IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 137 



1955 Globotruncana (Globotruncana) elevata stuartiformis Dalbiez : 169, text-figs. loa-c. 



1956 Globotruncana elevata stuartiformis Dalbiez ; Knipscheer (pars) : 52, pi. 4, figs. 4a, b, 

 ? 12a— c ; non figs, ga-iob, i^a-i^b. 



i960 Globotruncana (Globotruncana) stuarti stuartiformis Dalbiez ; Pessagno : ior, pi. 5, 



figs. 7, 11. 

 ? i960 Globotruncana stuarti (de Lapparent) ; Vinogradov, 315, pi. 6, figs. 2ga-^oc. 

 1962 Globotruncana (Globotruncana) stuarti stuartiformis Dalbiez ; Pessagno : 362, pi. 2, 



figs. 4-6. 



Emended diagnosis. A single keeled Globotruncana with last-formed chambers 

 triangular in shape, moderately lobate periphery, typically straight, raised sutures 

 tangential to preceding whorl on dorsal side, roughly wedge-shaped appearance in 

 side view ; typical stuarti-form chambers on ventral side, and relatively small 

 umbilicus surrounded by raised, thick, beaded ridges. 



Description. Test medium-sized, almost planoconvex, coiled in a very low 

 trochospire ; dorsal side very slightly convex to nearly flat, gently sloping towards 

 the periphery ; ventral side strongly protruding especially in the later part as the 

 convexity of the ventral side increases gradually towards the last chamber ; equatori- 

 al periphery nearly ovoid, moderately lobate ; axial periphery acute, with a single, 

 well-developed, beaded keel ; chambers on the dorsal side 15, arranged in 2,\ dextrally 

 coiled whorls ; the initial chambers are small, slightly inflated, globigerine, and are 

 followed by crescentic chambers towards the end of the second whorl ; the last whorl 

 is composed of 5 large chambers, the first two of which are nearly crescentic, while 

 the last three are typically triangular ; on the ventral side the chambers are 5, 

 large, stuarti-form with the sutures more strongly curved forward, thus becoming 

 nearly ovoid, strongly overlapping, distinctly outlined and strongly inflated, with 

 the surface somewhat steeply sloping towards the periphery, especially in the last 

 chambers ; sutures on the dorsal side slightly curved in the early part, nearly 

 straight and tangential to the preceding whorl in the last part, limbate, raised and 

 beaded, with the beading fading out gradually towards the last whorl ; on the 

 ventral side the sutures are strongly curved forward, limbate, raised and faintly 

 beaded ; umbilicus relatively small, roughly hexagonal in outline, moderately deep, 

 surrounded by much thickened, strongly raised, faintly beaded ridges, and covered 

 by complex tegilla of which remnants are still preserved ; primary apertures interio- 

 marginal, umbilical ; tegilla with accessory apertures only poorly preserved ; wall 

 calcareous, perforate, except for the imperforate keel and tegilla ; surface smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-51 mm. 

 Minimum diameter = 0-39 mm. 



Thickness = 0-26 mm. 



Variation. Dalbiez in his original description of G. stuarti stuartiformis mention- 

 ed a wide range of variation for this subspecies. In the Esna-Idfu region, as we 

 have only the uppermost stages of development of this subspecies, the range of 

 variation is much more limited, and is as follows : 



