22 
DE. CAEPENTEE’S EESEAECHES ON THE EOEAIIINIEEEA. 
sented in Fig. IV., these secondaiy pores {V, b", b'”) present a disposition which would 
seem to indicate that they are scarcely less important for the mamtenance of the com- 
munication between the chambers, than is the principal aperture itself; and it is cunous 
to observe how exactly they repeat at b' and b” that mode of communication—between 
two segments on the inner side and one on the outer—which is so characteristic of 
Orbitolites 17) and Orbiculina. Each septum, as in Cycloclypeus and Nmnmulites, is 
composed of two layers (Plate I. fig. 3 d, d\ each being the proper waU of one of the 
chambers which it separates ; these layers are commonly in close apposition mth each 
other ; but they separate at certain spots, to give passage to the very curious system of 
inter septal canals to be presently described. ^ ^ i ^ , 
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 indiiuduals, 
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 smah 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- 
Eig. VII. 
Vertical or transverse sections of six specimens of Opermlina, exhibiting marked variations 
in the form and proportions of the convolutions. 
tion between the chamber and the interseptal passages. In this idea I am now satisded, by the enamma- 
tion of Operculim, that I was in error; and I am disposed to regard these seeondmy pores ot Nu,..,uhtes 
and OfeLlim as representing the mnltiple eommnnieations between the chambers of Penereplv, (f 12,). 
