MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 179 



Holotype. B.M.(N.H.) slide ¥.51959(1). London Clay ; Enborne, sample 

 E 11. 



Dimensions. Holotype : diameter of central body 40-41^. Length of broad 

 processes up to 2ifi. Length of slender processes up to 24[x. Range of dimensions 

 observed : diameter of central body 44-56(1. Length of broad processes 20-30^, 

 width of broad processes 8-26fx. Length of slender processes i6-28[x, width of 

 slender processes usually i-3[x. Number of specimens measured, 3. 



Description. The broad processes of H. eisenacki var. turgidum may be sub- 

 conical and widely open distally or bulbose with a restricted opening that has a 

 serrate, commonly recurved, margin. Branching similar to that in H. eisenacki can 

 occur, but there are rarely more than one or two branches. The longer tapering 

 antapical process sometimes has very small tubules arising laterally and appears 

 minutely open distally. The broad processes give rise to a characteristic trapezoid 

 outline where they join the central body. The slender equatorial processes are 

 variable in number, generally being restricted to two per plate, with infrequently 

 three occurring. They are open with a digitate or serrate distal margin or they are 

 bifurcate. Often they arise in pairs, being united proximally for as much as £ of 

 their length. The tabulation is as in H. eisenacki with a reduced sixth precingular 

 plate and a large anterior sulcal plate. 



Occurrence. London Clay ; Enborne and Sheppey. 



Remarks. H. eisenacki var. turgidum differs from H. cinctum in the number of 

 cingular processes and the presence of a large anterior sulcal plate and process, and 

 from the typical form of H . eisenacki in the usual presence of broad processes that 

 have three or four branches distally. 



Hystrichokolpoma unispinum sp. nov. 

 PI. 17, figs. 6, 7 



Derivation of name. Latin, uni — one ; spina, spine. 



Diagnosis. Central body sub-spherical with thin smooth endophragm, continu- 

 ous beneath processes, and thin smooth periphragm. Processes formed from 

 periphragm and of two types, broad tapering lagenate, and buccinate more slender 

 processes. Reflected tabulation of 4', 6", 6g, 5'", ip, 1"" and at least 5s. Each 

 cingular plate possessing only one process. 



Holotype. B.M.(N.H.) slide ¥.51961(1), London Clay ; Whitecliff, sample WC 8. 



Dimensions. Holotype : diameter of central body 39 by 43(0.. Length of broad 

 processes up to 29fx, width up to 21 [i. Slender processes, length up to 26[x, width up 

 to 5fj.. Range of dimensions observed : diameter of central body 39-5 ifx. Length 

 of broad processes 21-29^1, breadth up to 2i[x. Equatorial processes, length i8-26[x, 

 breadth up to 5[x. Number of specimens measured, 3. 



