8> MKSOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 



Baltcs (1963) illustrated two forms (A and B) of this species from the Albian of 

 Roumania. His species A has a central body diameter of 45-50^ and species B one 

 of approximately 25fz. In Britain it is interesting to note that the mean of the 

 central body diameter (34[x) falls midway between these two forms. Thus it seems 

 likely that L. siphoniphorum in Britain is represented in Roumania by two geo- 

 graphical subspecies, corresponding to Baltes' two forms, A and B. 



? Litosphaeridium inversibuccinum sp. nov. 

 PL 12, fig. 3 



Derivation of name. Latin, inversi, inverted ; buccina, trumpet — referring 

 to the trumpet-like shape of the processes. 



Diagnosis. Sub-spherical or ovoidal central body, not exceeding 20^1. in diameter, 

 with sub-conical processes. Processes open distally, with denticulate or aculeate 

 margin. Archaeopyle apical. 



Holotype. B.M.(N.H.) slide ¥.51744(1). Metropolitan Water Board Borehole 

 No. 11 at 83-25 feet depth, London Clay ; Enborne, Berkshire. 



Dimensions. Holotype : diameter of central body 17 by 19^, length of processes 

 7~9[x, number of processes 13. Range : diameter of central body n-igjx, length of 

 processes 4 — g\i. Number of specimens measured, 8. 



Description. The wall of the central body is usually thin, but thick walled 

 specimens have occasionally been encountered. The processes are not in connection 

 with the interior of the central body and seldom exceed 15. The larger processes are 

 sub-conical and may be up to iO[i wide at the base, rapidly decreasing in width to 

 approximately 1-5-2^, before expanding distally into a denticulate or aculeate 

 margin. In addition to these stout processes there are usually one or two slender 

 ones which are possibly closed distally. The latter are probably sulcal processes. 

 An apical tetragonal archaeopyle was seen in one specimen, the archaeopyle being 

 surrounded by 6 precingular processes. However the remaining tabulation is 

 obscure. 



Remarks. ? Litosphaeridium inversibuccinum sp. nov. is easily distinguishable 

 by its size and the form of its processes. It is tentatively placed in the genus 

 Litosphaeridium because it possesses the correct number of processes to give the 

 diagnostic tabulation of this genus, although the arrangement of the processes has, 

 as yet, not been elucidated and a detached apical region has not been observed. 

 The form of the processes and of the archaeopyle are both similar to those structures 

 in L. siphoniphorum. 



OTHER SPECIES 



The following species are here tentatively referred to the genus Litosphaeridium 

 on the basis of the number and type of processes : 



