. Bulletin of the British Museum (Natural History), Geology. 72 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS Dimensions. Neotype : diameter of central body 35 by 35jjl, length of processes 22-25[A. Range : diameter of central body 34-55[i., length of processes 22-43(x. Number of specimens measured, 9. Description. In the specimens from the Cenomanian, the periphragm of the central body is smooth or very slightly granular. The processes are cylindrical for most of their length, with an expanded opening distally, the margin of which is developed into aculei and secae. The aculei and secae can be
. Bulletin of the British Museum (Natural History), Geology. 72 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS Dimensions. Neotype : diameter of central body 35 by 35jjl, length of processes 22-25[A. Range : diameter of central body 34-55[i., length of processes 22-43(x. Number of specimens measured, 9. Description. In the specimens from the Cenomanian, the periphragm of the central body is smooth or very slightly granular. The processes are cylindrical for most of their length, with an expanded opening distally, the margin of which is developed into aculei and secae. The aculei and secae can be simple or branched, erect or patulate, orthogonal or even recurved. Where the processes meet the central body there is often a clearly marked ring indicating the point of divergence of the endophragm and periphragm. The wall of the processes is smooth or faintly fibrous ; their length usually measures between the radius and the diameter of the central body. The small number of processes and the apical archaeopyle, when present, enable one readily to determine the tabulation of 0. complex as reflected by the position of the processes. Specimens of 0. complex have been examined from two other horizons. Examples from the Speeton Clay (Barremian) of Yorkshire are very similar to the forms illustrated by Eisenack (1958). The periphragm of the central body is often slightly granular and some of the processes are more deeply divided and show more variation than is usual in this species. 11 specimens were measured, the diameter of the central body being 35-62[x and the length of the processes 12>-A7V^- Specimens from the London Clay (Ypresian) strongly resemble the Cenomanian forms, the processes perhaps being a little stouter. Diameter of central body 2()-^S\x, length of processes 23-39(jl (6 specimens measured).. Fig. 14. OHgosphaeridium complex (White). A specimen from the Cenomanian, in lateral view, showing the angular apical archaeopyle and the distribution of the processes. X
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