88 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Holotype. B.M.(N.H.) slide ¥.51749(1). 275 feet above the base of London 

 Clay ; Whitecliff Bay, Isle of Wight. 



Dimensions. Holotype : diameter of central body 44 by 54^, length of processes 

 i8-26[x. Range : diameter of central body 44-98^, length of processes 16-42}/. 

 Number of specimens measured, 7. 



Description. Haplotabular archaeopyle and tabulation characteristic of the 

 genus Cordosphaeridium. The number of processes per plate area is one, but 

 occasionally a fine subsidiary process may be present. Fine processes also occur in 

 the sulcal region. Both the endophragm and periphragm are extremely thin, 

 especially the latter when forming the processes. The wall of the processes is 

 smooth or fibrous ; in the former the fibrils are only faintly developed. Whether 

 or not the processes are always fenestrate is difficult to determine, even at high 

 magnification, on account of the thinness of the periphragm. The processes rarely 

 exceed half the diameter of the central body ; they are up to I0[j. wide meridionally 

 and distally extremely expanded. Adjacent processes are occasionally united 

 distally. 



C. exilimurum has been recorded throughout the London Clay of England. 



Remarks. No other described species possesses fine, often perforate processes 

 with an apical haplotabular archaeopyle and tabulation 1', 6", 6c, 6'", 1"" and a 

 variable number of sulcal processes. ?C. cantharellum (Brosius 1963) is similar in 

 general form but possesses stronger, more cylindrical processes which are never 

 perforate or united distally, and often have a recurved distal margin. 



Cordosphaeridium latispinosum sp. nov. 



PI. 5, ng. 8 



Derivation of name. Latin, latus, broad ; spinosus, thorny — with reference to 

 the very wide processes present in this species. 



Diagnosis. Ellipsoidal central body having a finely striate periphragm from 

 which arise two types of processes : broad ovoidal to quadrate ones, closed or with 

 restricted distal opening, and slender oblate processes. Larger processes reflecting a 

 tabulation of 1', 6", 6'", 1"" ; smaller ones restricted to sulcal and cingulum regions. 



Holotype. B.M.(N.H.) slide ¥.51746(2). 173 feet above base of London Clay ; 

 Sheppey, Kent. 



Dimensions. Holotype : diameter of central body 56 by 6i(x, length of processes 

 up to 22(x. Range : diameter of central body 50-77^, length of processes 11-24}/., 

 width of broad processes up to 2j)x. Number of specimens measured, 5. 



Description. The broad processes of Cordosphaeridium latispinosum sp. nov. 

 are quadrate or ellipsoidal in cross-section proximally. They taper distally and have 

 a slightly fibrous wall which may be perforate with small lateral spines : the broad 

 processes are found on the apical, pre- and postcingular, posterior intercalary and 

 antapical plate areas. The slender processes appear to be sulcal or cingular processes. 



