666 
THE VOYAGE OF H.M.S. CHALLENGER. 
or eight segments ; septation indistinct externally; aperture an arched fissure at the inner 
margin of the final segment, near the periphery on the inferior side. Diameter, x ^th inch 
(0'2 mm.), often less. 
An extremely obscure organism, characterised chiefly by its thick rounded contour and 
minute dimensions. 
Truncatulina humilis is a deep-water form, tolerably abundant at a- few localities. It 
has been obtained at three Stations in the North Atlantic, between lat. 24° and 40° N., 
depth from 1000 to 2750 fathoms; and at two in the North Pacific, between lat. 13° 
and 40° S., depth 1825 fathoms and 2350 fathoms respectively. 
Truncatulina tumidula, n. sp. (PL XCV. fig. 8, a.b.c.d.). 
Test trochoid, more or less depressed ; consisting of three convolutions, the last of which 
is composed of about six segments ; superior face highly convex ; inferior less convex, 
slightly excavated at the umbilicus ; peripheral edge thick and lobulated ; segments 
inflated, especially those of the final convolution. Colour deep brown, except the terminal 
segment, which is generally of lighter hue. Diameter, xro-th inch (0'2 mm.). 
I have been unable to identify the little shells on which the foregoing description is 
based with any previously recognised species. They vary a good deal in minor characters, 
but the minute dimensions, the thick and rounded general contour of the test, the 
ventricose segments, and the dark-brown colour are sufficiently uniform and distinctive. 
The species is tolerably common in the red clay dredged at Station 5, south-west of 
the Canaries, depth 2740 fathoms, but has not been noticed elsewhere. 
Truncatulina pygmcea, Hantken (PI. XCV. figs. 9, 10).- 
Truncatulina pygmcea, Hantken, 1875, Mittheil. Jahrb. d. k: ung. geol. Anstalt, •vol. iv. p. 78, 
pL x. fig. 8. 
The figures referred to on PL XCV. represent a minute variety of Truncatulina 
common in the deposits of deep areas, especially in the “red clay.” The general contour 
of the test, its dimensions, and the disposition of the segments, are almost precisely those of 
Truncatulina pygmcea, Hantken ; but owing to the greater thickness of the walls, the 
umbilical depression is filled up, and the sutures are marked by lines of clear shell- 
substance. These trifling differences are not such as to justify its treatment as an 
independent species, indeed they appear sufficiently accounted for by the deep-water 
habitat of the living specimens. 
Truncatulina pygmcea occurs at three Stations in the North Atlantic, at depths of 
2G75 fathoms to 2750 fathoms; at two in the South Atlantic, 1900 fathoms and 2475 
