IN THE ESNA-IDFU REGION, NILE VALLEY, EGYPT 189 



Description. (Specimen, PI. 20, figs, za-d.) Test medium-sized, planoconvex, 

 umbilico-convex, coiled in a very low trochospire ; dorsal side flat ; ventral side 

 distinctly protruding with a high umbilical shoulder and a rough, beaded umbilical 

 flange ; equatorial periphery roughly ovoid, weakly lobate, with a well-developed, 

 beaded keel ; axial periphery sharply acute ; the chambers on the dorsal side increase 

 rapidly in size ; they are about n in number, arranged in 2 sinistrally coiled 

 whorls ; the initial chambers are small, indistinct and almost masked by the surface 

 rugosity ; the last whorl is composed of 5 relatively large, roughly crescentic 

 chambers ; those on the ventral side are large, strongly angular conical and increase 

 rapidly in size ; their distal ends taper out and are crowned with a papillose 

 umbilical collar ; sutures on the dorsal side distinct, flush with the surface, oblique 

 and directed sharply backwards ; on the ventral side they are radial and strongly 

 incised ; umbilicus conical in shape, very wide at its top, narrow at the bottom, deep, 

 open and surrounded by a heavily beaded collar ; aperture interiomarginal, extra- 

 umbilical-umbilical, a long, wide arch extending to the periphery with a distinctly 

 developed apertural lip ; wall calcareous, perforate ; surface delicately papillose on 

 the dorsal side, more distinctly so on the ventral, and heavily papillose in the 

 umbilical collar and the marginal keel, with the papillae sometimes tapering out in 

 the form of spine-like projections. 



Dimensions of described specimen. 

 Maximum diameter = 0-44 mm. 

 Minimum diameter = 0-32 mm. 



Thickness = 0-25 mm. 



Remarks. The species was first described by Toulmin (1941) as a variety of 

 G. wilcoxensis Cushman & Ponton. Cushman & Bermudez (1949) considered this 

 form to belong to their subgenus Truncorotalia but retained it as a variety of G. 

 wilcoxensis. 



Grimsdale (1951), followed by Hamilton (1953) and Graham & Classen (1955) 

 realizing that Toulmin's variety is unrelated to G. wilcoxensis, but is morphologically 

 very similar to G. velascoensis (Cushman), changed its name to G. velascoensis 

 (Cushman) var. acuta Toulmin. 



Haynes (1955, 1956) described as G. velascoensis (Cushman) aff. var. acuta Toulmin, 

 a form which is actually a reworked Upper Cretaceous Globotruncana species redeposi- 

 ted in the type Thanetian. 



Dalbiez & Glintzboeckel (1955) raised Toulmin's variety to specific rank and inclu- 

 ded it in Truncorotalia, a junior synonym of Globorotalia, as mentioned above. 



Bolli (19576) and Hillebrandt (1962) considered Toulmin's form to be a junior 

 synonym of G. velascoensis (Cushman), while Loeblich & Tappan (1957a) considered 

 the two species separately. In the Esna-Idfu region, where the two forms are 

 extremely well developed, their morphological characters warrant their separation. 



Globorotalia acuta Toulmin is distinguished from G. velascoensis velascoensis 

 (Cushman) by its much smaller test, tighter coiling, chambers which increase more 

 rapidly in size and are fewer both in total number and in number in the last whorl : 



