104 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Callaiosphaeridium asymmetricum (Deflandre & Courteville) 

 PI. 8, figs. 9, 10 ; PI. 9, fig. 2 



1939. Hystrichosphaeridiimi asymmetricum Deflandre & Courteville : 100, pi. 4, figs. 1, 2. 



Description. This species, previously recorded only from the Senonian flints of 

 France, has now been observed in the Speeton Clay of Yorkshire (Hauterivian and 

 Lower and Middle Barremian) and in the Cenomanian of Surrey. All specimens 

 agree fairly well with the original description given by Deflandre & Courteville 

 (1939)- 



In the Barremian forms the large tubular processes tend to be considerably less 

 spinous than the Upper Cretaceous forms and more globular, especially along the 

 ribs. The term globular refers to small spherical spaces between the endophragm 

 and the periphragm. In the Cenomanian examples, the distal spines may measure 

 up to 20(j.. A noticeable feature in many of the British examples, not commented 

 on in the original description, is the elevation of the ribs joining the hypotractal 

 processes to form quite well developed septa. 



An archaeopyle is usually present, formed by the loss of the portion of epitract 

 just above the tubular cingular processes. The five postcingular processes are 

 joined by ribs forming a pentagon from which radiate ribs to the cingular processes. 

 Along one of these ribs are usually situated two processes — one posterior intercalary 

 and one sulcal. The apical region possesses a hexagon of 6 precingular processes and 

 an apical process which is sometimes deeply divided and arises from the centre of the 

 hexagon. The reflected tabulation therefore is : 1' (—2'), ? 6", 6c, $'" , ip, o"" and 

 o-is. 



Dimensions. Holotype : diameter of central body about 40[x, length of tabular 

 processes 22-34^. Range of Speeton Clay forms : diameter of central body 34-43^, 

 length of cingular processes ii-20jx. Number of specimens measured, 4. Range 

 of Cenomanian forms : diameter of central body 37-58^, length of cingular processes 

 io-32|i.. Number of specimens measured, 5. 



OTHER SPECIES HITHERTO PLACED IN H Y ST R I C H OSPH A E R I D I U M 



The following species formerly attributed to Hystrichosphaeridium Deflandre 1937 

 are here removed from this genus and referred to the following genera : 



Achomosphaera alcicornu (Eisenack 1954). Oligocene ; E. Prussia, USSR. 



Achomosphaera grallaeforme (Brosius 1963). Oligocene ; Germany. 



? Achomosphaera hirundo (Eisenack 1958). Lower Cretaceous ; Germany. 

 Hystrichosphaera leptoderma (Maier 1959). Oligocene ; Germany. 



? Hystrichokolpoma xiphea (Maier 1959). Oligocene ; Germany. 

 Cymatiosphaera membranacea (Philippot 1949). Oligocene ; Germany. 



