236 THE FOEAMINIFEEA 



Brady, ' Geol. Mag.' 1875, p. 537, pi. xiii. figs. 6 



(7, C, 



The above species gives one a good idea of the 

 chief characters of the genus, and by referring to the 

 drawing (fig. h of Plate 13) the perfect septation will 

 be noticed, which forms its distinctive feature. It 

 occurs as a fossil in the Carboniferous limestone of 

 Eussia, China, and Sumatra. (Plate 13, figs. B, h.) 



Suh-famili/ 2. Polystomellin^. 



Test bilaterally symmetrical ; nautiloid. Lower 

 forms without supplemental skeleton or interseptal 

 canals ; higher types with canals opening at regular 

 intervals along the external septal depressions. 



Genus Nonionina^ D'Orbigny. 



Supplemental skeleton either absent or rudimen- 

 tary, and confined to the umbilical region ; no 

 external septal pores or bridges. Aperture a simple 

 curved slit. L. Cretaceous to Becent. 



Example. — N. wmbiUcatula, Montagu sp. (NaiUi- 

 liis), 'Test. Brit.' 1803, p. 191; Suppl. p. 78, pi. 

 xviii. fig. 1. 



The evenly rounded nautiloid contour of the 

 genus is well shown in the present form ; it is 

 chiefly distinguished from the other species of the 

 genus by its conspicuously sunken umbilical area. 



As a recent species N. umhilicatula is widely 

 distributed. The fossil specimens date from the 

 Middle Eocene. (Plate 13, figs. C, c.) 



