FAMILY GLOBIGERINIDA. 



175 



flattening out of a Rotaline spire, and the cyclical or concentric growth of chambers from its 

 margin, it takes on the form known as the Planorhulina ; and this may undergo a further 

 modification, on the one hand, by that irregular heaping up of chambers one upon another 

 which constitutes the " acervuline" mode of growtli ; on the other, by the interposition of a 

 large amount of soUd shell-substance between and upon the chambers. This acervuline 

 mode of growth is carried still further in the genus Tinoporus {Orbitolinu, D'Orb.), some forms 

 of which also present an extraordinary development of the exogenous portion of the inter- 

 mediate skeleton, strongly resembling in external aspect that of Cat carina, and accompanied, 

 like it, by a corresponding development of the peripheral part of the canal-system. And it 

 is a most interesting indication of the mutual relationship of these two types, notwithstanding 

 the complete dissimilarity of their modes of growth in their adult condition, that in their 

 early Rotaline state they are absolutely undistinguishable from each other. In Tinoporm, 

 moreover, as in CaJcarina, the setting on of the chambers follows the plan of that of the 

 lower Rotalines, not that of the higher. We are probably to rank the genus Patellina, whose 

 plan of growth tends early to become cyclical, as a still more aberrant member of the Rotaline 

 series. Finally, in PoJi/frema the growth becomes so " wild " that the aggregations of chambers 

 present a zoophytic form ; and as their origin in a Rotaline spire cannot be demonstrated with 

 certainty, their relationship to this type is established only by their conformity in structure 

 and mode of growth to the acervuline portions of Tinojiorus ; which conformity will be shown 

 to be so complete as to leave no room whatever for doubt as to their true nature. 



The following arrangement of the genera may help towards the understanding of the 

 principal relationships that have been indicated among them ; but no sucli arrangement can 

 give more than a partial view of those relationships : — 



FAMILY GLOBIGERINIDA. 

 Ovn/ttc's OrbuVum , 



Textularin^ 



BuUmina 

 Virgulina 

 Boliviua 



Cassidulina 

 Ehrenbergina 



Tcdiularia 

 Bigeueriiia 

 Gaudryina 

 Verneuilina 

 Grammostomum 



CuneoUna 



ChrysaUdlna 



GlOBIGERINvE 



Globif/erina 

 SpJieBroicUna Pullenia 



Carpenieria 



SpirilHna 



Rotaline 



Biscorbina 



Planorbtiliiia 

 Truncatulina 

 Planulin.i 

 Anomalina 



P iilvinulina 



Rofalia 



Cymbalopora 

 Calcarina 

 I'inoporu.s 

 Pat el Una 

 Polyircma 



