RHIZOPODA 11 



W. K. Taiker. The following are the primary groups of 



Foraminifcra in the system of d'Orbigny : — 



1. Monostega. — Body consisting of a single segment : shell of 



one chamber. 



2. Stichostega. — Body composed of segments disposed in a 



single line : shell consisting of a linear series of 

 chambers. 



3. Helicostega. — Body consisting of a spiral series of segments : 



shell made up of a number of convolutions. 

 4>. Entomostega. — Body consisting of alternate segments spirally 



arranged : shell chambers disposed on two alternating 



axes forming a spiral. 

 5. Enallostega. — Body composed of alternate segments not 



forming a spiral : chambers arranged on two or three 



axes which do not form a spiral, 

 (i. Agathistega. — Body consisting of segments wound round 



an axis : chambers arranged in a similar manner, each 



investing half the entire circumference. 



A somewhat different arrangement has been adopted by 

 Sehultze, who divides the Polythalamia into three sections, 

 viz. — 



1. Helieoidea, including those forms in which the several 



chambers of the shell are arranged in a convolute 

 series, and answering to the last four orders of d'Or- 

 bigny. 



2. Rhabdoidea, in which they are placed in a direct line 



(Stichostega, d'Orb.) ; and 



3. Soroidea, where they are disposed in an irregular manner 



(Accrvulina). 



Lagcna is a genus of Monostega, or single -chambered 

 Foiaminifera, with a flask-shaped shell, sometimes pre- 

 senting a beautiful fluted exterior. EntosoUnia is like a 



