IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 207 



In the Esna-Idfu region G. cf. conexa appears in the basal part of the G. velasco- 

 ensis Zone (Upper Paleocene) : it continues as a rare form throughout this zone, and 

 dies out completely at its top. 



Globorotalia ehrenbergi Bolli 

 (PL 17, figs, sa-c) 



19576 Globorotalia ehrenbergi Bolli : 77, pi. 20, figs. 18-20. 



19606 Globorotalia ehrenbergi Bolli ; Bolli & Cita : 21-22, pi. 33, figs. \a-c. 



Description. Test small, roughly lenticular, compressed, coiled in a very low 

 trochospire ; dorsal side very gently convex ; ventral side very slightly inflated ; 

 equatorial periphery roughly circular, strongly lobate ; axial periphery acute, 

 with a faintly developed keel on the last chamber (partially damaged on the figured 

 specimen) ; about 15 chambers on the dorsal side, increasing slowly in size at first but 

 more rapidly later, arranged in 2^-3 whorls ; the initial chambers are exceedingly 

 small, indistinct, globigerine and slightly inflated ; the chambers of the second whorl 

 are relatively larger, globular to roughly crescentic, and compressed ; the last whorl 

 is composed of 5, relatively large, roughly lenticular, compressed chambers, which 

 increase moderately in size ; the 5 chambers on the ventral side are roughly triangular 

 and slightly inflated ; sutures on the dorsal side are slightly curved, distinctly 

 depressed ; on the ventral side they are almost straight, radial and strongly incised ; 

 umbilicus small, shallow and open ; aperture interiomarginal, extraumbilical- 

 umbilical, a narrow long arch, covered by a delicate lip ; wall calcareous, perforate ; 

 surface smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-25 mm. 

 Minimum diameter = 0-20 mm. 



Thickness = o-io mm. 



Remarks. Globorotalia ehrenbergi is distinguished by its small, lenticular, 

 compressed, smooth test ; its curved, depressed dorsal sutures, and radial, incised 

 ventral ones ; its acute axial periphery and weakly developed partial keel ; its small 

 shallow umbilicus ; and its narrow, long aperture with its delicate apertural lip. 



This species was previously included by various authors within Globorotalia 

 membranacea (Ehrenberg), a recognized nomen nudum, under which several morpho- 

 logically and stratigraphically distinct forms had been described. In addition to 

 the known Paleocene species such as G. compressa (Plummer), G. ehrenbergi Bolli, 

 G. emilei sp. nov., G. pseudomenardii Bolli, various other forms from stratigraphically 

 distinct horizons were considered as G. membranacea (Ehrenberg). Subbotina (1953), 

 for example, included under G. membranacea (Ehrenberg), forms which are actually 

 G. compressa, G. ehrenbergi and G. pseudomenardii. 



G. ehrenbergi probably evolved from G. compressa, and is considered as an inter- 

 mediate stage between it and G. pseudomenardii. This is substantiated by their 

 morphological characters and stratigraphical ranges, although it is not excluded 



