MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 65 



H. tubiferum (Ehrenberg) as illustrated by Lejeune-Carpentier (1940, text-fig. 5), 

 from Upper Cretaceous flint, is extremely similar to H. readei and could well belong 

 to the present species. 



Hystrichosphaeridium radiculatum sp. nov. 



PI. 7, fig. 8 ; PL 9, fig. 6 



Derivation of name. Latin, radicula, small root — with reference to the fibres 

 radiating from the bases of the processes. 



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

 endophragm and fibrous periphragm. Processes, approximately 30 in number, 

 composed of periphragm, fibrous, mainly hollow and open distally, simple tubiform 

 or dividing into 2 or 3 sub-parallel branches. Processes expanding slightly distally, 

 extremities of processes entire or denticulate. 



Holotype. Geol. Surv. Coll. slide PF.303i(i). Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 690 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : diameter of central body 36 by 37^, length of processes 

 I3-I7[x. Range : diameter of central body 3i-37[x, length of processes n-17^. 

 Number of specimens measured, 4. 



Description. The reticulate endophragm appears to be granular at first sight 

 before examination in detail. Along the lengths of the processes run fibrous strands 

 which continue on to the surface of the central body and are sometimes continuous 

 with similar strands from neighbouring processes. The depth of the furcation of the 

 processes varies considerably, from merely a slight distal furcation to where there 

 appears to be two separate processes in close proximity. A rather elongate apical 

 archaeopyle is present surrounded by 6 precingular processes. The distribution of 

 the remainder of the processes is difficult to determine precisely. 



This species is uncommon and has only been identified from the Upper Cenomanian. 



Remarks. H. radiculatum sp. nov. is closely related to H. mantelli differing in that 

 the branched processes are more common and the fibrils of the processes continue 

 across the surface of the central body. The reflected tabulation of the two species is 

 probably very similar. 



Hystrichosphaeridium cf. clavigerum (Deflandre) as illustrated by Lejeune-Carpen- 

 tier (1940, text-fig. 9), resembles H. radiculatum in size, form of the processes, and the 

 fibrous periphragm on the surface of the central body. However, the branching 

 processes characteristic of H. radiculatum, are absent. 



