730 
DE. W. B. CAEPENTEE AND ME. H. B. BEAD I 7 ON 
study of which it will be found more easy to understand the variations from this plan 
that present themselves (1) in the first- formed layers which immediately surround the 
nucleus, and (2) in that Z«s£-formed layer which constitutes the exterior of the fully- 
developed sphere. — Such portions are shown in transverse section, as seen by reflected 
light under a power of 25 diameters, in Plate LXXIII. figs. 3, 4 ; whilst another portion 
that combines certain features presented separately in the two preceding, is shown in trans- 
parent section, by transmitted light, under a power of 70 diameters in Plate LXXVI. fig. 1. 
In the latter of these figures, to which the attention may be most advantageously directed 
in the first instance, is seen a succession of four lamellae (fil 1 , IH 2 , l 3 l 3 , IP) of labyrinthic 
substance, separated in the middle portion of the figure by interspaces which are for the 
most part wider than the lamellae themselves, but continuous with each other on either 
side. Each lamella is bordered on its inner or centrad aspect by a continuous floor [fi\ 
fi\fi 3 ,fi 4 ) composed of adherent sand-grains; which completely closes-in the labyrinthic 
structure along that face, and cuts off its chamberlets from the contiguous internal in- 
terspace, — as is yet more distinctly seen in another transparent section which crosses the 
interspaces in the contrary direction (Plate LXXV. fig. 1), and in the opaque sections 
(Plate LXXIII. figs. 3, 4). On this floor are built up (so to speak) the partitions which 
intervene between the chamberlets ; but these are so far from being complete, that the 
cavities they surround remain in free communication with each other. There is gene- 
rally to be observed, just above the floor, a row of openings more regularly arranged than 
those seen elsewhere (as is best shown in Plate LXXIII. fig. 3) ; and the disposition of 
these seems to indicate that they are the cross sections of passages running at right angles 
to the plane of section, like the longitudinal galleries which form the communications 
between the contiguous series of chamberlets in Alveolina. (See Philosophical Transac- 
tions, 1856, Plate XXIX. fig. 8, bb , cc .) The partitions between the chamberlets, 
which are composed (like the floor) of sand-grains cemented together, have a generally 
vertical (or radial) direction ; but they show no such regularity as would enable it to be 
said that they are arranged on any definite plan. They are not covered in by any layer 
corresponding to their floor; so that the chamberlets open freely into the interspace 
above ; and as this lies on their 'peripheral aspect, they must have been similarly open to 
the surrounding medium, when the layer of which they form part constituted the ex- 
ternal surface of the sphere. — The contrast between the open or external surface of each 
layer of labyrinthic structure, and its closed or internal surface, is best displayed by con- 
centric fractures separating two contiguous layers ; as shown in Plate LXXIV. figs. 1 
and 2, 3 and 4, of which a detailed description will be found in the next paragraph. 
14. It has been already pointed out, in the account of the general structure of Par- 
keria (§11 and Plate LXXII.), that the interspaces between the successive lamellae are 
traversed by radial processes composed of labyrinthic structure resembling that of the 
lamellae themselves; which bring the ‘labyrinthic systems’ of several successive lamellae 
into continuity with each other, as is shown at rp, rp, J J p’, r'p', in the highly magnified 
section represented in Plate LXXVI. fig. 1 . It is only by concentric fractures, however, 
