18 



PROTOZOA. FORAMINIFERA 



of which the wall of a new chamber is formed either by the 

 secretion of material or by cementing of foreign particles. 

 The arrangement of the chambers in the multilocular 

 Foraminifera is very varied; they may be placed in a 

 straight line as in Nodosaria (fig. 3, H), in a curved line as 

 in Dentalina, in a plane spiral as in Cristellaria (fig. 3, 67), 

 or in a helicoid spiral as in Rotalia (fig. 3, L, M). The 

 earlier whorls in some spiral forms are partly or entirely 

 covered by the later ones, so that sometimes the last whorl 

 only is visible on the exterior {e.g. Cristellaria) ; but when 

 the later chambers are merely attached to the extremities 



"0 





Fig. 1. A, section of a foraminifer in which each septum is formed of a 

 single lamella. B, in which the septum is formed of two lamellas. 

 a, passages between the chambers ; b, septum ; c, anterior wall of 

 last chamber ; d, supplemental skeleton. (After Carpenter.) 



of the earlier ones, all the whorls can be seen (e.g. 

 Operculina). Some genera, such as Textularia (fig. 3, E), 

 have two rows of chambers placed side by side ; others 

 (Tritaxia) have three. In some cases (e.g. Orbitolites) there 

 are numerous chambers arranged in concentric rings instead 

 of in a spiral. 



In the porcellanous and the simpler vitreous Forami- 

 nifera each septum (fig. 1, A, b) consists of a single lamella 



