MESOZOIC AND CAINOZOIC DINOFLAGELL ATE CYSTS 



185 



Wetzeliella (Wetzeliella) coleothrypta sp. nov. 

 PL 18, figs. 8, 9 ; Text-fig. 47 



Derivation of name. Greek, koleos, scabbard, sheath ; thrypto, break. 



Diagnosis. Thin walled periphragm characteristic pentagonal outline with each 

 angle produced into horns, one apical, two lateral and two antapical ; left antapical 

 horn generally reduced. Pericoel totally enclosing endophragm. Processes arising 

 from periphragm, hollow, connecting with pericoel. Distally processes of individual 

 simulate complex united by finely perforate membrane assuming outline of under- 

 lying plate and extending over that plate as a replica of it. Processes commonly 

 absent from pre- and postcingular plates on side lying nearest to cingulum. Reflec- 

 ted tabulation of 4', 3a, 7", 5c, 5'", 2", 3-4S. 



Holotype. B.M.(N.H.) slide ¥.51753(3). London Clay ; Sheppey, Kent, 

 sample Sh.4. 



Dimensions. Holotype : periphragm length \Z2\l ; breadth iiojx. Capsule 

 length 6o.[x ; breadth 61-5(1. Observed range : outer shell length 1 12- 5-157^ ; 

 breadth 102- 5-142^. Capsule length 66-106(1 ; breadth 67-97(1. Processes up to 

 I5fx long. Number of specimens measured, 6. 



Description. The periphragm of W. coleothrypta has an outline approaching 

 W. similis on the one hand and W. articulata on the other. The right antapical horn 

 is invariably longer than the left, which is often represented by a small protuberance. 

 The apical horn has a pointed apex ; the lateral horns are indented distally due to the 

 transverse cingulum crossing from the dorsal to the ventral surface at these two 

 places. The slender, simple, or occasionally branched processes are intratabular, 



Fig. 47. Wetzeliella (Wetzeliella) coleothrypta sp. nov. Left, tabulation of ventral (upper) 

 surface of holotype ; right, tabulation of dorsal (lower) surface. S, sulcal plates ; PS, 

 posterior sulcal plate ; stippled areas show where processes are united distally by a membrane. 



