2o 4 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Dimensions. Holotype — overall length 170^, breadth 93(0. ; length of apical 

 horn (tip missing) 55^, of antapical horn 34-5[i., of longer lateral horns 26^, length of 

 inner body, yoy., breadth 55^. Paratype — overall length 145(1, breadth 8oji. ; 

 length of apical horn, 47(x, of antapical horn, c.44^, of longer lateral horns c.3i[x ; 

 length of inner body c.^6[i, breadth c.5i[i.. These two specimens represent opposite 

 extremes of the observed range of variation. 



Description. The enclosing body has a basically cruciform outline, with a 

 distinctly oval shell enclosing, more or less tightly, an inner body of similar shape. 

 The lateral horns show no distinct notch, nor is a second, shorter antapical horn 

 developed ; however, the backward curve of the lateral horns and the lateral bump 

 on the antapical horn suggest affinity to species showing these features. 



The periphragm shows some degree of pitting, variable in degree and location but 

 usually especially dense on the apical horn. The inner body varies from smooth to 

 granular ; where it is smooth, the inner body becomes hard to distinguish and may 

 only be confirmed under phase contrast. (The holotype and paratype illustrate this 

 variation.) 



This species is relatively common in the Lower Barremian of the West Heslerton 

 Borehole : over 20 specimens were noted, of which the majority comprised either 

 detached apices or shells lacking an apex, complete shells being relatively infrequent. 

 Both holotype and paratype show incipient development of an archaeopyle. 



Remarks. Muderongia staurota sp. nov. is characterized by the morphology of its 

 shell processes. In contrast M. mcwhaei has a pronouncedly rhombic shell outline ; 

 proportionately longer and slimmer horns ; notched lateral horns and a second, short 

 antapical horn. M. simplex Alberti 1961, from the Lower Cretaceous (Hauterivian 

 to Valanginian) of Germany and Bulgaria, has short horns of almost equivalent 

 relative length, the lateral horns being blunt and notched, and a second antapical 

 horn being again developed. M. perforata Alberti 1961, from the Upper Cretaceous 

 (Turanian) of Germany, has very strong, thick horns, the second antapical horn 

 being especially pronounced. M. tetracantha (Gocht 1957), from the Lower Cretace- 

 ous (Hauterivian) of Germany, has in contrast extremely long and delicate horns ; 

 a second antapical horn is lacking, but the notching of the lateral horns is so deep asto 

 approach bifurcation into unequal branches. M. tomaszowensis Alberti 1961, from 

 the Lower Cretaceous (Valanginian) of Germany and Poland, has stubby apical and 

 antapical horns and blunt notched lateral horns. M. cruets Neale & Sarjeant 1962, 

 from the Lower Cretaceous (Hauterivian) of England, is extremely large (overall 

 length 250-325^) , with long axial horns and long lateral horns, the latter backswept 

 and not notched. 



Genus APTEODINIUM Eisenack 1958c 



Type species. A. granulatum Eisenack 1958c. Lower Cretaceous (Aptian) ; 

 Germany. 



