86 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



archaeopyle and the operculum with a single process (plate 10, fig. 8). Gerlack 

 (1961) similarly noticed a " pylome " in H. inodes gracilis (plate 28, fig. 6). In 1963, 

 Eisenack transferred H. inodes and H. inodes gracilis to the new genus Cordosphae- 

 ridium. 



Because of the observed differences to C. inodes, namely the variable thickness of 

 the periphragm and endophragm, the absence of a narrow hollow space at the base 

 of the processes, the solid structure and peculiar branching of the processes, it is felt 

 that Eisenack's subspecies merits raising to the specific level. 



All of Eisenack's findings are verified in the London Clay specimens. Apart from 

 their larger size, Eisenack's and Gerlack's forms are identical with the London Clay 

 examples. 



Cordosphaeridium fibrospinosum sp. nov. 

 PI. 5, %• 5 



Derivation of name. Latin, fibra, fibrous ; spinosus, thorny — with reference to 

 the fibrous spines. 



Diagnosis. Ovoidal central body with wall up to o-5[x thick, composed of 

 smooth endophragm and fibrous periphragm. Processes fibrous, often very broad 

 and ovoidal in cross-section, walls perforate. Processes open distally, with entire or 

 undulose margin. One process per plate reflecting a tabulation typical of genus. 

 Archaeopyle apical haplotabular. 



Holotype. B.M.(N.H.) slide ¥.51747(1). Metropolitan Water Board Borehole 

 No. 11 at 53 feet depth, London Clay ; Enborne, Berkshire. 



Dimensions. Holotype : diameter of central body 63 by 6y\i, length of processes 

 i5-28[x, width of processes 5-25^. Range : diameter of central body 59-72^, 

 length of processes up to 39[x, width of processes up to 26[x. Number of specimens 

 measured, 5. 



Description. This species is characterized by fibrous, often perforate, processes 

 which can be latispinous. The perforations show no regularity in arrangement and 

 tend to be elongate. The cross-section of the processes is ovoidal or rarely cylindrical 

 and then only in the narrower processes. The lengths of the processes vary consider- 

 ably in different specimens but rarely exceed half the diameter of the central body. 

 It should be noted that in the broader processes, the width often exceeds the length. 



C. fibrospinosum sp. nov. has been recorded throughout the London Clay of 

 England. 



Remarks. The short, perforate processes, varying considerably in width but 

 often very wide, make C. fibrospinosum an easily distinguishable species. 



