AKT. 6 'fORAMINIFERA: POLYMORPHINIDAE — CUSHMAN AND OZAWA 11 



Globulina has apparently triserial chambers. However, the actual 

 arrangement is not triserial but somewhat quinqueloculine. The 

 apparent triserial series of chambers has resulted from much over- 

 lapping of the chambers as shown by the text figures. 



Pyrulina is an elongate or fusiform genus, in which the chambers 

 are typically quinqueloculine in the early stage, later becoming biserial. 

 As is already noted, it is very diflEicult to separate some Tertiary and 

 Recent species of Globulina and Pyrulina from some Jurassic globu- 

 lar or fusiform species because of their homeomorphy or parallel 

 evolution. 



Pyrulina and Globulina are abundant in the Upper Cretaceous, 

 Eocene, Oligocene, and Miocene. In the Pliocene and Recent, they 

 are of rather rare occurrence compared with other genera. 



Glandulina, as far as its genotype species Glandulina laevigata is 

 concerned, is closely related to Pyrulina and should be included in the 

 Polymorphinidae. The microspheric form of Glandulina laevigata has 

 the early chambers invariably arranged in a biserial series, although 

 in the later stage and also in the megalospheric form the septa are 

 almost horizontal and parallel. 



In the Upper Cretaceous Pseudopolymorphina is introduced. It 

 has a test with the early chambers arranged in a quinqueloculine 

 series, while the later ones become biserial and the chambers are 

 slightly overlapping. 



Much more advanced genera such as Sigmomorphina, Sigmoidella, 

 and Polymorphina appear for the first time with the beginning of the 

 Tertiary. Sigmoidina is a group having a quinqueloculine arrange- 

 ment of chambers as in Guttulina, but each succeeding chamber 

 extends down to the base and embraces the earlier ones, so that but 

 a few chambers are visible from the exterior. 



Sigmoidella is undoubtedly related to Sigmoidina, and the chambers 

 are involute, but they are arranged in an open sigmoid series. 



Sigmomorphina arose from Guttulina s. str. by developing elongated 

 chambers added laterally in a sigmoid series. In some elongated 

 Sigmomorphina each succeeding chamber in the later stage is removed 

 much farther from the base. Sigmomorpha, the genotype species of 

 which is S. sadoensis, is included in Guttulina, after the detailed exam- 

 ination of numerous species, although some specimens show a more 

 or less sigmoid arrangement of chambers. 



Polymorphina is the most advanced and specialized genus. The 

 primitive forms have a sigmoid arrangement of chambers in their 

 early stages, but the advanced species are entirely biserial, and each 

 succeeding chamber is farther removed from the base. 



Dimorphina tuberosa seems to us to be a very doubtful species. 

 Ozawa found that the original specimen has been lost, and the figures 



