ON THE LIFE-HISTORV OF THE FORAMINIFERA. 159 



(d.) Truncatulina lobatula (W. and J.). 



When the shells of this species are decalcified, a brown and 

 apparently chitinous element remains, which retains the size 

 and shape of the chambers. This is present in the walls of the 

 inner chambers of many species,, but is particularly well de- 

 veloped in this. 



In a single example of the Microspheric form, the micro- 

 sphere measures llxlO/i, and at least seven nuclei are 

 present. 



In twelve examples of the Megalospheric form, the mean 

 diameter of the megalosphere varies between 35-5 and \5 ijl, 

 and has an average of 28 /i. In the three cases in which the 

 protoplasmic contents are preserved (including the example 

 with the megalosphere of 15 /a diameter), a single large nucleus 

 is present. 



Eight examples from Tonga appear to belong to Brady's 

 species, T. tenuimargo. They are all of the megalospheric form, 

 the mean diameter of the megalosphere varying between 24 

 and 14-5 fi, and having an average of 20'8 fi. In five specimens 

 which contain protoplasm (including that with the megalo- 

 sphere of 14 5 /a) a single large nucleus is present. 



Thus, in Truncatulina, the diameter of the megalosphere, 

 though often considerable, may be so small as to approach that 

 of the microsphere. In these cases, if the size of the central 

 chamber were the only character on which to rely, it would be 

 doubtful to which form the specimen should be referred. It 

 appears, however, that this is indicated by the character of the 

 nuclei. In the example of the microspheric form, whose central 

 chamber measures 11 x 10 yu., at least seven nuclei are present, 

 while the specimen of the megalospheric form whose central 

 chamber is smallest (14'5 /i) ha,s a single large nucleus 

 measuring 20 x 15 /i. 



15—2 



