484 



GENERAL CHARACTERS OF FORAMIN1FERA. 



chiefly belonging to the genus Nodosarina ; but even in that genus 

 we have every gradation between the rectilineal (fig. 10), and the 

 spiral mode of growth (fig. 11); whilst in the genus Peneroplis 

 (fig. 5) it is not at all uncommon for Shells which commence in a 

 spiral to exchange this in a more advanced stage for the rectilineal. 

 When the successive segments are added in a spiral direction, the 

 character of the spire will depend in great degree upon the en- 

 largement or non- enlargement of the successively-formed chambers; 

 for sometimes it opens-out very rapidly, every whorl being consi- 

 derably broader than that which it surrounds, in consequence of 

 the great excess of the size of each segment over that of its pre- 

 decessor, as in Peneroplis ; but more commonly there is so little 

 difference between the successive segments, after the spire has 

 made two or three turns, that the breadth of each whorl scarcely 

 exceeds that of its predecessor, as is well seen in the section 

 of the Rotalia represented in Fig. 255. An intermediate con- 

 dition is presented by such a Rotalia as is shown in Fig. 248 



Fir,. 248. 



Hoi olio onto to, -with its pseudopodia extended. 



