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Impletosphaeridium severinii
Impletosphaeridium severinii (Cookson and Cranwell, 1967) Liengjarern et al., 1980
Now Operculodinium. Originally Baltisphaeridium, subsequently Impletosphaeridium, thirdly (and now) Operculodinium.
Holotype: Cookson and Cranwell, 1967, pl.3, fig.1
Age: Eocene-Oligocene
Original description (Cookson and Cranwell, 1967):
Baltisphaeridium severinii Cookson and Cranwell sp. n. Plate 3, Figures 1-2
Description: Shell relatively large, approximately circular to ellipsoidal in outline, covered with densely arranged, tapering, unbranched processes, which gradually decrease in width rom broad, somewhat conical bases to over half their length, and the narrow rapidly to end in fine, frequently curved, very slender, apparently closed apices. Wall thin, usually obscured by the processes.
Dimensions of the leña Dura material: Holotype – overall diameter ca. 99 µm, shell diameter ca. 76 µm, wall thickness ca. 2 µm, processes mainly 10-16 µm long. Range in size of 20 specimens: Overall diameter ca. 75-114 µm, shell diameter ca. 55-85 µm, length if processes 10-25 µm.
Age and occurrence: Lower Tertiary, Leña Dura Formation, near Punta Arenas, Chile.
Holotype: Plate 3, figure 1; slide JSB-56:20 – single mount (Wild M20 99.5/36), at pesent in collections of L. M. Cranwell.
Comments: B. severinii appears to be closely related to B. whitei (Deflandre and Courteville, 1939), a Senonian species first described from French flints at Marong, and to B. nanum Cookson (1965a) from Upper Eocene deposits from Browns Creek, southwest Victoria. It differs from both species, however, in 1) the larger size and shape of the shell, which is 60-85 µm as compared with 23-34 µm in B. nanum and 56-60 µm in B. whitei, and in 2) the size and shape of the processes, particularly in respect to their broad-based appearances. Furthermore, the small opening occasionally seen in B. nanum has not been found in B. severinii.
Katz (1961) has reported redeposited B. pilosum (Ehrenberg) from the Argua Fresca Formation in Chile, which is of Eocene age, but this species has not been seen by us in the Leña Dura preparations.
Now Operculodinium. Originally Baltisphaeridium, subsequently Impletosphaeridium, thirdly (and now) Operculodinium.
Holotype: Cookson and Cranwell, 1967, pl.3, fig.1
Age: Eocene-Oligocene
Original description (Cookson and Cranwell, 1967):
Baltisphaeridium severinii Cookson and Cranwell sp. n. Plate 3, Figures 1-2
Description: Shell relatively large, approximately circular to ellipsoidal in outline, covered with densely arranged, tapering, unbranched processes, which gradually decrease in width rom broad, somewhat conical bases to over half their length, and the narrow rapidly to end in fine, frequently curved, very slender, apparently closed apices. Wall thin, usually obscured by the processes.
Dimensions of the leña Dura material: Holotype – overall diameter ca. 99 µm, shell diameter ca. 76 µm, wall thickness ca. 2 µm, processes mainly 10-16 µm long. Range in size of 20 specimens: Overall diameter ca. 75-114 µm, shell diameter ca. 55-85 µm, length if processes 10-25 µm.
Age and occurrence: Lower Tertiary, Leña Dura Formation, near Punta Arenas, Chile.
Holotype: Plate 3, figure 1; slide JSB-56:20 – single mount (Wild M20 99.5/36), at pesent in collections of L. M. Cranwell.
Comments: B. severinii appears to be closely related to B. whitei (Deflandre and Courteville, 1939), a Senonian species first described from French flints at Marong, and to B. nanum Cookson (1965a) from Upper Eocene deposits from Browns Creek, southwest Victoria. It differs from both species, however, in 1) the larger size and shape of the shell, which is 60-85 µm as compared with 23-34 µm in B. nanum and 56-60 µm in B. whitei, and in 2) the size and shape of the processes, particularly in respect to their broad-based appearances. Furthermore, the small opening occasionally seen in B. nanum has not been found in B. severinii.
Katz (1961) has reported redeposited B. pilosum (Ehrenberg) from the Argua Fresca Formation in Chile, which is of Eocene age, but this species has not been seen by us in the Leña Dura preparations.