22 



DE. CAEPENTEE'S EESEAECHES ON THE FOBAMINIFEEA. 



sen ted in Fig. IV., these secondary pores (#', b", b" 1 ) present a disposition which would 

 seem to indicate that they are scarcely less important for the maintenance of the com- 

 munication between the chambers, than is the principal aperture itself; and it is curious 

 to observe how exactly they repeat at V and V that mode of communication between 

 two segments on the inner side and one on the outer which is so characteristic of 

 Orbitolites (^f.17) and Orbiculina. Each septum, as in Oycloclypeus and Nummulites, is 

 composed of two layers (Plate I. fig. 3 d, d), each being the proper wall of one of the 

 chambers which it separates ; these layers are commonly in close apposition with each 

 other ; but they separate at certain spots, to give passage to the very curious system of 

 interseptal canals to be presently described. 



153. A comparison of numerous vertical sections brings into view a most remarkable 

 variety in the form and disposition of the chambers, not merely in different individuals, 

 but in different parts of the same individual. Commencing with one of the flattest 

 variety, Fig. VII. c, we observe that the breadth of the septal plane is very small in com- 

 parison with its length ; and that although the spiral lamina of each whorl except the 

 last obviously extends itself over that of the preceding whorls, the cavity of the cham- 



Fig. VII. 



K 



Vertical or transverse sections of six specimens of Operculina, exhibiting marked variations 

 in the form and proportions of the convolutions. 



tion between the chambers and the interseptal passages. In this idea I am now satisfied, by the examina- 

 tion of Operculina, that I was in error ; and I am disposed to regard these secondary pores of Nwnmulites 

 and Operculina as representing the multiple communications between the chambers of Peneroplis (^f 127). 



