MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



163 



processes. Such cingular processes are especially characteristic of the genus 

 Surculosphaeridium , and make specimen orientation comparatively easy. The form 

 of the processes and the exact distribution of the non-cingular processes, although 

 difficult to determine, indicate that this species does belong to this genus. 



Material (figured). B.M.(N.H.) slide ¥.51736(1). Lower Oxfordian, Dorset, 

 England. Upper Jurassic, England. 



Dimensions. Figured specimen : diameter of central body 37 by 47(jl, length of 

 processes up to 30fi. 



Surculosphaeridium longifurcatum (Firtion) 

 PI. 8, figs. 7, n, Text-figs. 43, 44 



1952. Hystrichosphaeridium longifurcatum Firtion : 157, pi. 9, fig. 1 ; text-fig. 1, H, K, L 



and M. 

 1963. Baltisphaeridium longifurcatum (Firtion) Downie & Sarjeant : 91, 



Description. A number of specimens have been found in the British Cenomanian 

 which appear to be comparable to Firtion's species from the Cenomanian of France. 



The central body is subspherical. The periphragm is smooth and gives rise to a 

 more or less constant 26 processes in a complete specimen. An angular archaeopyle 

 is commonly present, the detached apical region bearing 4 apical processes. The 

 processes are closed distally and are rather variable in form, being simple, lobate 

 foliate or digitate. Some of the processes, particularly those marking the cingulum, 

 are deeply branched. In the Upper Cenomanian particularly, the cingular processes, 

 each reflecting a cingular plate, may be completely subdivided. Thus there appears 

 to be two instead of one cingular process for each plate. 



Fig. 43. Surculosphaeridium longifurcatum (Firtion). Tabulation as reflected by the pro- 

 cesses. Left, top lateral view ; right, bottom lateral view. PF. 3042(1). x c. 800. 



