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, 1"". Archaeopyle apical. 



Type species. Perisseiasphaeridium pannosum sp. nov. 



Remarks. This genus appears to be intermediate between Hystrichosphaeridium 

 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. 

 PL 3, fig. 5 ; PI. n, fig. 8 : Text-fig. 15 



Derivation of name. Latin, pannosus ragged — with reference to the ragged or 

 torn appearance of the infundibular processes. 



Fig. 15. Perisseiasphaeridium pannosum sp. nov. A specimen from the London Clay, 

 ventral view, showing the distribution of the processes. x c. 1000. 



