34 
DE. CAEPENTEE’S EESEAECHES ON THE EOEAAIINIEEEA. 
already been made, which causes them to unite at intervals with the spii’al lamina that 
is subsequently formed over them ; so that they are marked on its external surface by the 
non-tubularity of its substance in those parts which immediately overlie them. 
169. Allowance being made for the differences arising out of this diversity in them 
plan of conformation, we find an extraordinary resemblance in the general organization 
oi AmpUstegina Cmmngii to that of the Opermlina akeady described, as will be appa- 
rent from a comparison of figs. 6, 6, Plate VI. to figs. 8, 10, Plate IV. of OpercuUna. 
Hence it will be quite unnecessary to enter into any minute description of its structure. 
In regard to the mode of communication between the chambers,— by one pilncipal 
orifice in the form of a narrow slit along the inner margin of each septum, with a 
variable number of secondary apertures irregularly disposed in difierent parts of the 
septal plane, — there is an absolute identity with Opermlina ; as there is also in the dis- 
tribution of the interseptal passages between the two layers which each septum here 
unmistakeably exhibits. The marginal cord, likewise, exhibits the same peculiarity 
of organization as in Opermlina ; being channeled out by freely inosculating passages 
which communicate with those of the interseptal system (Plate VI. fig. 6). This mar- 
ginal system of passages is even more developed than in Opermlina ; and a study of its 
distribution will, I think, remove all doubt as to the correctness of my interpretation of 
the appearances often presented by sections of the marginal cord in that genus 156). 
There is this difference, however, in the relation of the interseptal to the marginal 
system of canals in these two types,— that the interseptal canals of AmpUstegina appear 
to take their origin directly from some of the large superficial passages of the marginal 
cord on which the septum abuts, instead of branching from a pak of regular spkal canals 
as in Operculina, no distinct evidence of such canals having here presented itself to me. 
170. The relationship of AmpUstegina Cwmingii to those forms of Nummulites in 
which the alar prolongations of the chambers of each whorl are continued, mth centri- 
petal prolongations of the septa, over the whole surface of the penultimate whorl, is 
obviously extremely close; in fact, I can discern no distinguishing character between 
these two types, except that which is afforded by the tendency of the last turn of the 
spire of AmpUstegina to open out, whilst that of Nummulites closes in. The double- 
coned axis of non-tubular substance would seem to be a distinctive character of Ampln- 
stegina-, but I am not inclined to lay much stress upon it, as it presents itself in veiy 
different proportions in different individuals. 
171. Whilst the type which I have now been describing is thus closely related to the 
highest because most specialized forms of Foraminiferous organization, it is smgular 
that the smaller species to which I have referred under the name of A. gihhosa should 
present such a marked inferiority of conformation. Its spkal lamina is as minutely 
tubular as that of its congener ; but I have not been able to detect the least trace of a 
system of interseptal canals ; and it is especially to be noticed, that the marginal cord, 
which exhibits such a high development of the canal-system in A. Gumingi% consists in 
A. gihhosa of homogeneous non-tubular shell-substance, without any vestige of canals. 
