26 



DE. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



with the plexus within by inosculating branches, whose apertures may sometimes be 

 detected in the bottom of the furrows. This furrowed surface of the marginal band, 

 and the existence upon it of apertures communicating with a set of canals in its sub- 

 stance, were specially pointed out by me in Nummulites (loc. cit.), although the changes 

 produced by fossilization prevent the full extent of the " marginal plexus " from being 

 traced out in that genus. The general relation of the marginal cord (a a) to the two 

 spiral laminae (b, b) with which it unites itself to form the boundary of the chambers, as 

 seen in Plate IV. figs. 15, 16, is precisely the same in Operculina as in Nummulites. 



157. The " marginal plexus" of canals communicates freely with the system of " inter- 

 septal canals," which are disposed between the two layers of the septa, as I have 

 described in Nummulites and in Cycloclypeus, and the existence of which in Operculina 

 has been already indicated by Mr. CARTER. The distribution of these is well seen, not 

 only in vertical sections which have happened to traverse the septa, as in Figs. V., VII., 

 and in Plate IV. fig. 8, but also in specimens laid open by fracture in the same direc- 

 tion, especially after the canals have been more distinctly marked out by the imbibition 

 of a colouring liquid (Fig. VIII., and fig. 2, Plate V.). It will be seen from these 

 delineations, all of which are faithfully copied from specimens in my possession, that 

 the distribution of the interseptal canals, whilst presenting a certain general uniformity 

 of plan, is by no means constant in detail. In Figs. VII. A, and VIII. D, we see two 

 principal trunks passing from the two angles of the fissure at the interior edge of each 

 septum, towards the marginal band at its exterior (as in fig. 2 d, Plate VI.), and sending 

 out branches which ramify over the part of the septum that joins the spiral lamina 

 (Fig. VIII. D), leaving the intervening portion untraversed ; and this is the only arrange- 

 ment which has been described by Mr. CARTER. But on looking at the other figures, it 



Tig. VIII. 



Septal planes of four specimens of Operculina, showing varieties in the 

 disposition of the interseptal canals. 



