184 MESOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 



Other individuals having a reduced apical horn and sometimes also a poorly 

 developed left antapical horn are intermediate to W. similis Eisenack. These are of 

 less frequent occurrence than the previously described forms. 



The forms recorded by Pastiels (1948) as Hystrichosphaeridium articulatum and 

 transferred to W. articulata by Eisenack (1954), are not in fact representatives of this 

 latter species. The diagnostic characteristics of W. articulata are the possession of a 

 well developed apical horn and two well developed antapical horns, usually unequal 

 in size. Pastiels' forms do not have this well developed second antapical horn and 

 are transferred to W. (W) symmetrica var. lobisca (see p. 196). 



Dimensions. Observed range in London Clay : outer shell length iii-i62|x, 

 breadth 64-105(1.. Number of specimens measured, 28. 



Occurrence. Eocene, London Clay ; Whitecliff, Studland, Sheppey and 

 Enborne. W. articulata has been recorded in Europe from the Lower Eocene to the 

 Middle Miocene. 



Wetzeliella (Wetzeliella) articulata var. conopia nov. 



PI. 18, fig. 5 



Derivation of name. Greek, konc-pos — gnat. 



Holotype. B.M.(N.H.) slide V. 51962. London Clay ; Sheppey, Kent, sample 

 SL.4. 



Dimensions. Holotype : outer shell length 132^, breadth i26[x, Capsule length 

 88[x. Observed range : outer shell, length i20-i56;x. Capsule, length 88-i05[i, 

 breadth 83-92^. Number of specimens measured, 4. 



Description. A variety of W. (W). articulata having processes that distally may 

 give rise to long aculei, often interconnected with aculei of adjacent processes. This 

 is an intermediate form to W. (W). leptavirgula sp. nov. It has been found in the 

 London Clay only at Sheppey. 



Wetzeliella (Wetzeliella) clathrata Eisenack 



PL 18, fig. 6 



1938. Wetzeliella clathrata Eisenack : 187, text-fig. 5. 



1954. Wetzeliella clathrata Eisenack ; Eisenack : 57, pi. 7, figs. 12-14 > text-fig. 2. 



1961. Wetzeliella clathrata Eisenack ; Gerlach : 153, pi. 25, fig. 6. 



1961. Wetzeliella clathrata Eisenack ; Evitt : 397, pi. 1, fig. 19. 



Discussion. A single specimen from the London Clay is attributed to W. (W). 

 clathrata. Many individuals that on initial examination appear to belong to W. 

 clathrata are really examples of W. (W). coleothrypta. W. clathrata is a distinctive 

 species whose processes are aligned in rows, immediately within the boundary of 

 a plate, forming simulate complexes. Adjacent processes are united distally by 

 perforate membranes restricted in width to a few microns ; these are the " lists " of 

 Eisenack. Tabulation is as in W. articulata and the reduced antapical horn lies to 

 the left of the mid-ventral line. 



