i 3 4 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



circular, non-lobate, almost entire, with a single, well-developed, beaded keel which 

 slightly weakens on the last chambers ; axial periphery strongly acute ; chambers on 

 the dorsal side 21 arranged in 3! dextrally coiled whorls ; the initial chambers are 

 small, inflated, globigerine and are followed by crescentic chambers which increase 

 slowly and regularly in size as added ; the last whorl is composed of 6, narrow 

 chambers which increase slowly in size, and are strongly elongated in the direction 

 of coiling ; the first two are nearly crescentic, the last four roughly trapezoidal ; on the 

 ventral side the chambers are 6, typically quadrangular with blunt corners and 

 roughly parallel curved sides ; they are strongly overlapping, distinctly outlined and 

 strongly inflated with the sides gently sloping towards the marginal keel ; sutures on 

 the dorsal side short, slightly curved, raised and delicately beaded ; on the ventral 

 side the sutures are slightly raised and beaded, slightly curved, tending to be nearly 

 straight, except when they curve strongly around the umbilicus to form the umbilical 

 flange ; umbilicus medium sized, hexagonal in outline, relatively deep, surrounded by 

 thickened, raised, beaded ridges, and covered by complex tegilla of which remnants 

 are still preserved ; primary apertures interiomarginal, umbilical ; tegilla with acces- 

 sory apertures only poorly preserved ; wall calcareous, perforate, except for the 

 imperforate keel and tegilla ; surface smooth, with a few small papillae scattered on 

 the ventral side. 



Dimensions of described specimen. 

 Maximum diameter = 0-53 mm. 

 Minimum diameter = 0-48 mm. 



Thickness = 0-26 mm. 



Main variation. 



1. The dorsal side is very slightly raised to moderately conical, while the ventral 



side is always moderately to strongly protruding. 



2. Chambers, 18-28, arranged in 3^-4 whorls, generally dextrally coiled. 



3. Chambers in the last whorl 6-7, but 5| and 8 chambers occur as two extremes. 



Remarks. Globotruncana stuarti stuarti was first described by de Lapparent (1918) 

 as Rosalina stuarti nov. sp. Ami (1933), quite justifiably, removed this species to 

 the genus Globotruncana, although his G. ? stuarti is different from the holotype and 

 paratypes of de Lapparent. 



Recently, G. stuarti (de Lapparent) was found to include four distinct subspecies 

 which are : 



G. stuarti stuarti (de Lapparent) 1918. 

 G. stuarti parva Gandolfi 1955. 

 G. stuarti stuartiformis Dalbiez 1955. 

 G. stuarti subspinosa Pessagno i960. 

 The lumping of these subspecies and their transitional forms under G. stuarti 

 (de Lapparent), and the confusion between this species and various others, led to 

 disagreement about the diagnostic features and the stratigraphical range of G. 

 stuarti stuarti. 



Tilev (1952 : 39-41) considered G. rosetta (Carsey) to be a variety of G. stuarti (de 



