MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 41 



diameter of central body 34-68^, length of processes up to 26[x. Number of speci- 

 mens measured, 16. 



Remarks. The Cenomanian specimens greatly resemble those of Deflandre & 

 Cookson (1954, 1955) from the Lower Eocene of Australia, except that they are 

 smaller. H. crassipellis as illustrated by Maier (1959) is very different and cannot 

 be included within this species. 



Hystrichosphaera perforata sp. nov. 



PI- 5, fig- 7 

 Derivation of name. Latin, perforatus, perforated — with reference to the 

 perforate distal margins of the processes. 



Diagnosis. A species of Hystrichosphaera with smooth surfaced central body 

 bearing both gonal and sutural processes. Processes either tri- or tetra-linguate, 

 cylindrical and open with net-like perforations distally, or taeniate, being bi- or 

 trifurcate distally. Medial branching of processes may occur. Tabulation typical 

 of genus with plate 6" having a triangular outline. 



Holotype. B.M.(N.H.) slide ¥.51983(1). 85 feet above base of London Clay ; 

 Sheppey, Kent. 



Dimensions. Holotype : diameter of central body 40- 5 by 50, length of processes 

 up to 26[x. Range : diameter of central body 28-50^, length of processes i^-26\i. 

 Number of specimens measured, 4. 



Description. H. perforata sp. nov. is characterized by two types of processes : 

 (1) gonal processes being open, cylindrical with tri- or tetra-linguate margins and 

 possessing a triangular cross-section, and (2) taeniate processes being sutural in 

 position. The processes are united by proximal membranes, of varying height, 

 often with serrate edges, running along the plate boundaries. The open gonal 

 processes are strongly fenestrate distally on the secae and occasionally along their 

 length. A few of the processes are similar to those of H. ramosa var. ramosa in 

 being closed distally. Each seca is usually distally bifid. The sutural processes are 

 perforate distally where they bi- or trifurcate, and sometimes medially. 



Remarks. Two specimens of H. ramosa which were recorded by Gerlach (1961) 

 possessed processes perforate distally and along their length. All the processes of 

 these two specimens are, however, closed and the perforations are in the form of 

 small circular holes and not net-like as in H. perforata. H. porosa (Manum & 

 Cookson 1964) from the Upper Cretaceous of Canada possesses similar, but shorter 

 and broader, perforate processes and a characteristic reflected tabulation— ri', 5", 

 5c, 5'". I""- 



