232 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



as a rare to common form in the overlying G. pseudomenardii Subzone, and dies out 

 in the basal part of the Upper Paleocene G. aequajG. esnaensis Subzone. 



Globorotalia pusilla pusilla Bolli 

 (PI. 17, figs. Ilfl-c) 



1957b Globorotalia pusilla pusilla Bolli : 78, pi. 20, figs. 8-10. 



1960& Globorotalia pusilla pusilla Bolli ; Bolli & Cita : 28-29, pi. 32, figs. a,a-c. 



1962 Globorotalia (Globorotalia ?) pusilla pusilla Bolli ; Hillebrandt : 128, pi. 11, figs. 18a, b. 



Description. Test small, biconvex, coiled in a low trochospire ; dorsal side 

 moderately convex, inflated, slightly imbricate ; ventral side convex, inflated, 

 moderately protruding ; equatorial periphery nearly circular, moderately lobate ; 

 axial periphery subacute, without keel ; chambers on the dorsal side 17, arranged in 

 3 dextrally coiled whorls ; the initial ones are small, inflated, globigerine, and are 

 followed by typically crescentic inflated, strongly imbricating chambers which 

 increase moderately in size ; the last whorl is composed of 5, large, typically crescen- 

 tic, slightly inflated, strongly imbricating chambers which are elongated in the 

 direction of coiling ; on the ventral side the chambers are 5, large, roughly triangular 

 and moderately inflated ; sutures on the dorsal side strongly curved, depressed ; on 

 the ventral side they are almost straight, radial and depressed ; umbilicus small, 

 shallow and open ; aperture interiomarginal, extraumbilical-umbilical, a long, 

 narrow arch, with a narrow delicate lip ; wall calcareous, perforate ; surface smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-31 mm. 

 Minimum diameter = 0-26 mm. 



Thickness = 0-19 mm. 



Main variation. 



1. Chambers 12-18, arranged in 2^—3 whorls ; compressed to slightly inflated. 



2. Coiling fairly random, with a tendency to be dextral (of 126 specimens picked 



at random, 78 coiled dextrally). 



3. Chambers in the last whorl 4-6, most commonly 5. 



4. The surface is generally smooth, but a few forms with a finely hispid surface 



were also recorded and are considered to be transitional to G. convexa 

 Subbotina. 



Remarks. Globorotalia pusilla pusilla is distinguished by its small, biconvex, 

 smooth test ; crescentic, imbricate chambers on the dorsal side, and triangular, 

 inflated ones on the ventral ; its subacute axial periphery ; curved, depressed dorsal 

 sutures, and radial, strongly incised ventral ones ; its small umbilicus and narrow, 

 long aperture. 



The ancestral stock from which this species evolved is not really known. How- 

 ever, its evolution from forms such as G. uncinata uncinata Bolli or its descendant G. 

 angulata angulata (White) is possible, although no direct evidence was recorded. On 

 the other hand, G. pusilla pusilla is believed to have evolved in two directions ; one 



