TWO GIGANTIC TYPES OF ARENACEOUS FORAMINIFERA. 
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whereby the opposed surfaces of the lamellae are separated from each other, that the form 
and arrangement of these ‘radial processes’ can be properly studied; and the appear- 
ances presented by the surfaces thus exposed are found to vary, according as the plane of 
fracture has passed through the middle of the interspace, or nearer to one of the lamellae. 
The former has been the case with the pair of lamellae of which portions of the opposed 
surfaces are shown in Plate LXXIV. figs. 1,2; the latter with the pair of which the 
outer lamella, carrying with it the £ radial processes,’ is shown in fig. 3. — In fig. 2, which 
represents the external surface of part of a lamella thus detached, we see the labyrinthic 
structure l, l , opening freely into the interspaces ; whilst these cavities are separated by 
a set of projections {rp, rp) more or less rounded in form, but connected with each other 
by bridging extensions. These are the ‘ radial processes,’ which have been broken across 
and laid open by the fracture. The converse aspect is shown in fig. 1, which represents 
the internal surface of the lamella that immediately surrounded the preceding ; for its 
deeper parts, which constitute the peripheral boundary of the interspace, are here co- 
vered by an uniform floor, fi, fl, that cuts them off from the labyrinthic substance be- 
neath ; whilst the radial processes rp, rp, which rise as elevations from this floor, are 
here less connected together, so that the interspaces form a more continuous system. 
The interior of the ‘ radial processes ’ thus laid open by transverse fracture is found to 
consist of labyrinthic structure rather coarser and less regular than that of the lamellae 
they connect ; but in each of them there is at least one large aperture, whilst not un- 
frequently there are two or even three ; and these are the cross sections of ‘ radial tubes ’ 
exactly corresponding with those which are seen in the inner layers (Plate LXXIII. 
figs. 1, 2) without any investment of labyrinthic substance. — These ‘ radial processes’ 
have not unfrequently a somewhat conical form, the apex of the cone being applied to 
the outer surface of the enclosed lamellae (with which its connexion is consequently 
slight) ; whilst its spreading base becomes continuous with the inner surface of the 
investing lamellae, into the labyrinthic system of which its own cancellated structure 
opens. Hence, when the plane of fracture passes through the apical portions of the 
cones (where the resistance to the disruption of the layers is the least), the ‘ radial pro- 
cesses ’ remain in connexion with the investing lamella, as shown at rp, rp, Plate LXXIV. 
fig. 3 ; where are also seen the continuous floor that cuts off its labyrinthic system 
from the interspace on its internal aspect, and the orifices, t, t , of the radial tubes laid 
open by the fracture. 
15. When, however, as sometimes happens, the concentric fracture passes through the 
thickness of a lamella, instead of through the interspaces and the radial processes which 
cross them, its labyrinthic system is laid open in the manner shown at Plate LXXIV. 
fig. 4 ; where we also see its chamberlets opening into the cavities of the ‘ radial tubes’ 
t, t, t, which pass into its substance. — This connexion, however, is best brought into 
view when these tubes are laid open longitudinally, either by fracture or by section ; as 
in the fractured surface shown in Plate LXXIII. fig. 4 ; where we see that the cavity of 
the tube t is formed (so to speak) by the coalescence of passages from the labyrinthic 
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