IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 175 



Globigerina spiralis Bolli 

 (PL 16, figs. 2a-c) 



19576 Globigerina spiralis Bolli : 70, pi. 16, figs. 16-18. 



19606 Globigerina spiralis Bolli ; Bolli & Cita : 12, pi. 32, figs. 2a-c. 



1962 Globigerina spiralis Bolli : Hillebrandt : 122, pi. 11, figs, zoa-b. 



Description. Test medium sized, coiled in a relatively high trochospire ; dorsal 

 side highly convex ; ventral side moderately inflated ; equatorial periphery roughly 

 ovoid, lobate ; axial periphery rounded ; chambers on the dorsal side 22 in number, 

 increasing regularly in size and arranged in 4 dextrally coiled whorls ; initial chambers 

 small, inflated, globigerine, slightly compressed, increasing moderately in size and 

 followed by slightly less globular chambers which are moderately elongated in the 

 direction of coiling and increase slowly in size ; the last whorl is composed of 4^ 

 relatively large, crescentic to roughly quadrate chambers which are strongly elongated 

 in the direction of coiling and increase slowly in size ; the 4J chambers on the 

 ventral side are relatively large, roughly globular, and increase slowly in size ; 

 sutures on the dorsal side short, almost straight, radial and depressed ; on the 

 ventral side they are long, straight, radial and strongly incised ; umbilicus narrow, 

 open, filled with foreign material ; aperture interiomarginal, umbilical, partially 

 covered with the foreign material filling the umbilicus ; wall calcareous, perforate ; 

 surface smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-34 mm. 

 Minimum diameter = 0-29 mm. 



Thickness = 0-26 mm. 



Remarks. Globigerina spiralis Bolli is distinguished by its medium to small 

 sized, smooth, highly trochospirally coiled test ; its short, almost straight, depressed 

 dorsal sutures ; and long, straight, depressed, ventral ones ; its chambers which 

 increase slowly in size ; and its narrow umbilicus. 



The species is morpholgically similar to both Globigerina edita Subbotina and 

 Globigerina compacta Hofker. An examination of the holotypes of these forms is 

 needed to establish their relationship. 



Loeblich & Tappan (1957a) and Olsson (i960) described as G. spiralis Bolli, forms 

 with a rough spinose surface. These probably belong to Globigerina aquiensis 

 Loeblich & Tappan as suggested by their morphological features and stratigraphical 

 distribution. 



G. spiralis Bolli probably evolved from G. arabica sp. nov. by a reduction in the 

 size of test and in the number of chambers in the last whorl, by the development of 

 more tightly coiled chambers which are strongly elongated in the direction of coiling, 

 a higher dorsal spire and a much narrower umbilicus. The morpholgical features 

 and stratigraphical distribution of these two species support this proposition, 

 although no direct evidence was recorded. On the other hand, G. spiralis probably 

 evolved into G. haynesi sp. nov. in the upper Danian time by a reduction in the number 



