MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 67 



Holotype. B.M.(N.H.) slide ¥.51740(1). Metropolitan Water Board Borehole 

 No. 11 at 43-25 feet depth, London Clay ; Enborne, Berkshire. 



Dimensions. Holotype : diameter of central body 18 by 19-5^, length of proces- 

 ses 9-12- 5[i., breadth of processes up to 2jx, length of acuminate processes 6-8[x, 

 number of processes 25 (and two acuminate processes) . Range : diameter of central 

 body n-20[x, length of processes 6-i^\i. Number of specimens measured, 5. 



Description. The processes show a variation in outline and nature of distal 

 margin which can be circularly to ovoidal, serrate, undulose or aculeate. The 

 distal extremities of the processes are usually considerably expanded, up to I3(x wide. 

 The length of the processes vary from one-third to two-thirds of the diameter of the 

 central body. Besides the tubiform process there is quite often a small number of 

 short, closed processes, as on the holotype. The latter are undoubtedly sulcal 

 processes. An apical archaeopyle is present surrounded by 6 processes, the reflected 

 tabulation probably being that of this genus. 



H. latirictum sp. nov. has been recorded from the London Clay of Enborne and of 

 Whitecliff Bay, Isle of Wight. 



Remarks. The size of H. latirictum sp. nov., in combination with the tubiform 

 processes, is quite characteristic. Polysphaeridium paulinae from the Middle 

 Jurassic of France (Valensi 1953) is similar in form but smaller with more processes, 

 the processes being not greater than one-third of the diameter of the central body. 

 It is possible that this species may result from misinterpretation of representatives 

 of the genus Stephanelytron : the holotype, kindly lent by Prof. Deflandre for 

 examination (in 1962), is at depth in flint and cannot be seen in full detail. Hystri- 

 chospheres with tubular processes are not otherwise known from the Middle Jurassic. 



1839 

 1842 

 1844 

 1848 

 1851 



?I934 

 1935 

 1937 



?i940 



?I955 



?ig63 



1964 



Hystrichosphaeridium recur vatutn (White) 



Xanthidium tubiferum (Ehr.) : Reade, pi. 9. figs. 6, 9. 



Xanthidium tubiferum palmatum White : 39, pi. 4, div. 3, fig. 12. 



Xanthidium tubiferum palmatum White ; White, pi. 8, fig. 11. 



Xanthidium palmatum White ; Bronn : 1375. 



Spiniferites palmatus (White) Mantell : 251, text-fig. 79. 



Hystrichosphaera tubifera (Ehr.) ; Deflandre, text-fig. 11. 



Hystrichosphaera tubifera (Ehr.) ; Deflandre : 15, pi. 7, fig. 10, ?n. 



Hystrichosphaeridium tubiferum (Ehr.) ; Deflandre : 96, pi. 13, fig. 2 ; (pi. 12, fig. 14 ; 



pi. 13. fig- 4)- 

 Hystrichosphaeridium recurvatum (White) Lejeune-Carpentier : 221, text-fig. 6. 

 Hystrichosphaeridium tubiferum (Ehr.) ; Valensi : 592, pi. 4, fig. 2 ; pi. 5, fig. 8. 

 Hystrichosphaeridium recurvatum (White) ; Gorka : 57, pi. 8, fig. 8 ; text-pl. 6, fig. 5. 

 Hystrichosphaeridium recurvatum (White) ; Sarjeant : 173. 



Emended diagnosis. Sub-spherical central body with moderate number of 

 slender tubiform processes. Length of latter between that of radius and diameter of 

 central body. Processes open distally, terminating with a few short orthogonal or 

 recurved spines. 



