IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 235 



Globorotalia sibaiyaensis sp. nov. 

 (PI. 23, figs. 6a-c) 



Diagnosis. A Globorotalia with small, globular, elongate test, slightly compressed 

 in early part and inflated later ; heavily spinose surface ; narrow umbilicus ; radial 

 depressed sutures and long narrow aperture. 



Description. Test very small, globular, slightly compressed, coiled in a very low 

 trochospire ; dorsal side almost flat in the early part, inflated later ; ventral side 

 moderately inflated ; equatorial periphery roughly ovoid, distinctly lobate and 

 heavily spinose ; axial periphery rounded ; chambers on the dorsal side 12, arranged 

 in two dextrally coiled whorls ; the initial chambers are small, inflated, globigerine, 

 and increase slowly in size ; the last whorl is composed of 5^ relatively large, roughly 

 globular chambers which increase gradually in size ; on the ventral side the chambers 

 are 5 \, relatively large, subglobular, slightly inflated in the early part, more strongly 

 so later ; sutures on the dorsal side very slightly curved, depressed : on the ventral 

 side they are striaght, radial and strongly incised ; umbilicus small, shallow and open 

 aperture interiomarginal, extraumbilical-umbilical, a narrow, long slit extending 

 from the umbilicus to the periphery ; wall calcareous perforate ; surface spinose and 

 nodose. 



Dimensions of holotype. 



Maximum diameter = 0-29 mm. 



Minimum diameter = 0-19 mm. 



Thickness = 0-17 mm. (of last chamber) 



Remarks. Globorotalia sibaiyaensis sp.nov. is distinguished from G. perclara 

 Loeblich & Tappan, from which it is believed to have evolved, by its smaller 

 test, entirely and heavily spinose surface, much narrower umbilicus and long slit-like 

 aperture. It is distinguished from G. uncinata uncinata Bolli by its smaller size, 

 globular form, heavily spinose surface and radial incised intercameral sutures. 

 Globorotalia intermedia (Subbotina) differs from the present species in being more 

 robust, more inflated on the ventral side and almost flattened on the dorsal, and in 

 having fewer chambers which increase rapidly in size, and are strongly protruding on 

 the ventral side, with closely adjacent umbilical ends. Globorotalia sibaiyaensis also 

 appears to be morphologically similar to the holotype of the much younger G. 

 rugosoaculeata (Subbotina) which is distinguished by its raised initial part. 



Holotype. P. 45628. 



Paratype. P. 45629. 



Horizon and locality. Holo- and paratypes, from sample No. 50, Gebel 

 Owaina section. 



Stratigraphical range. The species occurs as a rare to common form in the 

 G. aequa-G. esnaensis Subzone of uppermost Paleocene age. 



