172 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIEERA 



P. 41762) confirms its identity with G. mckannai, although the paratypes (B.M.N.H., 

 P. 41763) most probably belong to a different species. 



Said & Kenawy (1956) quite unjustifiably removed Nakkady's variety to the 

 genus Rugoglobigerina and raised it to specific rank. However, these authors did not 

 give any description, and their figures alone cannot be assigned to any known form. 



Bronnimann (1952ft), Bolli (1957ft) and Hornibrook (1958) described as Globigerina 

 gravelli Bronniamnn, forms which conform well with G. mckannai White, and thus 

 G. gravelli is considered to be a junior synonym. 



Loeblich & Tappan (1957a) followed by Olsson (i960) described as Globorotalia 

 strabocella Loeblich & Tappan, a form which may probably be an extreme variant of 

 G. mckannai or a transitional stage between it and Globorotalia hispidicidaris Loe- 

 blich & Tappan. 



Globigerina mckannai White is believed to have evolved from Globigerina alan- 

 woodi sp. nov., by the development of the granular, spinose surface. On the other 

 hand, it is believed to have evolved into Globorotalia hispidicidaris Loeblich & Tappan 

 by the flattening of the dorsal side and the development of the angular truncate 

 chambers, subacute axial periphery, sharply angled umbilical shoulder and typical 

 extraumbilical-umbilical aperture. Again, it is not excluded that Globigerina 

 soldadoensis Bronnimann has also evolved from G. mckannai by the reduction in the 

 number of chambers and in the size of test. 



Globigerina mckannai White is distinguished by its large, circular, moderately 

 inflated test ; its distinctly granular, nodose, spinose surface ; slightly raised dorsal 

 side and strongly inflated ventral side ; its numerous, subglobular, inflated chambers ; 

 short, depressed, radial sutures on both sides ; and wide, deep umbilicus. 



Hypotype. P. 45580. 



Horizon and locality. Figured specimen, from sample No. 51, Gebel Owaina 

 section. 



Stratigraphical range. The species was first described from the Velasco 

 formation of Mexico which was wrongly considered by White as Upper Cretaceous. 

 Hay (i960) recorded it from the same formation, ranging throughout the Globorotalia 

 pseudomenardii and the Globorotalia velascoensis Zones which he considered as 

 Landenian. 



Reliable records show that G. mckannai White is restricted to the Upper Paleocene 

 and the basal part of the Lower Eocene. All records of this species from rocks older 

 than Upper Paleocene (e.g. Bermudez 1961 ; Nakkady 1959 ; Said & Kenawy 1956) 

 are definitely erroneous, as are records from rocks younger than the Lower Eocene 

 (e.g. Bronnimann 1952ft). 



In the Esna-Idfu region, G. mckanni White appears in the upper part of the Upper 

 Paleocene G. velascoensis Zone, the G. aequa/G. esnaensis Subzone. It floods the lower 

 and middle parts of this subzone, then fades out gradually towards the top. In the 

 overlying Lower Eocene, G. wilcoxensis Zone, a few forms were observed which only 

 differ from typical G. mckannai in having fewer chambers and being much smaller in 

 size. They probably represent the last stage in the development of this species or a 



