158 I'I'PER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



Description. Test large, globular, inflated and coiled in a high trochospire ; 

 dorsal side convex, strongly inflated with the early chambers almost on the same 

 level and distinctly raised above those of the last whorl ; ventral side moderately 

 inflated ; equatorial periphery subcircular, distinctly lobate ; axial periphery 

 rounded ; the 18 chambers on the dorsal side increase slowly in size and are arranged 

 in 2,\ dextrally coiled whorls ; the last whorl is composed of 6, large, subglobular 

 chambers ; on the ventral side the chambers are 6, large, globular, strongly inflated 

 and increase slowly in size except for the third which is much smaller than the others ; 

 sutures on both sides almost straight, radial and strongly depressed ; umbilicus 

 small, deep and open (although it is filled with calcite growth and foreign material in 

 the figured specimen) ; aperture interiomarginal umbilical, an ovoid, large opening 

 with thick calcite growth around it ; wall calcareous, perforate ; surface smooth. 



Dimensions of holotype. 



Maximum diameter = 0-46 mm. 



Minimum diameter = 0-39 mm. 



Maximum thickness = 0-29 mm. (across the middle part of test) 



Variation. The main variation observed is in the degree of elevation of the 

 dorsal side which can be either weakly raised or coiled in a very high trochospire ; 

 coiling is random, with more tendency to dextral forms. 



Remarks. Globigerina arabica sp. nov. is distinguished from G. spiralis Bolli by 

 its much larger size, less elevated initial spire and more globular, inflated chambers. 

 In G. spiralis each whorl is higher than the following one and thus the dorsal side is 

 more or less conical in shape, while in G. arabica the first two whorls are more or less 

 in the same level but distinctly higher than the last. 



The presence of the peculiar calcite growth in the umbilicus and around the 

 aperture made it difficult to determine the taxonomic position of this species with 

 certainty. It is, therefore, included in Globigerina for the time being on the basis of 

 its other morphological features. 



Globigerina arabica has probably evolved from Globorotalia trinidadensis Bolli by 

 the elevation of the early whorls, the reduction of the rate of growth, and the confine- 

 ment of the aperture to an interiomarginal, umbilical position. Forms of G. trini- 

 dadensis with slightly raised early chambers are believed to be transitional to the 

 present species. G. arabica is also believed to have evolved into G. spiralis Bolli, as 

 substantiated by the morphological characters and stratigraphical distribution of 

 these two species. 



Holotype. P. 45570. 



Paratypes. P. 45571. 



Horizon and locality. Holo- and paratypes, from sample No. 30, Gebel 

 Owaina section. 



Stratigraphical range. Globigerina arabica sp. nov. ranges throughout the 

 Upper Danian part of the sections studied, (the Lower and Middle Danian being 

 missing). It does not cross the Danian-Middle Paleocene boundary. 



