MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



85 



Emended diagnosis. Spherical to sub-spherical fibrous central body bearing 

 small number of fibrous processes. Processes cylindrical, solid, erect, simple or 

 branched and distinctly digitate ; intratabular, one per plate area, number never 

 less than 19 or greater than 20. Archaeopyle apical, haplotabular, and reflected 

 tabulation that of the genus Cordosphaeridium. 



Holotype. Slide PH. 10. Geologisch-Palaontologisches Institut der Universi- 

 tat Tubingen. Lower Oligocene ; Germany. 



Material (figured). B.M.(N.H.) slide ¥.51746(1). 173 feet above base of 

 London Clay ; Sheppey, Kent. 



Dimensions. Holotype : diameter of central body jj\l, overall diameter i66(jl, 

 length of processes 46-52(1. Range : diameter of central body 45-90^, (mean 69(1.), 

 overall diameter 115-176^. ¥.51746(1) : diameter of central body 64 by 69^, 

 length of processes 33-37jx. Range of London Clay specimens : diameter of 

 central body 50-71(1, length of processes 20-43(1. Number of specimens measured, 

 12. 



Description. The central body is characterized by a thick two-layered wall 

 which is up to 2[x in thickness. The processes are strongly fibrous the fibres radiating 

 outwards from the base of the processes over the surface of the central body, and 

 when branched have a characteristic Y-shape. The single sulcal process is always 

 included within the cingulum series. 



Remarks. This species was originally described and figured by Eisenack (1938c) 

 as Hystrichosphaera cf. rantosa. Eisenack (1954) proposed a sub-species of Hystri- 

 chosphaeridium inodes to include these forms on the basis of similar wall structure. 

 The processes were described as solid, with fibrous branched endings, and the outer 

 layer of the wall of the central body could be thicker than the inner one. The 

 narrow hollow space in the interior of the processes at their base and passing through 

 to the inner wall layer that Klumpp observed in H. inodes was not perceived with 

 certainty by Eisenack for H. inodes gracilis. Eisenack (1954) noted and figured the 



Fig. 19. Cordosphaeridium gracilis (Eisenack). A specimen from the London Clay. 

 Left, apical view ; right, antapical view, by transparency. x c. 650. 



