REPORT ON THE FORAM1N1FERA. 
217 
composed of a double tier of cliamberlets, one above, the other below, and the free inter- 
communication of the sub-segments of each annular chamber is still maintained by 9. 
single annular gallery ; but there are two series of radial passages (instead of one) given 
off from it, which lead respectively to the upper and lower 
tier of chamberlets of the succeeding annulus. The double 
row of marginal pores, already alluded to as visible on the 
outermost segment, are the openings of these radial passages. 
This arrangement of the parts will be readily understood by 
reference to the annexed diagram of the transverse section 
of the shell. (Woodcut, fig. 7, 6.) 
The principal external features by which Orbitolites 
duplex may be distinguished from Orbitolites niargincdis 
are the annular form and concentric arrangement of the 
segments from the commencement, and the double row of 
peripheral orifices ; whilst the latter character, together 
with the rounded outline of the chamberlets as seen on the 
two faces of the disk, affords a ready means of separation 
from Orbitolites complcmata. In the complex type, as 
will presently be explained, the chamberlets, especially 
those of the later annuli, are more or less elongated in 
the radial direction, and the marginal pores are multiplied 
indefinitely. 
It is almost impossible with our present knowledge to 
lay down the area of the geographical distribution of 
Orbitolites duplex, as distinct from that of the allied forms 
with which it has hitherto been specifically associated, and 
equally difficult to ascertain accurately the limits of its occurrence in the fossil condition. 
To do either would necessitate the re-examination of specimens from all the various 
localities at which the genus is known to exist. The species is found most plentifully 
in the shallow water of tropical seas. It is a prominent form in the Red Sea, where it 
was originally discovered by Ehrenberg, and it occurs in the Mediterranean, at least as 
far north as the coast of Sardinia. Well-marked specimens have also been obtained from 
shore-pools in the Cape de Verde Islands. 
If, as Dr. Carpenter supposes, the Orbulites macropora of Lamarck ( Orbitolites 
macropora, Goldfuss), is referrible to the same species, it is probable that its geological 
range in Tertiary times is analogous to that of Orbitolites complcmata. 
FiG. 7 . — Orbitolites duplex , Carpenter. 
a. Peripheral aspect, showing the double 
row of marginal pores ; magnified 
12 diam. 
b. Transverse section ; magnified 12 
diam. 
c. Portion of the same ; magnified 50 
diam. 
m.p. Marginal pores. 
r.r. Radial stolon passages. 
ac, ac, Annular canals. 
