MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 99 



Diagnosis. Elongate central body with granular surface. Processes, moderate 

 in number, cylindrical, expanding slightly distally and terminating with serrate, 

 aculeate or truncated margin. 



Holotype. Geol. Surv. Colin, slide PF.3035(2). Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 840 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : length of central body 34(1, breadth 1451, length of 

 processes 12-16(1, number of processes 26. Range : length of central body 30-43(1, 

 breadth 14-20(1, length of processes 12-24(1. Number of specimens measured, 13. 



Description. The central body is composed of thin endophragm surrounded by 

 granular periphragm. The processes are composed of smooth periphragm, and have 

 an oval cross-section, there being characteristic oval areas on the surface of the central 

 body beneath the processes, marking the initial divergence of the periphragm from 

 the endophragm. The processes have fairly broad bases and taper distally before 

 expanding slightly before terminating. Distally the processes may be truncated, 

 terminate with one or two spines or splay out, the margin being serrate. The 

 number of processes normally varies between 20 and 31, but one specimen has been 

 observed with as many as 38. 



An apical archaeopyle is always present, surrounded by 6 precingular processes. 

 Medially there is a definite ring of 6 cingular processes and therefore 9-14 processes 

 on the hypotract. The arrangement of the hypotractal processes is difficult to 

 interpret ; however there appears to be either 3 or 6 antapical processes. The 

 number of sulcal processes appears to be 5-7. This species is therefore variable in 

 the number of processes it possesses and is able to have either one or two processes 

 per plate in certain areas. 



This species is present throughout the Cenomanian of England. 



Remarks. The only similar species is T. isocalamus (Deflandre & Cookson) 

 from the Lower Cretaceous of Australia. The figures of the Australian form 

 (Deflandre & Cookson 1955, pi. 2, figs. 7, 8) show that more processes are present than 

 in T. variecalamum and that the extremities of the processes are more uniformly 

 truncated. 



Tanyosphaeridium regulate sp. nov. 



PI- 3. %• 3 



Derivation of name. Latin, regularis, according to rule — with reference to the 

 regular arrangement of the processes. 



Diagnosis. Elongate central body with granular surface, bearing numerous 

 tubular, usually curved processes. Processes terminating with somewhat serrate 

 margin. 



Holotype. B.M.(N.H.) slide "^.51755(1). 270 feet above base of London Clay ; 

 Wbitecliff Bay, Isle of Wight. 



