IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 135 



Lapparent) as he found them together at the same stratigraphical level and they 

 looked the same in thin sections. 



Dalbiez (1955 : 163-164) included G. stuarti (de Lapparent) with G. elevata 

 (Brotzen) and G. rosetta (Carsey) in one group, depending on the fact that they are all 

 umbilico-convex and entirely single keeled. However, G. rosetta (Carsey) proved to 

 have two closely-spaced keels on the early chambers of the last whorl, joining to 

 form a single keel on the last two chambers. On the other hand, G. elevata has a 

 distinctly lobate periphery and typically petalliform chambers as opposed to the 

 entire non-lobate periphery and trapezoidal chambers of G. stuarti. With this in 

 mind, Dalbiez (1955 : 169) described G. elevata stuartiformis as a new subspecies. 

 However, this form is actually more closely related to G. stuarti, hence Pessagno 

 (i960) quite justifiably, changed its name to G. stuarti stuartiformis Dalbiez. On 

 the other hand, Pessagno (i960 : 101 ; 1962 : 362) considered G. elevata (Brotzen) to 

 be a subspecies of G. stuarti and changed its name to G. stuarti elevata (Brotzen). 

 However, the morphological characteristics and stratigraphical ranges of these 

 two species strongly favour treating them as two distinct species. 



Dalbiez (1955 : 164) suggested that G. stuarti stuarti (de Lapparent) had evolved 

 from G. stuarti stuartiformis Dalbiez during Upper Campanian time by the develop- 

 ment of a biconvex test and by the change of the triangular chambers on the dorsal 

 side into the characteristic trapezoidal form. He also added that the whole group 

 elevata-rosetta-stuarti had probably originated from G. sigali Reichel of the 

 Lower Turonian, although he had no direct evidence. However, it now seems 

 more logical to suggest that G. stuarti stuarti evolved from G. stuarti subspinosa in 

 Upper Campanian-Early Maestrichtian time by the development of a more regular 

 test, with a circular, entire periphery and narrow chambers which are strongly 

 elongated in the direction of coiling. On the other hand, G. stuarti stuarti is believed 

 to have evolved into G. stuarti parva during Lower-Middle Maestrichtian time by the 

 development of a smaller test with fewer chambers in the last whorl, which increase 

 more rapidly in size. These suggestions conform well with the morphological 

 development and stratigraphical ranges of these subspecies, and are substantiated by 

 a whole series of transitional stages between them (see PL 9, figs, za-d ; PL 10, figs. 

 la-d). 



Nakkady (1951a, pi. 1, fig. 4A) included in Globotruncana area, typical G. stuarti 

 stuarti (de Lapparent), as examination of his specimens (B.M.N.H., P. 41779) has 

 revealed. 



Bolli (1951) described as G. stuarti (de Lapparent) a form which is typical of 

 G. stuarti parva Gandolfi, while Papp & Kiipper (1953) described as G. stuarti a form 

 which most probably belongs to G. elevata (Brotzen). 



Gandolfi (1955) described as G. stuarti stuarti (de Lapparent) a form which appears 

 to be transitional between G. stuarti subspinosa Pessagno and typical G. stuarti stuarti. 

 Such forms were also recorded from the Esna-Idfu region, e.g. PL 10, figs. la-d. 

 Gandolfi also considered G. conica White as a subspecies of G. stuarti (de Lapparent) 

 and changed its name to G. stuarti conica (White). However, Gandolfi's form is 



