MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 45 



Remarks. H. cornuta var. laevimura nov. differs from H. cornuta by possessing a 

 central body with a smooth wall and is separated from this species because of the 

 absence of intermediate forms with slightly granular walls. The apical bulge, 

 occasionally found in H. cornuta, is also found in this variety. The processes of the 

 latter are often more slender than those of H. cornuta but this feature is not charac- 

 teristic. 



This is a rare form, only recorded from the London Clay of England. 



Hystrichosphaera cf. cornuta Gerlach 



Description. The central body of this form is slightly granular and bears very 

 short gonal and sutural processes. The processes may be simple, bifurcate or 

 trifurcate. A moderate sized apical process is present. 



Material. B.M.(N.H.) slide ¥.51985(1). 25 feet above base of London Clay ; 

 Whitecliff Bay, Isle of Wight. 



Dimensions. ¥.51985(1) : diameter of central body 53 by 55^, length of pro- 

 cesses up to 9[i, length of apical process i8[i. Range : diameter of central body 

 3i-55fx, length of processes 4-9fx, length of apical process ii-i8fj.. Number of 

 specimens measured, 3. 



Remarks. H. cf. cornuta from the London Clay appears to be transitional to 

 H. speciosa (Deflandre 1934). The central body is less granular and the processes, 

 particularly the apical one, are shorter than is normal in H. cornuta. The apical 

 process, however, is similar in structure. 



Hystrichosphaera monilis sp. nov. 



PI. 5, ng. 2 



Derivation of name. Latin, monile, necklace or string of beads — with reference 

 to the appearance of the sutural crests. 



Diagnosis. A species of Hystrichosphaera possessing a spherical central body with 

 slightly granular surface. Processes short, sub-conical to cylindrical, closed, 

 simple or distally forked. Granules concentrated along proximal sutural crests. 



Holotype. B.M.(N.H.), slide ¥.51986(1). 78 feet above base of London Clay ; 

 Sheppey, Kent. 



Dimensions. Holotype : diameter of central body 36 by 38^, length of processes 

 up to iiji.. Range : diameter of central body 3i-46(x, length of processes up to ii[x. 

 Number of specimens measured, 5. 



