OF THE SUB-ORDER PERFORATA. 153 



accord with each other in every point whicli concerns the characters of the individual 

 segments, and differ only as to the plan in which those segments are disposed. Now, in 

 Ampliistegina we find the spire unsymmetrical, and the general development inferior, so that 

 a certain appro.ximation is presented to the Rotalian type. In Pohjstomdla the texture of the 

 shell is far inferior in density, and the spire is much simpler ; but this type is remarkable for 

 the large amount of exogenous deposit with which the proper walls of its chambers arc 

 overlaid, and for the extraordinary development of the canal-system provided for its nutrition. 

 By the simpler or "nonionine" forms of this type, we seem carried down towards the GIo- 

 bigerine ; the connecting link being afforded by the genus PuUc/iia, which presents a strong 

 resemblance to the former, but seems essentially related to the latter. 



Such is the grouping which seems most consistent with the present state of our knowledge 

 of this important division of the Foraminifcra. That it may hereafter require modification 

 with the advance of knowledge, is by no nreans improbable ; l)ut it may be afl[irmed with 

 considerable confidence that the principles on which it is founded are correct, and that alike 

 in the affinities it indicates, and in the separations it establishes, it is a fair interpretation of 

 the most important facts which a careful study of Nature has up to this time disclosed. 



20 



