IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 237 



Description. Test large, globigerine, coiled in a low trochospire ; dorsal side 

 nearly flat in the early part, strongly inflated in the last whorl ; ventral side strongly 

 inflated ; equatorial periphery subcircular to ovoid, distinctly lobate ; axial periphery 

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

 the initial ones are very small and slightly inflated ; the last whorl is composed of 6 

 large globular, strongly inflated chambers ; on the ventral side the chambers are 6, 

 large, subglobular and strongly inflated, especially the penultimate one, which is 

 slightly shifted towards the umbilicus ; sutures on the dorsal side slightly curved and 

 depressed in the early part, nearly straight, radial, strongly depressed in the last 

 whorl ; on the ventral side the sutures are nearly straight, radial and strongly depres- 

 sed ; umbilicus irregular in outline, moderately wide, relatively deep, open ; aperture 

 interiomarginal extraumbilical-umbilical, a narrow crescentic arch with a very thin 

 lip-like flap ; wall calcareous, perforate ; surface slightly papillose in the early part, 

 becoming smoother towards the last chamber. 



Dimensions of described specimen. 

 Maximum diameter = 0-50 mm. 

 Minimum diameter = 0-36 mm. 



Thickness = 0-35 mm. 



Main variation. 



1. Chambers 14-18 arranged in 2-3 whorls generally dextrally coiled (of 175 



specimens picked at random, 67 coiled sinistrally) . 



2. Chambers on the last whorl 6-7. 



Remarks. Globorotalia trinidadensis Bolli is distinguihsed from G. pseudobidloides 

 (Plummer) by its larger size, more numerous chambers in the final whorl, slightly 

 rugose surface of the early chambers and by its last chamber which is often slightly 

 smaller than the penultimate and is slightly compressed. It is believed to have 

 evolved from G. pseudobidloides (Plummer) and to have given rise to G. uncinata 

 uncinata Bolli. This is supported by their stratigraphical ranges and by the 

 discovery in the present study of several transitional stages. 



Hyptotypes. P. 45631-32. 



Horizon and locality. Figured specimen, from sample No. 7 Gebel El-Kilabiya 

 section. 



Stratigraphical range. The species was first described from the lower part 

 of the Paleocene "Lower Lizard Springs formation of Trinidad ", where it characterizes 

 the Globorotalia trinidadensis Zone, and continues through the lower part of the 

 overlying Globorotalia uncinata Zone. Bolli (19576) did not relate his faunal zones 

 to the European divisions of the Paleocene. 



Globorotalia trinidadensis was also recorded from the Danian of the Paderno d'Adda 

 section of northern Italy (Bolli & Cita 1960a, b), from the Danian of the Tampico 

 Embayment of Mexico (Hay i960) and from the Lower Paleocene of the Gubbio 

 section, Italy (Luterbacher & Premoli Silva 1962). 



