MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 189 



Holotype. B.M.(N.H.) slide ¥.51964(2). London Clay ; Sheppey, Kent, 

 sample 2. 



Dimensions. Periphragm, length 125-175(0. ; breadth 120-158(0.. Capsule, 

 length, 72-113(0. ; breadth 70-104.fi.. Number of specimens measured, 9. 



Description. W. tenuivirgula commonly has an outline similar to that of 

 W. articulata, with two well-developed antapical horns, although the left is absent in 

 some individuals. The apical and antapical horns are acuminate distally ; the 

 lateral horns are indented, denoting the position of a cingulum. The processes tend 

 to be graded, being longest furthest away from the horns. 



Occurrence. Eocene, London Clay ; Sheppey and Enborne. 



In some specimens the majority of the processes are regularly arranged just within 

 the plate boundary and form a simulate complex ; they may also arise nearer the 

 plate centre. The secae, besides uniting adjacent processes, often extend across the 

 plate, thus giving rise to a very loosely knit reticulum, totally different, in appear- 

 ance to that found in W. reticulata. Unconnected acuminate spines, up to 2-3(0. in 

 length, often arise from the interconnecting secae or trabeculae. The trabeculae 

 may be granular or smooth ; the secae are usually extremely fine and regular. 

 Processes of adjacent plates are not united. The pre- or postcingular plates may or 

 may not have processes on the side nearest the cingulum. The capsule almost fills 

 the pericoel, apart from the horns, and has a slightly granular wall. 



W. tenuivirgula differs from W. reticulata in the nature of the secae ; in the latter 

 species these are short and complexly anastomosing and are rarely unconnected. 



Wetzeliella (Wetzeliella) tenuivirgula var. crassoramosa nov. 

 PL 19, figs. 1, 5, 7 ; Text-fig. 50 



Derivation of name. Latin, crassus, thick, stout ; ramosus, branching ; 

 hence thick-branched. 



Holotype. B.M.(N.H.) slide ¥.51954(2). London Clay ; Whitecliff, sample 

 WC4. 



Dimensions. Holotype : outer shell length 125(0. ; breadth 122(0.. Capsule — 

 length 8o[jl ; breadth 71 ;x. Observed range : outer shell length 125-182(1 ; breadth 

 I22-i6o(ji. Capsule, length 80-144(0. ; breadth 71-103(0.. Number of specimens 

 measured, 8. 



Description. This differs from the typical W. tenuivirgula in the nature of the 

 distal branching of the processes ; the secae and trabeculae are much wider and 

 taeniate, the reticulum being much stronger as a result. The processes forming the 

 simulate complexes are often united by particularly wide taeniate secae (or bars) up 

 to 3jjt. in width. Frequently there are simple unconnected spines with blunt or 

 bulbous terminations branching off from the bars and trabeculae. In outline, the 

 outer shell lies between that of W. articulata and W. symmetrica, individuals with 

 an outline approaching the latter species predominating. 



Occurrence. Eocene, London Clay ; Whitecliff. 



