MESOZOIC AND CAINOZOIC DINOFLAGELL ATE CYSTS 197 



antapical horn represented by slight protuberance on left antapical margin. Cap- 

 sule thick walled, often coarsely granular. Processes extremely short on ambitus of 

 periphragm and increasing in length further away from ambitus. Distally processes 

 bifid, aculeate, acuminate or evexate. 



Holotype. B.M.(N.H.) slide V. 51973. London Clay ; Sheppey, Kent, sample 2. 



Dimensions. Holotype : outer shell, length i03[x, breadth ioof*. Capsule, 

 length 73[x, breadth 7ijjl Observed range : outer shell, length o,6-i26[x, breadth 

 90-i25[x. Capsule, length 64-79^, breadth 63-84^. Length/breadth ratio of 

 pericoel 1-1 to i-i-i. Number of specimens measured, 7. 



Description. One of the diagnostic features of W. varielongituda are the processes. 

 The wall of the periphragm is up to i/2(jl in thickness, so that the slender processes 

 have only a minute central tubule, along their length. They are distally closed, 

 proximally open to the pericoel. The processes can be granular and are always 

 simple. The shortest processes occur on the ambitus of the pericoel and particularly 

 is this so on the lateral horns and epitract. It is these processes that can be acumin- 

 ate or evexate distally. The processes are regularly orientated in simulate complexes 

 or are irregular occurring within the complexes. Typical Wetzeliella tabulation is 

 decipherable, with the archeopyle intercalary. 



The horns of W. varielongituda tend to be broad and low, merging imperceptibly 

 with the lateral margins of the periphragm. This is especially so with the apical 

 horn. 



The capsule is sub-circular in outline, ellipsoidal in cross section and has a wall up 

 to 3*5{x thick. The wall often shows local thickening directly opposite the horns. 

 Distance of the capsule from the inner surface of the periphragm is variable. 



Occurrence. Eocene, London Clay ; Sheppey, Kent. 



Remarks. The nature of the processes, outline of the pericoel and structure of the 

 capsule readily distinguish Wetzeliella (W.) varielongituda from other species of 

 Wetzeliella. 



Sub-Genus WETZELIELLA (RHOMBODINIUM) Gocht 1955 



Diagnosis. A sub-genus of the genus Wetzeliella that does not possess processes 

 on the periphragm. Tabulation indistinctly shown apart from a transverse cingulum. 



Type species. Wetzeliella (Rhombodinium) draco (Gocht 1955). Oligocene ; 

 Germany. 



Wetzeliella (Rhombodinium) glabra Cookson 



PI. 20, figs. 9, 10 



1956. Wetzeliella glabra Cookson : 186, pi. 2, figs. 1-5. 



Discussion. Specimens of W. glabra from the London Clay differ from the type 

 material in having only one well developed antapical horn, the right. The left 

 antapical horn is, at the most, represented by a slight protuberance. The transverse 



