238 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



In the Esna-Idfu region, G. trinidadensis floods the Danian in the sections studied 

 and continues in the lower part of the Middle Paleocene G. angulata Zone where it 

 dies out completely. 



Globorotalia troelseni Loeblich & Tappan 

 (PI. 17, figs, xoa-c) 

 1957a Globorotalia troelseni Loeblich & Tappan : 196, pi. 60, figs. i,a-c ; pi. 63, figs. 5<z-c. 



Description. Test medium sized, weakly biconvex, compressed, coiled in a very 

 low trochospire ; dorsal side weakly inflated, with the initial chambers slightly 

 depressed ; ventral side slightly inflated with a depressed umbilicus at its centre 

 within which a portion of the earlier whorl is visible ; equatorial periphery roughly 

 ovoid, distinctly elongate, and moderately lobate ; axial periphery subacute with a 

 weakly develpoed marginal keel on the last chamber ; chambers on the dorsal side 11, 

 arranged in 2 dextrally coiled whorls ; the initial ones are small, very weakly inflated, 

 roughly globigerine and slightly depressed ; the last whorl is composed of 6| chambers 

 which are slightly compressed, globular in the early part, roughly lenticular, irregular, 

 compressed later, and which increase so rapidly in size that the last chamber consti- 

 tutes more than one third of the test ; on the ventral side, 8 chambers are visible ; 

 they are globular, slightly compressed in the early part, roughly lenticular, compres- 

 sed later and increase rapidly in size ; the extra if are seen within the umbilical 

 depression due to the tendency towards evolute coiling in the last whorl ; sutures on 

 the dorsal side slightly curved, depressed ; on the ventral side they are very gently 

 curved to almost straight, radial and depressed ; umbilicus very small, shallow ; 

 aperture interiomarginal, extraumbilical-umbilical, a narrow arch extending to the 

 periphery, with a small, delicate lip ; wall calcareous, perforate ; surface smooth 

 with few, small, scattered papillae. 



Dimensions of described specimen. 

 Maximum diameter = 0-33 mm. 

 Minimum diameter = 0-20 mm. 



Thickness = 0-12 mm. 



Remarks. Loeblich & Tappan (1957a) stated that " This species is characterized 

 by its tendency to become evolute, so that the early whorls are visible from both the 

 spiral and umbilical sides." However, it is only the last 2 or 3 chambers of the 

 early whorl that are visible within the umbilicus, not the whole of the whorl, other- 

 wise it would not be considered a true Globorotalia. 



Because of this tendency towards evolute coiling in the last whorl, G. troelseni 

 may be considered as a link between Globorotalia and Globanomalina ; forms such 

 as Globanomalina eocenica (Berggren) might possibly have evolved from G. troelseni 

 in Lower Eocene time. On the other hand, G. troelseni is believed to have evolved 

 from G. emilei sp. nov. in Upper Paleocene time by the development of a weak keel 

 and the tendency towards evolute coiling in the last whorl. 



The form figured as G. troelseni by Berggren (1960c) does not show the tendency 

 towards evolute coiling which is the main characteristic of this species. It may 



