum ssp. laevigatum Mehrotra and Sarjeant, 1986
Now Circulodinium distinctum ssp. Iaevigatum. Originally Cyclonephelium distinctum ssp. Iaevigatum, subsequently (and now) Circulodinium distinctum ssp. laevigatum.
Holotype: Mehrotra and Sarjeant, 1986, pl.9, fig.2; text-fig.7a
Age:Valanginian
Original diagnosis: A subspecies of Cyclonephelium distinctum having a laevigate phragma surface between the processes.
Description: Proximate, cryptotabulate cyst having a laevigate phragma and numerous short, apparently nontabulate processes. Autoblast broadly ovoidal to rounded- subpolygonal. Apex frequently lost in archaeopyle formation ; without the apex, the cyst is somewhat broader than long. Sulcal notch to the left of centre on the ventral surface. The polygonality of the archaeopyle margin indicates 4 apical and 6 precingular paraplates, but the paratabulation is not otherwise indicated. Processes generally distributed, except that they are lacking from the central region of the ventral and dorsal surfaces. Processes solid, with capitate, oblate, bifid or briefly bifurcate distal ends. Length of processes consistently less than onetenth of the cyst diameter.
Holotype: Slide IPEP/PVD/45/5 (illustrated in pl. 8, fig. 2 ; text-fig. 7a). Paratype : slide IPEP/PVD/45/1 (illustrated in pl. 9, fig. 2). K.D. Malaviya Institute of Petroleum Exploration, Dehra Dun, India. Type locality: Periyavadavadi Shallow South India. well-l, Cauvery basin, Horizon: holotype and paratype : Claystone bed at 141.50- 143 m depth (core 45) ; Valanginian.
Dimensions: Holotype : width of the autoblast 63 μm (operculure lacking), process length 4-11 μm. Paratype with operculum attached: 86 x 86 jam (pl. 9, fig. 2). Range : autoblast width 62-86 μm, process length 2-19 μm. Twelve specimens measured.
Occurance: Moderate in cores 25, 31 (Aptian) 35, 37, 40, 42 (Barremian-Hauterivian) and high in 45 (Valanginian).
Remarks: The Indian forms correspond in most particulars with the Australian species described by Deflandre & Cookson (1955), though it should be noted that, since a redescription of the latter in modern terms in overdue, the species may be too broadly drawn. The autoblast ornamentation on the holotype of Cyclonephelium distinctum has been described as ~ distinctly punctate )) by Deflandre & Cookson (1955, p. 286). However, the numerous specimens of this species recorded from India do not show any autoblast ornamentation at magnifications attainable by the optical microscope. Our erection of a new subspecies, rather than a new variety, is justified not only on the basis of geographic isolation but also because the stratigraphic range of these forms in the Indian sediments (Valanginian - Aptian) is significantly different from that of the type subspecies, C. distinctum subsp, distinctum Deflandre & Cookson being known form Senonian strata.
Now Circulodinium distinctum ssp. Iaevigatum. Originally Cyclonephelium distinctum ssp. Iaevigatum, subsequently (and now) Circulodinium distinctum ssp. laevigatum.
Holotype: Mehrotra and Sarjeant, 1986, pl.9, fig.2; text-fig.7a
Age:Valanginian
Original diagnosis: A subspecies of Cyclonephelium distinctum having a laevigate phragma surface between the processes.
Description: Proximate, cryptotabulate cyst having a laevigate phragma and numerous short, apparently nontabulate processes. Autoblast broadly ovoidal to rounded- subpolygonal. Apex frequently lost in archaeopyle formation ; without the apex, the cyst is somewhat broader than long. Sulcal notch to the left of centre on the ventral surface. The polygonality of the archaeopyle margin indicates 4 apical and 6 precingular paraplates, but the paratabulation is not otherwise indicated. Processes generally distributed, except that they are lacking from the central region of the ventral and dorsal surfaces. Processes solid, with capitate, oblate, bifid or briefly bifurcate distal ends. Length of processes consistently less than onetenth of the cyst diameter.
Holotype: Slide IPEP/PVD/45/5 (illustrated in pl. 8, fig. 2 ; text-fig. 7a). Paratype : slide IPEP/PVD/45/1 (illustrated in pl. 9, fig. 2). K.D. Malaviya Institute of Petroleum Exploration, Dehra Dun, India. Type locality: Periyavadavadi Shallow South India. well-l, Cauvery basin, Horizon: holotype and paratype : Claystone bed at 141.50- 143 m depth (core 45) ; Valanginian.
Dimensions: Holotype : width of the autoblast 63 μm (operculure lacking), process length 4-11 μm. Paratype with operculum attached: 86 x 86 jam (pl. 9, fig. 2). Range : autoblast width 62-86 μm, process length 2-19 μm. Twelve specimens measured.
Occurance: Moderate in cores 25, 31 (Aptian) 35, 37, 40, 42 (Barremian-Hauterivian) and high in 45 (Valanginian).
Remarks: The Indian forms correspond in most particulars with the Australian species described by Deflandre & Cookson (1955), though it should be noted that, since a redescription of the latter in modern terms in overdue, the species may be too broadly drawn. The autoblast ornamentation on the holotype of Cyclonephelium distinctum has been described as ~ distinctly punctate )) by Deflandre & Cookson (1955, p. 286). However, the numerous specimens of this species recorded from India do not show any autoblast ornamentation at magnifications attainable by the optical microscope. Our erection of a new subspecies, rather than a new variety, is justified not only on the basis of geographic isolation but also because the stratigraphic range of these forms in the Indian sediments (Valanginian - Aptian) is significantly different from that of the type subspecies, C. distinctum subsp, distinctum Deflandre & Cookson being known form Senonian strata.