. Bulletin of the British Museum (Natural History), Geology. 78 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS Genus PERISSEIASPHAERIDIUM nov. Derivation of name. Greek, perisseia, abundance or surplus ; sphaera, ball—with reference to the rather superfluous sulcal and cingular processes. Diagnosis. Chorate cysts with sub-spherical central body composed of two membranes. Processes of two types : (i) larger, tubiform, open distally and intratabular ; one process per plate area, and (ii) smaller, closed processes restricted to sulcal and cingular regions. Tabulation reflected by tubiform processes
. Bulletin of the British Museum (Natural History), Geology. 78 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS Genus PERISSEIASPHAERIDIUM nov. Derivation of name. Greek, perisseia, abundance or surplus ; sphaera, ball—with reference to the rather superfluous sulcal and cingular processes. Diagnosis. Chorate cysts with sub-spherical central body composed of two membranes. Processes of two types : (i) larger, tubiform, open distally and intratabular ; one process per plate area, and (ii) smaller, closed processes restricted to sulcal and cingular regions. Tabulation reflected by tubiform processes 4', 6", 5'", ip, i"". Archaeopyle apical. Type species. Perisseiasphaeridiiim pannosum, sp. nov. Remarks. This genus appears to be intermediate between Hystrichosphaendium and Oligosphaeridium. It resembles the former in possessing both cingular and sulcal processes, but these are closed, and the latter since the tabular processes reflect a similar tabulation. It resembles Hystrichokolpoma in the presence of both tabular and closed processes, but the former are of a completely different type, being conical and covering most of the plate area. Also only 4 tabular postcingular processes are present in the genus Hystrichokolpoma whereas 5 are present in Peris- seiasphaeridium. Perisseiasphaeridium pannosum sp. nov. PI. 3, fig. 5 ; PI. II, fig. 8 : Text-fig. 15 Derivation of name. Latin, pannosus ragged—with reference to the ragged or torn appearance of the infundibular Fig. 15. Perisseiasphaeridium pannosum sp. nov. A specimen from the London Clay, ventral view, showing the distribution of the processes. x c. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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