REPORT ON THE EORAMINIFERA. 
609 
are founded upon bottom-specimens, which differ in important respects from those taken 
at the surface of the ocean. 
The outer or visible test consists of a single spherical chamber, the exterior of which, 
in surface-specimens, is almost always more or less beset with spines. The spines are 
sometimes so short and minute as to be scarcely perceptible, but more frequently they 
take the form of slender needle-like spicula of considerable length (PI. LXXVIII.; PI. 
LXXXI. figs. 12-14, 24, &c.). In the interior of the chamber of surface-specimens, 
there is usually, if not invariably, a polythalamous Globk/erina - like shell, which is more 
or less apparent through the hyaline walls of the outer test. The internal shell is also 
beset with spines, and its segments are partially or entirely filled with coloured sarcode, 
as shown in the two figures PI. LXXXI. figs. 18, 19, drawn from specimens from which 
the outer test has been removed. The external test of pelagic specimens is a calcareous film 
of extreme tenuity. I have been unable hitherto to obtain any satisfactory measurement 
of its thickness. The dimensions of the test varya good deal ; large examples sometimes 
attain a diameter of -^th inch (0‘84 mm.). The walls are in all cases distinctly perfo- 
rated, but they have nothing resembling a general aperture. 
Bottom-specimens differ from those taken at the surface much more in the thickness 
of the walls than in the external dimensions of the test. The shell is seldom much more 
than 3 ] yth inch (0 - 84 mm.) in diameter, but the walls of average full-sized examples are 
from -^yoth to ^try-th inch (0'028 to 0‘063 mm.) in thickness. The outer surface is never 
spinous, but is either smooth (PI. LXXXI. fig. 25) or granular (figs. 9, 11 ), or even slightly 
tuberculate (fig. 23). The minute specimens which are found in comparatively shallow 
water (fig. 10 ) are commonly of a brown colour, and more or less areolated externally. 
The perforations are usually very distinct, and they are commonly of two sorts, 
differing in point of size (PI. LXXXI. figs. 8 , 22 , &c.). Thus in one example, from which 
measurements have been taken, the larger pores show a tolerably uniform diameter of 
about ! ao nth inch (0'021 mm.), the smaller series of about goVoth inch (0‘005 mm.); 
whilst in another the diameters are T ^^th inch (0'013 mm.) and 4 (youth inch (0'0063 
mm.) respectively. But no general rule can be laid down, inasmuch as in a certain 
proportion of specimens the pores are practically all alike, presenting an intermediate 
diameter of about 3 3 V (jth inch (0’0077 mm.). 
D’Orbigny describes and figures the aperture of Orbulina universa as a rounded 
orifice, but states that he had only been able to find it in about one-sixth of the specimens 
he had collected. After the careful examination of thousands of bottom specimens I 
have not succeeded in obtaining one with an orifice that can be affirmed with any 
certainty to be the natural aperture. Openings approximately circular are occasionally 
met with, sometimes more than one in a shell, but the edges are invariably rough and 
abrupt, as though the result of fracture (PI. LXXXI. fig. 20), and they lack the smooth 
neatly-finished aspect which is a common feature of the mouth of a Foraminifer. Under 
