MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 77 



Remarks. 0. prolixispinosum sp. nov. is easily distinguishable from other species 

 by its elongate form and small number of processes with very characteristic distal 

 terminations. It should be noted that the basal wrinkles recorded in this species 

 have also been seen in Hystrichosphaeridium bowerbanki. 



At the base of the Cenomanian there have been found, together with normal 

 examples of 0. prolixispinosum, two specimens, which possess exactly the same 

 elongate central body and type of processes but there are present 22 and 25 processes. 

 This unusual number is caused by the presence of 6 cingular processes. It would thus 

 appear that 0. prolixispinosum is, in the Lower Cenomanian, rather an unstable 

 species and not until later in the Cenomanian does it settle down, the cingular 

 processes being absent. 



Because of the above variation this species is rather difficult to classify since 

 although the cingular processes are absent, it seems to be related to, or maybe even 

 evolved from, a type possessing these processes. Two other factors are that the 

 processes strongly resemble those found in H. bowerbanki and there may be 3 antapi- 

 cal processes present although this is uncertain. Until further information is avail- 

 able this species has been tentatively placed in the genus Oligosphaeridium because of 

 the absence of cingular processes. 



OTHER SPECIES 



The following species are here attributed to the genus Oligosphaeridium on the basis 

 of the number of processes and general form : 



Oligosphaeridium albertense (Pocock 1962). Lower Cretaceous ; Canada. 



Oligosphaeridium anthophorum (Cookson & Eisenack 1958). Upper Jurassic ; 

 Australia and Papua. 



Oligosphaeridium perforatum (Gocht 1959). Lower Cretaceous ; Germany. 



Oligosphaeridium reniforme (Tasch, McClure & Oftedahl 1964). Lower Creta- 

 ceous ; U.S.A. 



The following described species are doubtfully included in Oligosphaeridium on the 

 basis of the number and form of the processes: 



? Oligosphaeridium asterigerum (Gocht 1959). Lower Cretaceous ; Germany. 



? Oligosphaeridium coelenteratum (Tasch, McClure & Oftedahl 1964). Lower 

 Cretaceous ; U.S.A. 



~>. Oligosphaeridium dictyophorum (Cookson & Eisenack 1958). Upper Jurassic ; 

 Papua. 



? Oligosphaeridium dispare (Tasch, McClure & Oftedahl 1964). Lower Cretaceous ; 

 U.S.A. 



1 Oligosphaeridium irregular e (Pocock 1963 ; non Merrill 1895). Lower Cretaceous ; 

 Canada. 



1 Oligosphaeridium par adoxum (Brosius 1963). Oligocene ; Germany. 



