46 THE GENUS POLYSTOMELLA. PART in. 



spiral, and increasing in size from the centre to the 

 last turn of the spire, which embraces and conceals all 

 that precede it. Every segment of the animal is en- 

 closed in a shell of its own, so that they are separated 

 from one another by a double wall and space between ; 

 however, they are connected in the spiral direction by 

 narrow passages in the walls. 



The segments of the animal in the exterior whorl have 

 direct communication with the water by means of a 

 shelly marginal cord, a, fig. 101, perforated by multitudes 

 of minute tubes, less than the T o~J-o-o f an 



Fig. 102. Interior of the Operculina. 



diameter, through which threads of sarcode finer than 

 those of a spider's web can be protruded. These tubuli 

 are so very fine and numerous, that they characterize 

 the Nummuline family. 



Fig. 102 represents the interior of the Operculina, 

 which is an existing representation of the Nummuline 

 type. Every segment of the animal is enclosed in a 

 shell of its own, but all the segments are connected in 

 the spiral direction by narrow passages in the walls as 

 in the Faujasina. 



Although each of the interior whorls has its perforated 

 marginal band, the segments can have no direct access 

 to the water ; however, they are indirectly brought into 

 contact with it by means of a system of branching 



