MESOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 39 



Gorka (1963). H. cingulata is characterized by well developed crests beyond which 

 the gonal processes or thickenings do not protrude, the latter acting apparently only 

 as supporting structures. The processes may be either simple or may terminate with 

 a small bifurcation. The surface of the central body is smooth ; however the peri- 

 phragm forming the crests may be slightly reticulate. The reflected tabulation is 

 typical of the genus. 



H. cingulata has a stratigraphic range from the Cenomanian (England) to the 

 Pleistocene (Eastern Mediterranean). 



Material (Figured). Geol. Surv. Colin., slide PF.3039(i). Lower Chalk, H.M. 

 Geological Survey Borehole, Fetcham Mill, Surrey, at 730 feet depth. Upper 

 Cretaceous (Cenomanian). 



Dimensions. Figured specimen : diameter of central body 37 by 39fi, height of 

 crests up to i3[x. Range of Cenomanian specimens : diameter of central body 

 26-48^, height of crests up to I3jx. Number of specimens measured, 15. 



Hystrichosphaera cingulata var. reticulata nov. 

 PL 1, fig. 10 ; PI. 2, fig. 4 



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

 nature of the periphragm. 



Diagnosis. A variety of H. cingulata with central body composed of smooth 

 endophragm and strongly reticulate periphragm often somewhat thickened. Gonal 

 " processes " not protruding above sutural crests, processes acting more or less as 

 supporting structures for crests. Processes simple or terminating with small 

 bifurcation. 



Holotype. Geol. Surv. Colin., slide PF. 3039(2). Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 730 feet depth. Upper Cretaceous 

 (Cenomanian). 



Dimensions. Holotype : diameter of central body 40 by 55[jl, height of crests 

 up to i4fju Range : diameter of central body 33-59fx, height of crests up to \y\x. 

 Number of specimens measured, 12. 



Remarks. This variety strongly resembles H. cingulata (O. Wetzel) but the 

 central body has a strongly reticulate surface. Gorka (1963) states that many of the 

 French examples of H. cingulata are lightly punctate and so may well belong to 

 H. cingulata var. reticulata. 



H. cingulata var. reticulata occurs infrequently in the Middle and Upper Ceno- 

 manian of England. 



Hystrichosphaera crassimurata sp. nov. 



PI. 1, fig. 11 



Derivation of name. Latin, crassus, thick ; murus, wall — with reference to the 

 extreme thickening of the central body periphragm. 



