REPOET ON THE FORAMINIFERA. 
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pletely enclosing those previously formed. Walls thick, finely arenaceous, cancellated ; 
sometimes developed to such an extent as to obliterate the early chamber-cavities and to 
lessen materially the size of the later ones ; smooth externally. Aperture a curved 
fissure, sometimes supplemented by a number of pores on the face of the terminal 
chamber. 
The genus Cyclammina represents the highest development of the arenaceous type of 
structure amongst living Foraminifera. Its characteristic feature, that in which it differs 
from all other recent nautiloid forms, is the peculiar labyrinthic condition of the skeleton. 
This may be best studied in the typical Cyclammina cancellata, not only on account of 
the larger dimensions of the specimens and their comparative abundance, but also because 
in that species the cancellated structure attains its fullest proportions. 
The genus has a wide geographical distribution, affecting depths of from 100 to 2900 
fathoms. It is not known in the fossil state. 
Cyclammina cancellata, H. B. Brady (PL XXXVII. figs. 8-1 G). 
“Nautiloid Lituola,” Carpenter, 1875, The Microscope, 5th ed., p. 536, tig. 274, a.b.c. 
Cyclammina cancellata (Brady, MS.), Norman, 1876, Proc. Roy. Soc., vol. xxv p. 214. 
Lituola canariensis, Carter, 1877, Ann. and Mag. Nat. Hist., ser. 4, vol. xix. p. 203, pi. xiii. 
figs. 26-29. 
Cyclammina cancellata, Brady, 1879, Quart. Journ. Micr. Sci., vol. xix., N. S., p. 62. 
„ „ Carpenter, 1881, The Microscope, 6th ed., p. 564, fig. 322, a.b.c. 
Test nautiloid, biconvex, depressed at the umbilici ; margin even or slightly lobulatecl ; 
peripheral edge rounded or subangular : composed of from two to three convolutions, the 
latest of which almost or completely encloses that preceding it. Segments numerous, ten 
to sixteen in the last convolution ; narrow, marked externally by sinuate, slightly excavated 
lines radiating from the umbilici. Chambers labyrinthic ; the cavities almost or sometimes 
entirely occupied by the extraordinary development of the cancellated finely arenaceous 
walls. Exterior surface smooth and imperforate, except where abraded ; colour, various 
shades of brown. Aperture, a crescentiform fissure, situated at the edge of the final seg- 
ment, close to its union with the previous convolution ; often supplemented by a number 
of large pores irregularly disposed on the face of the terminal chamber. Size variable ; 
diameter sometimes as much as ^th inch (6 ‘3 mm.). 
The typical Cyclammina cancellata is a large, compressed, nautiloid Foraminifer, with 
round peripheral edge ; of brown colour and smooth exterior. The entire test is arenaceous, 
and it is conspicuous amongst allied recent forms by its relatively fine dimensions. As a 
rule the test is completely involute, but in some exceptionally large specimens (fig. 8) the 
final convolution leaves the penultimate partially exposed near the centre. In the normal 
