82 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



inward tilting of the dorsal surface of the last whorl the junction between the ventral 

 and dorsal sutures can be seen from the the dorsal side ; umbilicus pentagonal in out- 

 line, wide, deep, and covered by complex tegilla of which remnants are still preserved ; 

 primary apertures interiomarginal, umbilical ; tegilla with accessory apertures only 

 poorly preserved ; wall calcareous, perforate, except for the imperforate keel and 

 tegilla ; surface rough, heavily papillose or even nodose, especially in the early part 

 with the roughness decreasing gradually towards the last chamber ; the single 

 marginal keel is distinctly beaded, with the beads slightly fading out on the penulti- 

 mate and last chambers ; the keel of each chamber encircles its periphery and then 

 disappears into the short, depressed, dorsal sutures ; the umbilicus is not bordered 

 by a flange of any sort, although the large, scattered beads on the surface may 

 simulate a beaded rim. 



Dimensions of holotype. 



Maximum diameter = 0-54 mm. 



Minimum diameter = 0-42 mm. 



Maximum thickness = 0-34 mm. (Thickness of last chamber) 



Minimum thickness = 0-23 mm. (Across middle part of test) 



Main variation. 



1. Chambers on the dorsal side 13-18, most commonly 15, arranged in 2^—3 



whorls, generally dextrally coiled. 



2. Chambers in the last whorl 4^—6, slowly to moderately increasing in size. 



Remarks : Globotruncana arabica sp. nov. is distinguished by its large, concavo- 

 convex, strongly umbilico-convex, single keeled test, its large umbilicus and rough 

 surface. The only known Globotruncana species with a concavo-convex, umbilico- 

 convex test are : G. concavata (Brotzen) 1934, from the Campanian-Santonian of 

 Palestine, G. repanda Bolli 1957, from the Campanian of Trinidad, and G. bahijae 

 sp. nov. from the Maestrichtian of the Esna-Idfu region. The first species is 

 distinguished from G. arabica by its closely spaced double keel, less concave dorsal 

 side, chambers which increase more rapidly in size, and by its smooth surface. The 

 second is differentiated by its smaller test, fewer number of chambers, double keel 

 in the early part (which may be absent in the penultimate and last chambers), 

 much smaller early part, and less rugose surface. The third is distinguished by its 

 less protruding ventral side and its double keel. Globotruncana arabica sp. nov. 

 is morphologically closely related to G. repanda Bolli. Small specimens of G. arabica 

 resemble G. repanda, but differ in having an entirely single keel, and chambers 

 which increase slowly in size. By reduction of the ventral keel and increase in the 

 size of test, in the number of chambers and in the surface rugosity, G. repanda might 

 possibly have evolved into G. arabica. Such tendencies are clearly recorded in 

 G. repanda, but the latter species is known to die out completely in the Upper Cam- 

 panian, while G. arabica is only recorded from the Middle and Upper Maestrichtian. 

 Thus it is suggested that G. arabica either evolved from a yet undescribed form, 

 transitional between it and G. repanda, or that the latter also occurs in the Lower 

 Maestrichtian, but has not yet been found. 



