102 



MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Description. The processes are restricted to one per plate area and indicate a 

 reflected tabulation of 3', 6", 6c, 5'", ip, 1"" and 1-5S. The equatorial and sulcal 

 processes are frequently more slender than the others. Distally the processes often 

 have a margin bearing short bifid aculei. The length of the processes is about half 

 the diameter of the central body. The margin of the archaeopyle is interrupted on 

 the epitract by a short projection, the sulcal tongue (Evitt). This has a correspond- 

 ing sulcal notch on the hypotract. The number of sulcal processes varies from 1 to 5. 

 In some specimens the plates readily separate, save for the three apicals which have 

 never been observed as individual plates. 



H. tenuispinosum sp. nov. has only been recorded from the London Clay of England. 



Remarks. From the nature of the archaeopyle, the coarsely granular wall and 

 the tabulation, H. tenuispinosum is distinct from all previously described species. 



Homotryblium pallidum sp. nov. 



PI. 12, figs. 4, 6 ; Text-fig. 22 



Derivation of name. Latin, pallidus, pale — with reference to the rather light 

 colour of the central body after staining. 



Fig. 22. Homotryblium pallidum sp. nov. A specimen from the London Clay. Internal 

 view of the epitractal operculum ; slender acuminate ancillary processes are present. 

 X c. 950. 



