60 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Description. The smooth periphragm of the central body and processes is some- 

 times slightly perforate but more commonly smooth. At the base of each process 

 there is a characteristic thickening of the endophragm, which is here reticulate. 

 Only four well preserved specimens have been observed, the number of wide 

 tubular processes ranging from 22 to 24, with 1 to 6 fine sulcal processes. The 

 antapical process is often distinctly wider than the other processes. The reflected 

 tabulation appears to be comparable to H. tubiferum. 



H. simplicispinum sp. nov. is present throughout the Barremian of Yorkshire. 



Remarks. In general appearance H. simplicispinum strongly resembles Cordo- 

 sphaeridium eoinodes but the fibrous periphragm is absent and the number of 

 processes is greater. 



The reflected tabulation of H. simplicispinum is probably the same as H. tubiferum, 

 but they differ in that the processes of the former are considerably more divided and 

 not so expanded distally. 



Hystrichosphaeridium patulum sp. nov. 

 PI. 10, fig. 5 



Derivation of name. Latin, patulus, broad and spreading — with reference of 

 the larger processes. 



Diagnosis. Spherical to sub-spherical central body, not exceeding 2551 in dia- 

 meter, possessing a smooth thin wall and bearing two types of processes. Both 

 types of same length and considerably expanded distally, one type much wider than 

 the other. Distal margin entire and undulating. Length of processes one-quarter 

 to one-half of the diameter of central body. Apical archaeopyle present. 



Holotype. B.M.(N.H.) slide ¥.51739(1). 7 feet above base of London Clay ; 

 Whitecliff Bay, Isle of Wight. 



Dimensions. Holotype : diameter of central body 11-5 by i4-5[x, length of 

 processes up to 5- 5{jl, number of processes 25. Range : diameter of central body 

 Ii-I9[i, length of processes 4-9^. Number of specimens measured, 8. 



Description. This species is characterized by its broad open processes, approxi- 

 mately 2[jl wide, and by the finer processes, up to ifx wide. The processes are tubi- 

 form with considerably expanded distal extremities measuring up to j\i across. The 

 number of processes can be up to 25. The apical archaeopyle has straight edges 

 obviously reflecting plate boundaries. 



Remarks. The small size of this species and the two types of processes are charac- 

 teristic. Its processes resemble shortened and sometimes widened processes of 

 H. tubiferum, and the number present is also similar. Some relationship may per- 

 haps be inferred between these two species. 



