MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 69 



Diagnosis. Ovoidal central body with smooth or slightly granular surface. 

 Processes tubular, open distally, approximately equal in length to radius of central 

 body, terminating in a number of orthogonal or recurved spines. 



Holotype. B.M.(N.H.) slide ¥.51741(1). 85 feet above base of London Clay ; 

 Sheppey, Kent. 



Dimensions. Holotype : overall diameter 59 by 57^, diameter of central body 

 29 by 31 [x, length of processes i4-i8[z, width of processes up to 2\i, number of 

 processes 26. 



Description. The processes are relatively thick walled, the tubule being narrow 

 and sometimes constricted. At the bases of some of the processes there are small 

 proximal elevations or swellings. Distally the processes splay out into 2 to 7 

 spines or secae, up to 6jx long. An apical archaeopyle is usually present. The 

 tabulation reflected by the processes is that of Hystrichosphaeridium. 



Remarks. H. sheppeyense sp. nov. differs from H . recurvatum (White) in being 

 considerably smaller and possessing relatively short processes. The forms described 

 and figured by Deflandre & Cookson (1955) and by Evit (1961) are identical in all 

 respects except that the former, from the Senonian, is rather larger. Deflandre & 

 Cookson's figured specimen has an overall diameter of 90^, central body diameter of 

 44 by 51^ and processes 16-26(1 in length. 



Hystrichosphaeridium bowerbanki sp. nov. 

 PL 8, figs. 1, 4 



Derivation of name. After J. S. Bowerbank who was one of the first British 

 microscopists to record hystrichospheres from the Chalk, and the first to record them 

 from the Upper Greensand. 



Diagnosis. Ovoidal to elongate central body with smooth surface. Processes 

 thin-walled, tubular, open distally, sometimes widening considerably at their base, 

 and greater than half the central body diameter in length. They terminate in a 

 number of orthogonal or recurved spines. Apical archaeopyle usually present. 



Holotype. Geol. Surv. Colin, slide PF. 3033(1). Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey at 730 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : overall diameter 85 by j8y., diameter of central body 

 39 by 29[x, length of processes 24-26(1, number of processes 24. Range : overall 

 diameter 60-85(1, diameter of central body 29-40(0., length of processes 21-26. 

 Number of specimens measured, 5. 



Description. The central body is characteristically ovoidal to elongate. The 

 tubular processes are thin- walled and usually curved or bent to some extent. The 

 distal spines are 5 to 7 in number and are up to 6fx in length. The processes are 

 cylindrical for most of their length, 2-5 to 3^ wide and expand slightly distally to 

 about 4[x before giving rise to spines. Proximally the processes sometimes widen 



