5o MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Achomosphaera ramulifera var. perforata nov. 

 PI. 5, figs, i, 4 



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

 perforate nature of the processes. 



Diagnosis. A variety of A. ramulifera with gonal processes fenestrate proximally 

 and sometimes distally. 



Holotype. B.M.(N.H.) slide ¥.51764(1). 14 feet above base of London Clay ; 

 Whitecliff Bay, Isle of Wight. 



Dimensions. Holotype : diameter of central body 33 by 42^, length of processes 

 i6-i8[j.. Range : diameter of central body 33-56^, length of processes 15— 26jjl. 

 Number of specimens measured, 3. 



Remarks. The forms placed in A. ramulifera var. perforata differ from the 

 typical A. ramulifera by the presence of perforate processes. This characteristic 

 was not thought distinctive enough to justify the creation of a new species. 



This variety occurs infrequently in the London Clay (Ypresian) of England. 



Achomosphaera alcicornu (Eisenack) 

 PI- 5, ng. 3 



1954. Hystrichosphaeridium alcicornu Eisenack : 65, pi. 10, figs. 1, 2 ; text-fig. 5. 

 1 961. Hystrichosphaeridium alcicornu Eisenack : Gerlach : 188-189, pi- 28, fig. 7. 



Description. The London Clay specimens are very similar to H. tertiaria 

 (Eisenack & Gocht) and differ only in the absence of clearly defined plate boundaries. 

 A precingular archaeopyle is present. That the archaeopyle is precingular is 

 determined by its shape and the presence of 5 surrounding processes. The apical 

 process and the cingular processes are typically branched. As in all species of 

 Achomosphaera only gonal processes are present. The occasional specimen in the 

 London Clay is slightly granular and some possess processes that are perforate 

 distally. 



Material (figured). B.M.(N.H.) slide ¥.51765(1). Metropolitan Water Board 

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



Dimensions. Figured specimen : diameter of central body 54 by 54[x, length of 

 processes 28-40^. Range : diameter of central body 49-66^, length of processes 

 24-46PL Number of specimens measured, 4. 



Remarks. The stratigraphic range of A. alcicornu is from the Eocene (Ypresian) 

 to the Middle Miocene (Gerlach 1961). 



