738 
DR. W. B. CARPENTER AND MR. H. B. BRADY ON 
tubes. At fi, fi is shown the solid floor, cutting off the labyrinthic structure 
of the lamella from the interspace which separates it from the previously 
formed lamella whereon it rests. — Magnified 25 diameters. 
Fig. 2. Portion of the external surface of the layer from which the layer represented in 
the preceding figure had been removed by concentric fracture : — rp, rp , radial 
processes ; l , Z, labyrinthic structure opening freely into the interspaces. — 
Magnified 25 diameters. 
Fig. 3. Portion of the internal surface of a lamella separated from that whereon it was 
deposited, by a concentric fracture passing through the apices of the conical 
radial processes, rp , rp, so as to leave them adherent to it :—fi, fi, the solid 
floor, continued over the surface of the radial processes, so as to cut off their 
labyrinthic structure from the interspaces they bound ; — t, t, orifices of the 
radial tubes laid open by the fracture. — Magnified 25 diameters. 
Fig. 4. Tangential section of a lamella, showing its labyrinthic structure, with the ori- 
fices t , t of the radial tubes cut transversely or obliquely. — Magnified 25 dia- 
meters. 
Fig. 5. Radial section of the thick outer layer (Plate LXXII. Z 4 ), showing its coarsely 
labyrinthic structure, in the midst of which are seen the orifices of radial 
tubes, t , t, and which is separated by the solid floor fi,fi, from the interspaces 
int, int beneath. — Magnified 25 diameters. 
PLATE LXXV. 
Fig. 1 . Transparent section of part of a lamella taken in a radial direction ; showing its 
labyrinthic structure cut off on its internal or centrad aspect from the inter- 
space int 1 which separates it from the previously formed lamella, by the 
interposition of the solid floor fi, fi ; while on its external or peripherad aspect 
it freely communicates with the next interspace int 2 , which is bounded peri- 
pherally by the internal of the next lamella. — Magnified 30 dia- 
meters. 
Fig. 2. Portion of the same section enlarged to 250 diameters, to show the arrangement 
of the sand-grains of which the framework is built up : — p, p, p, section of 
partitions, enclosing the chamberlets c, c ; fl,fi, part of the floor of the laby- 
rinthic structure. 
Figs. 3 and 4. Portions of thin tangential sections of lamellae of an infiltrated specimen, 
viewed as transparent objects; showing their cancelli grouped around the 
radial tubes, whose orifices are seen at t, t. The interspaces are occupied by 
crystals of calcite. — Magnified 30 diameters. 
Fig. 5. Portion of a thin transparent section of an infiltrated specimen, showing the 
appearances it presents under a magnifying-power of 15 diameters. On the 
left side the section traverses the layers tangentially, and the labyrinthic 
structure of the lamellse, the transverse sections of the radial tubes, and the 
