THE FORAMINIFERA 



103 



centre of the test) are oval, being elongated in a tangential 

 direction, and fall into lines like those on the back of a watch, 

 making what is known as the " engine turned " pattern. 





Orbitolites duplex, Carpenter, m, whole 

 test of megalospheric form, x 5 ; A A' A", 

 central parts of three varieties of the 

 megalospheric form; B, of microspheric 

 form, x 100; b, centre of latter, x 280. 



In an example of the microspheric form the microsphere is 20 /*, 

 in diameter, and here again the spiral canal is absent (Fig. 35, B 

 and b). There are eleven single chambers before the subdivision 

 into chamberlets begins, and then the orbiculine arrangement is 

 assumed, to pass in turn into the annular, as in 0. marginalis. 



In the megalospheric form the megalosphere is round or pear- 

 shaped, and has an average mean diameter of about 76 /* (the 



