PLANS OF GROWTH 47 



4. Helicostega. — Body consisting of a spiral series 

 of segments. Shell made up of a number of convolu- 

 tions. The spiral may be either nautiloid (flat), as in 

 CristeUaria, or turbinoid (conical), as in Discorhina. 



5. Entomostega. — Body consisting of alternate 

 segments spirally arranged : shell chambers disposed 

 on two alternating axes forming a spiral. Example : 

 Biilini/iKi. 



(}. Enallostega. — Body composed of alternate 

 segments not forming a spiral ; chambers arranged 

 on two or three axes which do not form a spiral. 

 Examples : Tc.rfuhirid, Boliviitn. 



7. Agathistega. — Body consisting of segments 

 wound round an axis : chambers arranged in a similar 

 manner, each investing half the entire circumference. 

 Examples : Biloc/iliiia, Miliolina. 



Besides the foregoing types there is another 

 method of growth, which is provided for in Schultze's 

 classitication of the Rhizopoda, in which the segments 

 are arranged without any general plan, apparently 

 heaped together in an acervuline mass, as in Gtjp- 

 sina. 



Schultze's classification is as follows : — 



B. TESTACEA (including Foraminifera and 



ArceUlna). 



1. MONOTHALAMIA 



(=Monostega of D'Orbigny, and Arcellina). 



