IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 243 



cus ; sutures on the dorsal side curved, raised and beaded in the early part, almost 

 straight, radial, depressed and beaded in the later part ; on the ventral side the 

 sutures are radial and strongly incised ; umbilicus large, deep, open and crowned 

 with a thick, beaded, everted collar ; aperture interiomarginal, extraumbilical- 

 umbilical ; wall calcareous, perforate ; surface smooth except for the heavily 

 beaded keel, dorsal sutures and umbilical collar. 



Dimensions of described specimen. 



Maximum diameter = o-66 mm. 



Minimum diameter = 051 mm. 



Thickness = 0-28 mm. 



Remarks. Globorotalia velascoensis caacasica was first described by Glaessner 

 (1937a) as a variety of G. aragonensis Nuttall. Glaessner included in the synonymy 

 of his new variety the form previously described by Subbotina (1936a) as Globorotalia 

 velascoensis (Cushman) var. aragonensis Nuttall which was later reconsidered by 

 Subbotina (1953) as G. velascoensis (Cushman). 



Grimsdale (1951 : 471), Subbotina (1953 : 217-218) and Berggren (19600" : 110- 

 111) considered Glaessner's variety to fall well within the range of variation of 

 G. velascoensis (Cushman). On the other hand, Reiss (1957) followed Glaessner in 

 considering this form as a variety of G. aragonensis, which he regarded as a Trunco- 

 rotalia. However, the present study showed that Glaessner's variety is more closely 

 related to G. velascoensis than to G. aragonensis, and that its morphological features 

 and stratigraphical distribution warrant its separation as a distinct subspecies. It 

 is distinguished from G. velascoensis velascoensis (Cushman) by its much larger test ; 

 wider umbilicus ; circular, distinctly lobate equatorial periphery ; much thickened, 

 heavily beaded, broader keel ; and by the roughly trapezoidal shape of its last 

 chambers on the dorsal side. 



The form figured by Hamilton (1953, p . 30, figs. 16-18) as G. velascoensis (Cush- 

 man) may belong to the present subspecies, but that figured by Sjutskaya (1956) as 

 G. aragonensis var. caacasica is different from the holotype and from the form here 

 figured. 



Globorotalia velascoensis caucasica probably evolved from G. velascoensis velasco- 

 ensis (Cushman) as it appears slightly later in the section. However, the evolution- 

 ary history of this subspecies could not be easily followed because of its rare occur- 

 rence in the samples studied. 



Hypotype. P. 45638. 



Horizon and locality. Figured specimen, from sample No. 41, Gebel Owaina 

 section. 



Stratigraphical range. G. velascoensis caucasica was recorded by Glaessner 

 (1937a) from what he described as the Lower Eocene of northwestern Caucasus. 

 It was also recorded by Sjutskaya (1956) as occurring in what she described as Middle 

 Eocene (Lutetian) of the central Sub-Caucasus, although her figures are different 

 from those of Glaessner. However, analysis of recent Soviet work by Berggren 

 (19600') led him to conclude that "... the strata in which they occur cannot be 



