222 MKSOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



of M. sp. docs not form a concentric surrounding network but is restricted to an 

 equatorial zone, unlike that in M. reticulata. From the illustrations, Reissinger's 

 form looks identical to M. reticulata, which often shows a conspicuous absence of the 

 outer membrane in the equatorial zone when cingular processes are absent. 



Genus NEMATOSPHAEROPSIS Deflandre & Cookson 1955 : 268 



Emended diagnosis. Globular to ellipsoidal chorate cysts. Periphragm forms 

 gonal or sutural processes united proximally by sutural ridges or membranes. 

 Adjacent processes distally united by trabeculae. Archaeopyle precingular. 



Type species. Nematosphaeropsis balcombiana Deflandre & Cookson, 1955. 

 Miocene ; Australia. 



Discussion. The tabulation of Nematosphaeropsis is identical to that of Hystri- 

 chosphaera rarnosa. 



Nematosphaeropsis balcombiana Deflandre & Cookson 



z 955- Nematosphaeropsis balcombiana Deflandre & Cookson : 268, pi. 8, fig. 5. 



Discussion. Two specimens from the London Clay are attributed to N . bal- 

 combiana. They closely agree with the type material, the dimensions being : central 

 body, length 38-40(1, breadth 28-33^ ; process length io-22[x. The specimens were 

 found in sample Wh 6 from Whitecliff and En from Enborne. 



Genus CANNOSPHAEROPSIS O. Wetzel 1932 : 140 



Emended diagnosis. Ellipsoidal chorate cyst with precingular archaeopyle and 

 bearing branching or furcate processes like those of Hystrichosphaera in both struc- 

 ture and distribution, but without sutural ridges or septa connecting their bases as in 

 that genus. Processes interconnected distally by trabeculae. Endophragm and 

 periphragm in close contact between bases of processes. 



Type species. Cannosphaeropsis utinensis O. Wetzel 1932. U. Cretaceous ; 

 Baltic. 



Discussion. Evitt (1963) has pointed out that many species included within 

 Cannosphaeropsis (according to Deflandre's (1947) definition) significantly differ 

 from the type species. It is therefore proposed to restrict Cannosphaeropsis to 

 species possessing gonal and sutural processes allied with a precingular archaeopyle ; 

 species with intratabular processes and apical archaeopyle, formerly attributable to 

 Cannosphaeropsis, have been transferred to the genus Adnatosphaeridium. 



No attempt is made to reallocate species of Cannosphaeropsis where the species in 

 question have not been examined. 



