234 upper cretaceous-lower tertiary foraminifera 



Main variation. 



i. Chambers 10-12, arranged in 2-3 whorls, generally dextrally coiled, but 



sinistral forms also occur (of 108 specimens picked at random, 36 coiled 



sinistrally). 

 2. Chambers in the last whorl 4-5. 



Remarks. Bolli (1957&) moved this species from Globigerina to Globorotalia 

 because of its interiomarginal, extraumbilical-umbilical aperture. 



The species is distinguished by its quadrate appearance, generally small last 

 chamber, radially depressed sutures, and by the rough surface of its early chambers. 



Globorotalia quadrata (White) has quite often been confused with Globigerina 

 bulloides d'Orbigny and with superficially similar Maestrichtian Rugoglobigerina and 

 Hedbergella species (e.g. White 1928 ; Nakkady 1959). G. quadrata is somewhat 

 similar to G. pseudobulloides (Plummer) from which it is distinguished by the quad- 

 rilateral arrangement of its chambers, its small last chamber, its centrally depressed 

 dorsal side, the rough surface of its early chambers and its straight, radial depressed 

 sutures on the dorsal side. Some of the forms described by Loeblich & Tappan 

 (1957a, pi. 44, figs. 4, 5) as G. pseudobulloides (Plummer), are probably G. quadrata 

 (White). 



Globorotalia quadrata (White) is believed to have evolved from G. pseudobulloides 

 (Plummer) into G. irrorata Loeblich & Tappan as suggested by their morphological 

 features and stratigraphical distribution. However, it is not excluded that the 

 present species has also evolved into G. angulata angidata (White) by flattening of 

 the dorsal side and the development of the rough surface. 



Hypotype. P. 45627. 



Horizon and locality. Figured specimen, from sample No. 7 Gebel El- 

 Kilabiya section. 



Stratigraphical range. White (1928) in his original description of the species 

 stated that it is rare in the middle and upper Mendez formation of Mexico becoming 

 quite abundant at the very base of the Velasco and onty slightly less so throughout 

 the lower part of the Velasco. It is quite evident that he confused Globorotalia 

 quadrata with similar quadrilateral Rugoglobigerina and/or Hedbergella species 

 in the Maestrichtian rocks below. Nakkady (1959) apparently made the same 

 mistake and thus recorded his Globigerina quadrata White as ranging throughout the 

 Maestrichtian-Danian-Montian of the Kharga Oasis, Egypt. His Montian is now 

 regarded as Lower Eocene. 



Bolli (19576) recorded Globorotalia quadrata (White) from the lower Lizard Springs 

 formation of Trinidad, where it was found to range through the G. uncinata Zone to 

 the G. pseudomenardii Zone. 



In the Esna-Idfu region, G. quadrata (White) floods the Upper Danian part of the 

 sections studied. It continues as an abundant to common form upwards in the 

 section, fading out gradually towards the basal part of the Upper Paleocene 

 G. velascoensis Zone where it dies out completely. 



