PLANS OF GEOWTH 45 



when the specimen is megalospheric — that is, with a 

 large central chamber — there is a boss generally 

 visible at the umbilical centres of the shell, the 

 exterior of the megalosphere ; for this is nsually left 

 uncovered by the involving series of chambers of 

 later growth. Sometimes the coiling of the shell is 

 rapid, and then there are few chambers to each 

 turn, as in Glohigerina. 



Leaving the forms which have a series of 

 chambers arranged along a single axis, we come to 

 the biserial forms, those which have two rows of 

 segments side by side, which are not connected 

 with each other on the same line of growth, but are 

 connected by stolons to the segments above and 

 below on the opposite side, as in Textuldi-ia. Other 

 forms are in a similar manner arranged in three rows 

 (triserial), as in Tritaxia. 



Another plan, the cyclical method of growth, 

 seems to be derived from the spiral, for both in 

 Orhitolites and Cycloclypjeus the earlier segments show 

 a tendency to a spiral manner of growth, but this 

 soon changes into the concentric by the segments 

 budding, not on one side only, but all round, so as ta 

 form a ring or annulus of chaniberlets. 



There are many other fundamental forms — for 

 instance where the axis has, so to speak, been 

 twisted during the growth of the shell, as in B)tU- 

 vtiiKi. Others are represented not only by the 

 apparent twisting of the axis of growth, l)ut also by a 

 folding and inrolling, which are represented by the 

 forms Cassid'uUna and EJtrenhergina. 



