172 THE FOEAMINIFERA 



Siih-family 2. Buliminin^. 



Test' typically spiral, the weaker forms tending to 

 become biserial ; aperture oblique, twisted, and 

 comma-shaped. 



Genus Bulinium, D'Oebigny. 



Test spiral, elongate, more or less tapering ; often 

 triserial. Jurassic to JRecent. 



Example. — B. Presli, Eeuss, 'Verstein. buhm. 

 Kreidef.' pt. i. 1845, p. 38, pi. xiii. %. 72. 



The Cretaceous deposits furnish us with some of 

 the most characteristic species of the genus, and the 

 present one, found in the Gault and Lower Chalk, is 

 taken as a typical example. These forms are mainly 

 arenaceous in shell-structure, and for this group 

 Eeuss proposed the name AtaxojjJiragDiiuin. It is 

 difficult in practice, however, to separate the two 

 series according to the structure of the shell, as they 

 undoubtedly assume the different characters accord- 

 ing to their surroundings. Cretaceous. (Plate 9, 

 fig. N.) 



Genus VirguUna, D'Oebigny. 



Test much elongated, more or less tapering ; 

 often triserial. Lotver Cretaceous to Becent. 



Example. — V. ScJireibeisiana, Czjzek, 'Haidinger's 

 naturw. Abhandl.' vol. ii. 1847, p. 147, pi. xiii. 

 figs. 18-21. 



This species shows the tendency of this particular 

 type to assume the textularian arrangement of its 



