88 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



Emended diagnosis. A Globotruncana with large, broadly conical test ; 

 almost circular slightly lobate equatorial periphery, and angular to subangular axial 

 one ; entirely single keel ; broadly conical dorsal side and flat to slightly concave 

 ventral one ; numerous chambers and whorls, and large number of chambers in 

 last whorl ; globigerine initial chambers and subcircular to crescentic intermediate 

 ones, which become roughly rectangular in last whorl ; raised, beaded, almost 

 straight dorsal sutures, and curved, depressed ventral ones ; ovoid overlapping 

 chambers on ventral side and wide deep umbilicus. 



Description. Test large, broadly conical ; dorsal side highly raised, with the 

 various whorls arranged in the form of a cone with a rather sharp apex and a very 

 broad base ; ventral side flat although the chambers are slightly inflated ; equatorial 

 periphery almost circular, slightly lobate with a single, well-developed, beaded keel ; 

 axial periphery subangular ; chambers on the dorsal side 24, arranged in 4 dextrally 

 coiled whorls ; the initial chambers are very small, slightly inflated, globigerine and 

 are followed by relatively larger chambers which are crescentic to semicircular and 

 increase moderately in size ; the last whorl is composed of 6 large, roughly rectangular 

 chambers which are elongated in the direction of coiling and increase slowly in size ; 

 on the ventral side the chambers are 6, roughly ovoid to subcircular, slightly elonga- 

 ted, moderately inflated and overlapping especially in the later part ; sutures on the 

 dorsal side slightly curved in the early part, almost straight and angular later, 

 distinctly raised, thickened and beaded ; on the ventral side the sutures are depressed, 

 generally curved forward in the later part, tending to be nearly radial in the early 

 part, beaded and running in sutural depressions formed by the slight inflation of the 

 chambers ; umbilicus circular, relatively wide, deep, surrounded by slightly raised, 

 beaded ridges 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 smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-51 mm. 

 Minimum diameter = 0-48 mm. 



Thickness = 0-28 mm. 



Main variation. 



1. Chambers 21-24, arranged in 3-4 whorls generally dextrally coiled (all 



studied specimens coiled dextrally). 



2. Chambers in the last whorl 6-7, rarely 8. 



Remarks. Globotruncana conica was first described by White (1928), but his 

 description was so short and incomplete that the species has often been misidentified, 

 and its morphological characters and stratigraphical range much confused. The 

 short description led most of the following authors to describe any Globotruncana 

 species with a convex dorsal side and a flat ventral one as G. conica White. As a 

 result, most of the existing figures are inadequate and most authors tend to speak of 

 G. cf. conica White, rather than G. conica White. 



