204 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



lenticular and increase rapidly in size ; sutures on the dorsal side curved, depressed ; 

 on the ventral side they are very slightly curved to nearly straight, radial, depressed ; 

 umbilicus irregular in outline, narrow, shallow and open ; aperture interiomarginal, 

 extraumbilical-umbilical, a narrow, distinct arch with a delicate, flaring lip on top ; 

 wall calcareous, finely perforate ; surface smooth. 



Dimensions of described specimen. 

 Maximum diameter = 0-25 mm. 

 Minimum diameter = 0-16 mm. 



Thickness = o-io mm. 



Main variation. 



1. Chambers 12-15, arranged in 2-|~3 whorls. 



2. Chambers in the last whorl 4-5, rarely 6. 



3. Coiling is random with more tendency to dextral coiling (of 95 specimens 



chosen at random, 28 coiled sinistrally) . 



Remarks. Cushman & Todd (1942), Cushman & Bermudez (1949) and Bronni- 

 mann (1952) considered this species to belong to Globorotalia although their figured 

 forms are not true G. compressa (Plummer) 



Troelsen (1957), following Brotzen (1948), considerd this species to belong to the 

 genus Globigcrina. Dalbiez & Glintzboeckel (1955), Bolli (1957&), Loeblich & 

 Tappan (1957a, b), Olsson (i960), Bolli & Cita (1960a, b), Bermudez (1961), Berggren 

 (1962), and Hillebrandt (1962) removed this species to the genus Globorotalia. 

 Berggren (1962), following Banner & Blow's Classification (1959), considered G. 

 compressa to belong to the subgenus Turborotalia, while Hillebrandt (1962), following 

 Cushman & Bermudez (1949), considered it to belong to the subgenus Globorotalia, 

 although the latter's form is not G. compressa (Plummer). 



Hofker (i960 g : 78-79), neglecting Cushman & Bermudez (1949), Bolli, Loeblich 

 & Tappan (1957), and Banner & Blow (1959), considerd this species to belong to the 

 genus Globigerina stating that " Fine pores also are found at the somewhat compres- 

 sed periphery so that there can be no reason to call this species a Globorotalia, since 

 the type of that genus has a distinctly poreless and sharp periphery." However, 

 because of the extraumbilical-umbilical position of the aperture, this species is here 

 considered to belong to the genus Globorotalia. 



Globorotalia compressa (Plummer) is distinguished by its small, compressed, 

 biconvex test ; its strongly curved, depressed sutures on the dorsal side ; its radial, 

 depressed ventral sutures ; and its very smooth surface. 



The species is believed to have evolved from G. pseudobulloides (Plummer) during 

 the uppermost part of the Middle Danian time. On the other hand, it is believed 

 to have evolved in two directions : one leading to Globorotalia emilei sp. nov. and the 

 other to Globorotalia ehrenbergi Bolli. Globorotalia ehrenbergi is believed to be a 

 transitional stage between G. compressa (Plummer) and G. pseudomenardii Bolli, 

 although Loeblich & Tappan (1957a : 188) considered it synonymous with G. 

 compressa (Plummer). Berggren (1962 : 96), stated that " the writer has compared 

 the holotype of G. ehrenbergi (U.S.N.M.P. 5060), metatypes and topotypes of G. 



