26 
DE. CAEPENTEE’S EESEAECHES ON THE EOEAMINIEEEA. 
with the plexus within by inosculating branches, whose apertures may sometimes be 
detected in the bottom of the furrows. This furrowed surface of the margmal band, 
and the existence upon it of apertures communicating with a set of canals m its sub- 
stance, were specially pointed out by me in Nummulites {loc. cit.\ although the chanps 
produced by fossilization prevent the full extent of the “marginal plexus” from being 
traced out in that genus. The general relation of the margmal cord {a a) to the two 
spiral laminee (5, h) with which it unites itself to form the boundary of the chambers, as 
seen in Plate IV. tigs. 15, 16, is precisely the same in Ojperculina 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 Gycloclypeus, and the existence of which m Operculina 
has been afready indicated by Mr. Caetee. The distribution of these is well 
onlyin vertical sections which have happened to traverse the septa, as in Figs. V., Vii., 
and in Plate IV. tig. 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. VIIL, and tig. 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 unifoiarnty 
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 spu-al lamma 
(Fig. VIII. d), leaving the intervening portion untraversed ; and this is the only arrange- 
ment which has been described by Mr. Caetee. But on looking at the other figm-es, it 
Eig. VIII. 
Septal planes of four specimens of Operculim, showing varieties in the 
disposition of the interseptal canals. 
