IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 217 



quadrate, moderately lobate ; axial periphery subrounded ; chambers on the dorsal 

 side about 13, arranged in 2| dextrally coiled whorls ; the initial chambers are very 

 small, indistinct and almost masked by the surface rugosity ; they are followed by much 

 large, roughly globular, compressed chambers which increase slowly in size ; the last 

 whorl is composed of 4 large, roughly ovoid, slightly inflated chambers which are 

 elongated in the direction of coiling, and increase slowly in size, except for the last 

 which is much smaller than the penultimate ; on the ventral side the chambers are 4, 

 large, globular and strongly inflated ; sutures on the dorsal side slightly curved, 

 depressed ; on the ventral side they are straight, radial and strongly incised ; umbili- 

 cus small, deep and open ; aperture a low, interiomarginal, extraumbilical-umbilical 

 slit ; wall calcareous, perforate ; surface heavily nodose with the nodes tapering out 

 in the form of thick, stout, spine-like projections especially on the ventral side and 

 along the periphery. 



Dimensions of described specimen. 



Maximum diameter = 0-43 mm. 



Minimum diameter = 0-33 mm. 



Thickness = 0-28 mm. 



Remarks. Berggren (1960a) removed this species to the genus Globigerina, but 

 the forms figured by him are different from the type specimens of Loeblich & Tappan 

 (1957a). 



Globorotalia irrorata is distinguished from GlobigerinasoldadoensisBr6nmma.rmbyits 

 larger size, more globular chambers, more rounded and lobate periphery, and extraum- 

 bilical aperture. It differs from A carinina intermedia Subbotina in its quadrate outline, 

 chambers which increase slowly in size, and much smaller last chamber. Acarinina 

 clara Khalilov (1956) is closely related to the present species, but has a higher dorsal 

 side, a greater number of chambers, more whorls and a densely porous surface with 

 short spines between the pores. 



Globorotalia irrorata probably evolved from G. quadrata (White) by the 

 development of the heavily spinose surface, and into G. berggreni sp. nov. by the 

 increase in the rate of coiling and in the surface rugosity, by the slight compression of 

 test, the reduction in the size of the umbilicus, and by the development of the long 

 narrow aperture. The stratigraphical distribution of these species substantiate 

 this proposition although no direct evidence was recorded. 



Hypotype. P.45612. 



Horizon and locality. Figured specimen, from sample No. 51, Gebel Owaina 

 section. 



Stratigraphical range. The species was described by Loeblich & Tappan 

 (1957a) from the Coal Bluff marl member of the Naheola formation, and from the 

 Nanafalia formation of Alabama which they considered as Upper Thanetian and 

 Lower Eocene respectively, although the latter is most probably of Upper Paleocene 

 age as well. 



In the Esna-Idfu region G. irrorata is a rare to common form in the G. aequajG. 

 esnaensis Subzone of uppermost Paleocene age. 



