182 UPPER CRETACEOUS-LOWER TERTIARY FORAMINIFERA 



Globigerina triloculinoides parva subsp. nov. 

 (PL 15, figs. 4«-c) 



Diagnosis. A Globigerina triloculinoides with much smaller, more tightly coiled, 

 compressed test, chambers increasing less rapidly in size and more strongly elongated 

 in direction of coiling. 



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

 with the early chambers slightly raised above the level of the last whorl ; ventral side 

 moderately inflated ; equatorial periphery roughly ovoid, moderately lobate ; axial 

 periphery subrounded ; chambers on the dorsal side are not all clear, but appear to be 

 12 in number, arranged in 2\ dextrally coiled whorls ; initial chambers are very 

 small, closely coiled, indistinct and almost masked by the surface pitting ; the last 

 whorl is composed of 3|, roughly crescentic, narrow chambers which increase moder- 

 ately in size and are strongly elongated in the direction of coiling ; on the ventral 

 side the chambers are 3|, relatively large, roughly globular, moderately inflated but 

 slightly compressed, especially the last one, and increase so rapidly in size that the 

 last chamber constitutes about half of the test ; sutures on the dorsal side, curved 

 depressed in the early part, almost straight, strongly incised later ; on the ventral 

 side they are straight, radial and strongly depressed ; umbilicus very small, narrow 

 and open, with the last chamber slightly pushed over it ; aperture interiomarginal, 

 umbilical, in the form of a long, narrow slit, with a narrow delicate flap ; wall 

 calcareous, perforate; surface densely pitted. 



Dimensions of holotype. 



Maximum diameter = 0-31 mm. 



Minimum diameter = 0-27 mm. 



Thickness = 0-25 mm. 



Remarks. Globigerina triloculinoides parva is distinguished from G. triloculin- 

 oides Plummer, from which it is believed to have evolved, by its much smaller, less 

 lobulate, tightly coiled, slightly compressed test ; its roughly crescentic, narrow 

 chambers which are elongated in the direction of coiling, and which increase less 

 rapidly in size ; by its weakly raised early whorls and slightly compressed last 

 chamber. 



Bronnimann (1952&) described as G. hornibrooki n.sp., a form which appears to be 

 closely related to the present subspecies. However, Loeblich & Tappan (1957a) 

 considered G. hornibrooki to be a junior synonym of G. triloculinoides Plummer, while 

 Bolli (19576) considered it to be a junior synonym of G. triangularis White. Indeed 

 G. triangularis White appears to be closely related to G. triloculinoides parva although 

 it is much larger, but White's description is incomplete and the form figured by Bolli 

 who had examined White's holotype, is most probably G. triloculinoides Plummer. 



Khalilov (1956) described as G. triloculinoides var. nanus, a form which only 

 differs from typical G. triloculinoides Plummer in its smaller size and slightly deepened 

 septal sutures. Khalilov's form should probably be included within G. triloculinoides 

 Plummer, and is believed to be transitional to G. triloculinoides parva. It is distin- 



