IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 131 



3. In some specimens the partly developed secondary keel is completely reduced 

 leading to forms with a single keel throughout the last whorl. 



Remarks. Globotruncana sharawnaensis is unique among the known Globotrun- 

 cana species, inasmuch as it shows a single keel on the early part of the last whorl and 

 a double keel on the last one or two chambers. The tendency to reduce the ventral 

 keel in double-keeled globotruncanas was clearly observed in various species which 

 normally show a double keel in the early part of the test and become single keeled 

 later (i.e. reduction by palingenesis). However, no species has yet been recorded as 

 having a single keel in the early stage and a double keel later, although reduction of 

 the ventral keel by proterogenesis would produce such forms. 



Forms of G. sharawnaensis, with an entirely single keel appear to be somewhat 

 similar to G. conica White. However, G. sharawnaensis is distinguished from 

 G. conica by its slightly smaller test, less conical dorsal side and slightly more 

 protruding ventral one, its somewhat rough ventral side, partially developed 

 ventral keel and acute axial periphery. It differs from G. orientalis sp. nov. in its 

 depressed ventral sutures, the character of its keels and the slightly rougher surface 

 on the ventral side. Globotruncana esnehensis Nakkady & Osman is distinguished 

 from G. sharawnaensis sp. nov. by its dome-shaped test, less protuding and more 

 undulating ventral side, more inflated chambers on the dorsal side, wider umbilicus, 

 smoother surface, and entirely single keel. 



Very little is known about the evolutionary history of G. sharawnaensis sp. nov. 

 However, it may have evolved from G. area (Cushman) into G. conica White and/or 

 G. esnehensis Nakkady & Osman, although no direct evidence was recorded. 



Holotype. P45553. 



Paratypes. P. 45554. 



Horizon and locality. Holo- and paratypes, from sample No. 20, W. 

 El-Sharawna section. 



Stratigraphical range. Globotruncana sharawnaensis sp. nov. is common in 

 the Middle Maestrichtian G. gansseri Zone of the studied sections, and dies out com- 

 pletely in the basal part of the overlying G. esnehensis Zone. 



Globotruncana stuarti parva Gandolfi 

 (PL 9, figs, za-d) 



1951 Globotruncana stuarti (de Lapparent) ; Bolli : 196, pi. 34, figs. 10-12. 



1951 Globotruncana stuarti (de Lapparent) ; Tilev (pars) ; 34-41, text-figs. 8a-d non ja-d, 



non ga-d. (See also Tilev 1952 where figures are repeated.) 

 J955 Globotruncana stuarti parva Gandolfi : 65, pi. 5, figs. ja-c. 

 1956 Globotruncana aegyptiaca Nakkady ; Said & Kenawy : 150, pi. 5, figs, iga-c. 



Description. Test small, subcircular, unequally biconvex, dorsal side very 

 slightly raised or nearly flat with a slightly raised part in the centre from which the 

 surface gently slopes radially towards the periphery ; ventral side strongly pro- 



