94 MF.SOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 



width of processes i-i-5[x, number of processes 38-44. Number of specimens 

 measured, 3. 



Description. The central body has a smooth surface. The processes are 

 tubular with a thin wall. They widen slightly both proximally, at the junction with 

 the central body, and distally up to about 2jjl. The distal termination of a process 

 superficially strongly resembles that of Hystrichosphaeridium sheppeyi sp. no v., but 

 on closer examination the presence of spines has not been observed. The distal 

 margin is probably entire or slightly denticulate. The number of processes present 

 indicate that each precingular and postcingular plate area bears two processes. An 

 archaeopyle has not been observed with certainty. 



Remarks. This species is clearly differentiated from all other species by its size 

 and the number and type of processes present. It appears to be very similar to 

 Deflandre & Cookson's second series of specimens described as Hystrichosphaeridium 

 recurvatum (White) ; however the Australian examples of Lower Cretaceous age 

 seem to be larger, although the correct number of processes for the species is present. 

 Deflandre & Cookson (1955, pi. I, fig. 12) illustrate a specimen with seemingly similar 

 processes to the British Cenomanian examples. 



Polysphaeridium laminaspinosum sp. nov. 



PL 8, fig. 8 



Derivation of name. Latin, lamina, blade ; spinosus, thorny — referring to the 

 flattened blade-like appearance of the processes. 



Diagnosis. Spherical to sub-spherical central body composed of reticulate 

 endophragm. Processes numerous, approximately 36 in number, composed of 

 periphragm ; cylindrical, smooth and delicate, terminating in entire margin. 

 Characteristic circular impression occurring where process arises from central body. 



Holotype. Geol. Surv. Colin, slide PF.3052. Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 650 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : diameter of central body 27 by 2J\l, length of processes 

 ii-i5[jl, number of processes 36. Range ; diameter of central body 23-28^, length 

 of processes ix-ij\x. Number of specimens measured, 6. 



Description. The endophragm appears to be granular until examined under 

 high magnification when the reticulate nature becomes apparent. The processes are 

 broadly tubular, up to 5fz in width, usually flattened and are often bent. A few of 

 the processes are clearly truncated at their distal extremity, but most splay out 

 slightly and have a corrugated entire margin. A 6-sided apical archaeopyle has been 

 observed in one specimen. The number of processes present indicate that there are 

 two per plate. 



P. laminaspinosum is a rare species found throughout the Cenomanian of Fetcham 

 Mill, Surrey. 



