2 upper cretaceous-lower tertiary foraminifera 



Main variation. 



i. The test is small to large, subcircular to ovoid, moderately to strongly elongate. 



2. The dorsal side is either flat, very slightly raised or even slightly depressed, 



while the ventral side is always protruding, sometimes strongly so that the 



protruding ventral mass lies almost at right angles to the marginal periphery. 



Equatorial periphery subcircular to ovoid, slightly to moderately lobate ; 



axial periphery moderately to distinctly truncate. 

 The two marginal keels are either equally developed or the ventral keel is 



sometimes reduced on the last chamber (e.g. PL 2, fig. 26). 

 The keels, sutures and umbilical flange can either be heavily beaded through- 

 out or beaded in the early part, thickened and limbate in the later part. 

 Chambers on the dorsal side 14-16, arranged in 3 whorls, generally dextrally 



coiled (all studied specimens coiled dextrally). 

 Chambers in the last whorl 4-6, most commonly 5, large, moderately or 

 strongly elongated in the direction of coiling, increasing very rapidly in size. 

 The last chamber is either well-developed and constitutes {— I of the test 

 (e.g. PL 2, fig. 1 ; PL 3, fig. 3), or is sometimes reduced in size, becoming 

 much smaller than the penultimate (PL 2, fig. 2). 

 9. The umbilicus varies in shape, but is always wide, deep, and surrounded by a 

 raised umbilical flange which is either heavily beaded or just thickened and 

 limbate. 

 10. The surface is generally smooth but is sometimes covered by large scattered 

 papillae especially on the ventral side. 



Remarks. Globotruncana gagnebini was first described by Tilev (1951) who 

 mentioned that it morphologically resembles G. pendens Vogler, G. ventricosa White 

 and G. lugeoni Tilev, but is quite distinct. 



Bolli (195 1) and Gandolfi (1955) described as G. ventricosa White, and G. ventricosa 

 ventricosa (White) respectively, forms which are actually G. gagnebini Tilev, as in 

 part reconsidered by Bolli (1957a). Gandolfi also described as G. area caribica, 

 a form which appears to be transitional between G. gagnebini Tilev and G. aegyptiaca 

 aegyptiaca Nakkady, and is here considered to be a junior synonym of the former. 

 Gandolfi's form closely resembles the specimen here figured, PL 3, figs. la-d. 



Berggren (1962) considered G. gagnebini Tilev to be a junior synonym of G. 

 aegyptiaca aegyptiaca Nakkady, but the present study showed clearly that the 

 morphological features of the two species strongly warrant their separation in 

 spite of their apparent similarity. G. gagnebini is distinguished from G. aegyptiaca 

 aegyptiaca by its elongate, tightly coiled, ovoid test ; its greater number of chambers 

 in the last whorl which increase very rapidly in size ; its weakly lobate periphery, 

 more closely spaced keels and less rough surface. 



Globotruncana gagnebini is believed to have evolved from G. ventricosa White by 

 reduction in the size of test and in the number of chambers in the last whorl, by 

 more rapid increase in the size of the chambers, and by the development of an 

 elongate test as well as a slightly rougher surface. The morphological characters and 

 stratigraphical distribution of the two species are strongly in favour of this propo- 



