74 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



The specimens attributed to H. complex by Baltes (1963, pi. 3, figs. 1-3) do not 

 belong in this species. In contrast, the forms he illustrates as H. tubiferum (pi. 2, 

 figs. 1-3, 5, 6) undoubtedly belong to Oligosphaeridium and probably to 0. complex. 



The holotype of 0. complex from the British Senonian illustrated by White 

 (1842, pi. 4, div. 3, fig. 11) cannot be traced. A neotype has therefore been chosen 

 from the Cenomanian of Surrey (England). 



Oligosphaeridium reticulatum sp. nov. 

 PL 7, fig. 10 



Derivation of name. Latin, reticulatus, net-like — with reference to the reticulate 

 or net-like appearance of the surface of the central body. 



Diagnosis. Subspherical central body composed of reticulate endophragm. 

 Periphragm confined to processes, smooth or slightly fibrous. Processes simple, 

 cylindrical, expanding distally and terminating in complicated aculeate or secate 

 margin. Archaeopyle apical. Number of processes in complete specimen never 

 exceeding 18. Inferred tabulation 4', 6", 5'", ip, 1"" and o-is. 



Holotype. Geol. Surv. Colin, slide PF. 3035(1). Lower Chalk, Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 840 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : diameter of central body 29 by 30^, length of processes 

 15-26^, number of processes 14. Range : diameter of central body 29-47^, 

 length of processes 14-26(1. Number of specimens measured, 5. 



Description. The reticulate endophragm appears to be granular at low magni- 

 fication, but at high magnification it is clearly seen to be finely reticulate. The 

 cylindrical processes expand slightly proximally, forming a characteristic circle 

 or oval on the surface of the central body. Distally they expand in the form of an 

 open funnel often having an extremely ragged margin. 



Remarks. 0. reticulatum sp. nov. is very similar to 0. complex, differing only in 

 the reticulate nature of the central body and the relative shortness of the processes. 

 It is very significant that the inferred tabulations are identical, indicating a close 

 phylogenetic relationship. 



Oligosphaeridium vasiformum (Neale & Sarjeant) 

 PL 9, fig 7 ; PL 10, fig. 1 ; Text-fig. 1 



1962. Hystrichosphaeridium vasiformum Neale & Sarjeant : 452, pi. 20, fig. 1 ; text-fig. 8b. 

 1965. Hystrichosphaeridium vasiformum Neale & Sarjeant ; Sarjeant, text-fig. 3C. 



Emended diagnosis. Sub-spherical to sub-quadrate central body composed of 

 thin, smooth endophragm and thicker pitted periphragm. Not more than 18 

 processes present, composed of smooth periphragm. Processes simple, tubiform and 

 expanding distally, distal margin bearing few spines. 



