214 THE FOEAMINIFERA 



serves to strengthen or otherwise fortify the shell, 

 called the supplemental skeleton, and these extra 

 layers and the shell-wall proper are frequently 

 traversed by a system of interseptal canals. 



In the Spirillinin.e w^e have an example of 

 perhaps the simplest type of shell, consisting as it 

 does of an open and coiled tuhe without any septa- 

 tion. In the conical modifications of this generic 

 group we seem to see the relationship between this 

 type and the genus Patellina of the next sub-family. 



In the EoTALnN.E the typical Fatellina is an 

 irregularly coiled shell forming a cone, in which the 

 spiral portion at the commencement is sometimes 

 non-septate, but this is immediately succeeded by a 

 septate, or imperfectly septate, tube. The genus 

 Cymbalopora proceeds a stage farther ; the chambers 

 are at first spirally arranged, but afterwards grow 

 in a concentric manner ; and the chambers have 

 an oblique septation somewhat similar to that seen 

 in the later whorls of Patellina. On the other 

 hand Cymbalojjora, especially the outspread modifi- 

 cations, shows some relationship with Flanorhulina. 

 The typical rotaline shells are comprised in the 

 genera Dlscorbina, Trimcatidina, Pulvinulina, and 

 Botalia ; and these, being mainly distinguished by 

 the nature of their shell-structure, present an in- 

 teresting series of isomorphous species. 



In the apparently aberrant genera Bnpertia and 

 Garpenteria the affinity to the Eotalines proper may 

 be seen in their earlier chambers, which are arranged 

 as in T rnncatulina. The sub-family of the Tino- 



