Dimorphism of the Foraminifera. 



3;J9 



pressa, d'Orb. (tig. 2), shows that the first ten chambers 

 surrounding the central chamber are arranged in five series ; 

 but suddenly the succeeding chambers become more embracing 

 and arrange themselves like those of the form A (fi 



Biloculina comata 7 Brady, form A (fi 

 inhabits the Atlantic Ocean, possesses a central chamber 

 smaller than that of B. depressa ; its walls are very thin ; it 



g- 



1). 





3), which also 



A. Fig. 3 (magn. 12). 



B. Fig. 4 (magn. 28). 





Biloculina comata. 



is nearly spheroidal, its greatest diameter being 258 /*, and its 

 smallest 240 fi. Towards its upper part we see the oval sec- 

 tion of the first chamber, which resembles a narrow canal and 

 is very different from the following ones. This character, 

 which is common to all the Biloculince. may be verified in 



The following chambers have the normal arrangement of 

 this genus (coiling in a single plane of symmetry); but their 



^ ^ ^ ft * V V V ■ ■ ■ 



riblets. 



very 



Biloculina cnmata, Brady, form B (fig. 4) *. — The central 

 chamber is spheroidal and very small (21 fi) ; the first cham- 

 bers which surround it are grouped at first by five, then by 

 four, three, and two; and it is only from this moment that the 

 chambers are arranged as in the Biloculina?. There is then 

 only a single plane of symmetry common to the last chambers, 

 the coiling taking place in a single direction. These diffe- 

 rent phases of the coiling therefore remind us, in one and the 

 same species, of the arrangement of the Qutnqueloculince, 

 Triloculifue 7 and BilocuMnce. 



In an early communication we shall indicate the modifica- 

 tions that we have ascertained in other genera, and give the 



* In our figure the last chamber but one is incomplete, and the last one 

 is entirely wanting*. 



