MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 59 



Dimensions. Holotype : diameter of central body 46 by 4J\l ; width of antapical 

 process 31^, length 35fx ; length of other processes 15-30E1. Number of processes 

 21. Range : diameter of central body 41-5411, length of processes i5-45jx. Num- 

 ber of specimens measured, 9. 



Description. The endophragm of the processes may be fibrous, but not strongly 

 so. The processes vary greatly in size and shape, this variation being continuous 

 between extremes of the range. The width of the processes on a specimen may vary 

 from i-5[x to 35^ ; the length of the processes is, however, more constant. The 

 largest process is usually the antapical, it being sub-conical to lagenate in shape. In 

 one specimen only a few of the larger processes are seen to give rise to two or three 

 parallel branches distally. The processes reflect a tabulation of 4', 6", 6c, 5'", ip, 

 1"" and 2-4S. 



H. deanei has been recorded from the Middle and Upper Cenomanian of Fetcham 

 Mill, Surrey. 



Remarks. H. deanei sp. nov. resembles H. stellatum (Maier) recorded from the 

 Albian and Cenomanian of Australia by Cookson & Eisenack (19626). It is similar 

 in the general form of the processes and the size of the central body, but the sub- 

 conical to lagenate processes, common in the British forms, appear to be absent. 

 The Australian form of H. stellatum does not appear to be comparable to Maier's type 

 material from the Oligocene of Germany. 



The form and the distal margins of the processes differentiate H. deanei from 

 H. tubiferum. The reflected tabulation, however, reveals a fairly close relationship 

 between the two species. 



Hystrichosphaeridium simplicispinum sp. nov. 

 PI- 9, ng. 3 



Derivation of name. Latin, simplicis, simple or straight and spinous, thorny — 

 referring to the rather simple nature of the processes. 



Diagnosis. Spherical central body composed of thin smooth endophragm and 

 periphragm, the latter forming the processes. Processes varying considerably in 

 size and are simple, tubiform, splaying out distally and terminate with denticulate or 

 secate margin. A number of fine sulcal processes. Apical archaeopyle usually 

 present. 



Holotype. B.M.(N.H.) slide ¥.51729(2). Speeton Clay, Shell West Heslerton 

 Borehole No. 1, Yorkshire at 39 metres depth. Lower Cretaceous (Middle Barre- 

 mian). 



Dimensions. Holotype : diameter of central body 36 by 43[x, length of processes 

 iy-26[i. Number of processes 23, plus 4 fine sulcal processes. Range : diameter of 

 central body 34-57[x, length of processes 8-31^. Number of specimens measured, 4. 



