700 
THE VOYAGE OF H.M.S. CHALLENGER. 
dependent upon local conditions, of which depth of water is probably the most important. 
Setting aside the six Stations referred to, at which both forms occur, the average depth 
of nineteen recorded localities for Pulvinulina elegans is 340 fathoms; that of twenty - 
three Stations at which Pulvinulina partschiana has been noted, 1000 fathoms. 
Speaking in general terms, the home of the former is from the 
littoral zone to a depth of 600 or 700 fathoms, that of the latter 
from about 300 fathoms to 2000 fathoms ; whilst passage-forms 
are commonest at 800 to 1300 fathoms. 
The differences in external appearance are chiefly due to the 
thickening of the shell wall. Deep-water specimens of Pul- 
vinulina partschiana exhibit a mode of growth very similar 
to that of a Nummulite — the alar flaps of each new chamber 
spreading over the lateral surfaces, and giving rise to the 
lamination of the walls shown in the annexed drawing of the 
transverse section of the test. With increased age the test looses 
translucency and becomes opaque-white and dull externally. 
The normal aperture of Pulvinulina elegans (and partschiana) 
is a fissure at the inferior margin of the final chamber, close to the 
line of union with the previous convolution. But this is not an 
invariable character, and specimens from certain localities exhibit 
a somewhat anomalous feature in the form of a supplementary 
orifice. This has the aspect of a long, arched, linear slit, imme- 
diately within the peripheral margin of the final segment on the inferior side, and parallel to 
it — that is to say, an opening between the carinal border and the proper wall of the terminal 
chamber. The peculiarity referred to was pointed out to me several years ago by my friend 
M. Schlumberger, and it has since formed the subject of a “ Note ” by M. Berthelin ( loc . cit.) 
The specimens in which it occurs are identical in every other respect with the typical form, 
and in some cases at any rate still retain the normal aperture in addition. M. Berthelin, 
speaking chiefly from fossil specimens, has observed the coexistence of two apertures, but 
states that the orifice which occupies the ordinary position is of far less importance than 
that at the periphery. He also states, what is an evident fact, that the peripheral aperture 
is obliterated when a new chamber is formed ; and this of itself appears sufficient evidence 
that the connection between the segments is maintained by stoloniferous orifices in the 
normal position. More recently M. Schlumberger has described living specimens pos- 
sessing the same peculiarity under the name Rotalina pleurostomata (Feuille des Jeunes 
Naturalistes, ann. xiii. p. 27, pi. iii. fig. 5), The nearest analogy to the phenomenon in 
question is perhaps to be found in Truncatulina rostrata ; and in this species, as already 
explained (p. 669), the peripheral or supplementary aperture has not been satisfactorily 
traced beyond a few of the later segments. Terquem has formed a quasi-generic group, 
Fig. 21. — Transverse section of 
Pulvinulina partschiana, 
showing the thickness of the 
shell-wall and its Nummuline 
lamination. Magnified 40 
diameters. 
