igj MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



margins are included since they are identical to W. homomorpha var. quinquelata in 

 outline, wall thickness and tendency for processes to be concentrated on the ambitus. 

 As is to be expected, intermediate forms exist between W. homomorpha and W. 

 homomorpha var. quinquelata. 



Occurrence. Eocene, London Clay ; Whitecliff and Enborne. 



Stratigraphic range. W. homomorpha var. quinquelata has previously been 

 recorded from the Ypresian of Belgium (Pastiels 1948) and the Upper Eocene of 

 Germany (Alberti 1961). 



Remarks. Pastiels (1948) stated that H. geometricum is represented by flattened 

 capsules, roughly pentagonal, of which one of the sides, sometimes concave, is 

 smaller. Unfortunately the name created by Pastiels was pre-occupied by Hystri- 

 chosphaeridium geometricum Deflandre 1942, for forms with a polygonal test from the 

 Palaeozoic (since transferred to Veryhacium). This was pointed out by Deflandre & 

 Cookson (1955), who in erecting W. homomorpha compared it to H. geometricum 

 (Pastiels) and concluded that the two were probably synonymous. However, in the 

 diagnosis of W. homomorpha, Deflandre & Cookson stated that the theca is polygonal, 

 more or less rounded. A detailed study of London Clay forms attributable to the W. 

 homomorpha-H. geometricum (Pastiels) complex has shown that there are two extreme 

 forms of common occurrence, firstly pentagonal forms, often with well developed 

 horns, and secondly ovoidal, sub-spherical or rhomboidal forms lacking horns. 

 The two forms can be readily separated, although intermediate types do occur. 



Pastiels figured, as within his species, types identical to the two extreme London 

 Clay forms, as well as intermediate specimens, although the holotype of H. geometri- 

 cum (Pastiels) is almost pentagonal and the accompanying description suggests that 

 specimens with a pentagonal outline were the more frequent in the Ypresian. It 

 therefore seems advisable to restrict W. homomorpha to the forms having sub-spheri- 

 cal, ovoidal or rhomboidal outline, whilst defining a variety, W. homomorpha var. 

 quinquelata, to include forms having a pericoel with pentagonal outline with or without 

 horns. This is a workable system in the London Clay and avoids too much infra- 

 specific variation going unheeded. 



Wetzeliella (Wetzeliella) ovalis Eisenack 

 PL 18, fig. 10 



1954. Wetzeliella ovalis Eisenack : 59, pi. 8, figs. 1-7. 



Discussion. The outline of the periphragm of London Clay specimens of W. 

 ovalis is variable ; usually it is oval to rhomboidal, but it can be sub-pentagonal, 

 with a fifth side tending to develop when there are two antapical horns. The angle 

 of the sides are developed into small horns, one apical, two lateral and one or two 

 antapical ; when there are two, the right antapical horn is always the longer. The 

 simple or branched processes are intratabular and are uniformly present over all the 

 surface of the pericoel, not as the type material where they are sparse on the dorsal 

 and ventral surfaces. The tabulation of W. ovalis is the same as that of W. articulata. 



