IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 241 



umbilical ; wall calcareous, perforate ; surface covered with small scattered papillae 

 in the early part, becoming smoother towards the last chamber. 



Dimensions of described specimen. 



Maximum diameter = 0-300 mm. 

 Minimum diameter = 0-200 mm. 



Thickness = o-i8o mm. 



Main variation. 



1. Chambers 12-15, arranged in 2-3 tightly coiled whorls. 



2. Coiling fairly random, with a tendency to be sinistral (of 32 specimens studied, 



20 coiled sinistrally) . 



3. Chambers in the last whorl 5-7 ; 6 is most common. 



Remarks. Globorotalia ancinata includes various forms which can be assigned 

 to the following three groups. 



(A) Forms with a small test, a flat to slightly inflated dorsal side, a subround- 



ed to subangular axial periphery, and a delicately papillose surface 

 (PL 18, figs. la-c). These are believed to have evolved from G. 

 pseudobulloides (Plummer) or its descendant G. trinidadensis Bolli, in 

 Upper Danian time. Transitional stages between these forms and 

 typical G. pseudobulloides and/or G. trinidadensis were figured by 

 Bolli (19576, pi. 17, figs 16-18) and were observed in the present 

 study. On the other hand these forms are believed to have evolved 

 into G. angulata angidata (White) in early Middle Paleocene time. 

 Transitional stages between this group and typical G. angulata 

 angidata were figured by Bolli (19576, pi. 17, figs. 10-12) and have also 

 been observed by the present author. 



(B) Forms with a relatively large test, a flat to slightly inflated dorsal side, 



a rounded to subrounded axial periphery, a distinctly nodose or even 

 spinose surface, and a thick, partially developed pseudo-keel (PL 19, 

 figs. 2a-c). These forms are believed to have evolved from group A. 

 The holotype described by Bolli (1957, pi. 17, figs. 13-15) most 

 probably belongs to this group ; it shows clearly the partially 

 developed pseudo-keel, although Bolli did not mention it in his 

 description. 



Slightly higher in the section, members of this group were found to 

 pass gradually into group C. 



(C) Forms with a medium-sized test, a flat, moderately to distinctly 



imbricate dorsal side, a strongly protruding ventral side, an acute 



axial periphery, an entire, thick, nodose keel, and a very rough, 



papillose surface. 



The first two groups, although differing in surface texture, were found to occur 



together and to have almost the same stratigraphical range. They probably 



represent the end members of one and the same species population of which Bolli's 



holotype is a central form. They are thus both grouped under G. uncinata uncinata 



