IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 119 



gradually upwards in the section and dies out completely in the basal part of the 

 overlying G. esnehensis Zone. 



Bolli (1957a) recognized the G. gansseri Zone in the Maestrichtian of Trinidad, 

 where he considered it to start slightly above the base of the Maestrichtian. How- 

 ever, Bronnimann & Brown (1956) considered the range of this species to be Lower 

 to Middle Maestrichtian, while the G. gansseri Zone is here considered to represent 

 the Middle Maestrichtian only. 



Globotruncana gansseri subgansseri Gandolfi 

 (PL 5, figs. 3a-d) 

 1955 Globotruncana gansseri subgansseri Gandolfi : 70, pi. 6, figs. ja-c. 



Description. Test small, subcircular in outline, almost planoconvex, umbilico- 

 convex, coiled in a low trochospire ; dorsal side flat although the early chambers are 

 slightly inflated and weakly raised above the circumambient, last whorl ; ventral side 

 strongly inflated and distinctly protruding ; equatorial periphery subcircular, 

 moderately lobate, with a single, delicately beaded marginal keel ; axial periphery 

 acute ; chambers on the dorsal side 18, arranged in 3 dextrally coiled whorls ; the 

 initial ones are very small, globigerine and weakly inflated, they increase slowly in 

 size and are followed by slightly larger, globular, inflated chambers which increase 

 moderately in size ; the last whorl is composed of 6 relatively large, crescentic 

 chambers which increase slowly in size except for the last one which is slightly 

 smaller than the penultimate ; on the ventral side the chambers are 6, subglobular, 

 strongly inflated, distinctly protruding and increase slowly in size ; sutures on the 

 dorsal side curved, slightly raised and delicately beaded ; on the ventral side they 

 are radial and strongly depressed ; umbilicus roughly hexagonal in outline, relatively 

 large, deep and covered by complex tegilla of which remnants are still preserved ; 

 primary apertures interiomarginal-umbilical ; tegilla with accessory apertures only 

 poorly preserved ; wall calcareous, perforate, except for the imperforate keel, 

 peripheral band and tegilla ; surface rough, especially on the ventral side where it is 

 coarsely papillose in the early part, with the roughness decreasing gradually towards 

 the last chamber ; the papillae sometimes taper out simulating thick spine-like 

 projections especially along the periphery. 



Dimensions of described specimen. 

 Maximum diameter = 0-35 mm. 



Minimum diameter = 0-29 mm. 



Thickness = 0-24 mm. (of last chamber) 



Remarks. Globotruncana gansseri subgansseri was first described by Gandolfi 

 (1955) who remarked that this subspecies differs from G. gansseri gansseri in having 

 a smaller test, a greater number of chambers in the last whorl, more inflated chambers, 

 and a less evident keel. 



Globotruncana gansseri subgansseri is believed to have evolved from G. gansseri 



