154 
THE VOYAGE OE H.M.S. CHALLENGER. 
The test of Spiroloculina tenuiseptata resembles at first sight that of Spiroloculina 
limbata, but in reality the conditions are exactly reversed, that is to say, the raised portions 
of the surface represent the chambers, and the intervening depressions the shelly septa. 
M. Terquem has figured a Spirillina (or Cornuspira ?) with the same peculiarity 
developed to an even greater degree under the name Spirillina lateseptata , 1 in wdiich a 
thin, broad, horizontal plate separates the successive convolutions of the spire. In the 
present species the width of the septa varies a good deal, and it is not uncommon to find 
a small portion of the final segment left unattached at its inner margin. In one minute 
specimen (fig. 6) the thin shelly plate, which is unusually broad in the earlier portion of 
the test, is incomplete ; and the later segments are entirely free and separated from the 
previous convolutions by an open space. 
In the recent condition Spiroloculina tenuiseptata is a rare form, only found 
hitherto at three localities : — off Ki Islands, 580 fathoms ; offKandavu, Fiji, 610 fathoms ; 
and the Mediterranean, 1200 fathoms. 
One or more of the specimens figured in von Schlicht’s work on the Foraminifera of 
the Septaria-clay of Pietzpuhl, pi. xxxvii. fig. 27, &c., named by Reuss Spiroloculina 
dorsata, appear to belong to this species. 
Spiroloculina acutimargo, n. sp. (PI. X. figs. 12-15). 
Test oval, complanate, thin, slightly convex on both sides ; peripheral margin acute 
or carinate, extremities obtuse or slightly rounded. Chambers arcuate, angular or 
carinate at the outer margin, either slightly embracing or separated by the intervening 
wing of the previous convolutions. Aperture small, sometimes in a produced tubular 
extension of the final segment. Length, -g^th inch (0’85 mm.). 
Referring to Plate X. — figures 12 and 13 represent fully-grown typical examples of 
this species ; fig. 14, an immature shell ; and fig. 15, which is taken from one of com- 
paratively large size, an old and worn specimen of the same. Amongst those forms of 
Spiroloculina that have the aperture in a produced neck, instances are by no means rare 
in which the shell is perforated at intervals on the median line, little open spaces being 
left at the ends of the segments, especially in the later convolutions. This condition, 
which is easily accounted for, is shown in fig. 15 to a somewhat marked degree, and it 
may often be observed, though to a less extent, in specimens of Spirolocidina grata (fig. 
16 of the same plate). 
Spiroloculina acutimargo has been dredged off Bermuda at a depth of 435 fathoms ; 
at four Stations in the South Atlantic, 350 to 1425 fathoms ; and at three localities in 
the South Pacific, 15 to 255 fathoms; it has also been found in shore-sands collected on 
the east coast of Madagascar. 
) Anim. sur la plage de Dunkerque, pi. i. fig. 6. 
