MESOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 103 



Diagnosis. Sub-spherical to ovoidal central body composed of thin inner endo- 

 phragm and granular periphragm. Processes of variable width, simple, tubiform, 

 forming a circle where they arise from central body. Archaeopyle epitractal and 

 processes reflecting generic tabulation. 



Holotype. B.M.(N.H.) slide ¥.51756(1). Metropolitan Water Board Borehole 

 No. 11, at 53 feet depth, London Clay ; Enborne, Berkshire. 



Dimensions. Holotype : diameter of central body 45 by 48^, length of processes 

 up to 25;jl Range : diameter of central body 40-49^, length of processes 16-34^. 

 Number of processes 5. Number of specimens measured, 5. 



Description. H pallidum sp. nov. exhibits similar tabulation to H. tenuispino- 

 sum of 3', 6", 6c, 5'", ip, 1"" with almost invariably only three sulcal plates. The 

 central body, which takes stain only slightly having a very thin wall, has granules up 

 to o-5ji. in height and o-5[x to 1 -5;x apart. The processes are cylindrical tubiform and 

 in length closely approach the radius of the central body. Distally they are variable, 

 in some specimens having an entire irregular margin, in others a serrate, aculeate or 

 digitate margin. Besides the tubiform processes there are often present 1 to 5 

 slender small acuminate processes. The latter can occur on the hypo- or epitract. 



This species has only been recorded from the London Clay of England. 



Remarks. H. pallidum differs from H. tenuispinosum in having a thinner wall, 

 generally broader processes with more variable distal margins, and a well marked 

 proximal circle where they arise from the central body. It also differs by having 

 some very slender acuminate processes. The specimens with processes having 

 entire circular or serrate margins appear to be closely related to Hystrichosphaeridium 

 choanophorum Deflandre & Cookson (1954) from the Miocene of Australia, although 

 Gerlack (1961) recognized what appears to be an apical archaeopyle in this species. 



Genus CALLAIOSPHAERIDIUM nov. 



Derivation of name. Greek, kallaion, cockscomb ; sphaera, ball — with 

 reference to the crests or ribs on the surface of the central body. 



Diagnosis. Chorate cysts with sub-spherical central body composed of two layers. 

 Processes intratabular and of two types : (i) cingular processes large and tubular, 

 open distally, and (ii) apical, precingular, postcingular and sulcal processes solid. 

 Antapical processes absent. Reflected tabulation inferred from arrangement of 

 processes is 1' (—2'), 6", 6c, 5'", ip, 0"" and o-is. Thickenings of periphragm 

 join all except cingular processes. Archaeopyle epitractal, suture just above 

 cingular processes. 



Type species. Hystrichosphaeridium asymmetricum Deflandre & Courteville 

 1939. Upper Cretaceous ; France. 



Remarks. The form of the processes, the epitractal archaeopyle and the absence 

 of antapical processes make this a very distinctive genus. The thickenings of the 

 periphragm joining the processes are also a noteworthy feature, though not peculiar 

 to this genus. 



