igo 



MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Remarks. W. tenuavirgula var. crassoramosa does not merit raising to specific 

 level, on account of the frequent occurrence of forms transitional to W. tenuovirgula. 

 The extreme development of the secae (more correctly termed bars at this stage of 

 development) however is very distinctive. 



Wetzeliella (Wetzeliella) homomorpha Deflandre & Cookson 



1948. Hystrichosphaeridium geometricum Pastiels (pars) : 41, pi. 4, figs. 3, 5, 6, 7, 9, 10. 

 I 955- Wetzeliella homomorpha Deflandre & Cookson : 254, pi. 5, fig. 7 ; text-fig. 19. 



Discussion. The species W. homomorpha is restricted to forms having a peri- 

 phragm with rhomboidal, ovoidal or sub-circular outline and which lacks well 

 developed horns. The processes tend to be concentrated on the ambitus and are 

 generally closed distally. The archaeopyle is intercalary. Deflandre & Cookson 

 (1955) stated that none of the Australian examples contained the internal " cyst " 

 characteristic of Wetzeliella. Their " cyst " formed by the endophragm is in fact 

 present in the forms from the London Clay, but is easily overlooked, since it lies close 

 to and follows the outline of the pericoel. W. homomorpha is therefore a species of 

 Wetzeliella in which the periphragm and endophragm are almost in contact 

 throughout. 



Fig. 50. Wetzeliella (Wetzeliella) tennivirgula var. crassoramosa nov. 

 dorsal surface, showing simulate complexes. 



Tabulation of 



