REPOET ON THE FORAM I.NIFEB A. 
147 
Biloculina tubulosa, Costa (PI. III. fig. 6 ci.b.c.). 
Biloculina tubulosa, Costa, 1856, Atti dell’ Accad. Pont., vol. vii. p. 309, pi. xxiv. fig. 7. 
Under the above name Costa has described a variety ot Biloculina allied' to 
Bdocnlina bulloides, but differing from that species in having a wide fissure or depression 
on both faces of the test on the line of union between the two outermost segments. It 
is obvious that a shell so constructed can only remain Biloculine so long as the depression 
is regular, and equal at the two sides, and that any obliquity is liable to expose a portion 
of the ante-penultimate segment, or in other words, to render it Triloculine. In point of 
fact, the specimen figured by Prof. Costa is in the latter condition. 
In one of the Challenger dredgings a form with similar peculiarities, which may con- 
fidently be assigned to the same species, is tolerably abundant. The specimens are 
of considerable size, often -^yth inch (1*25 mm.) in length. In their young state 
they are generally Biloculine, and sometimes retain the same condition when fully 
grown ; but more commonly in the adult shell a small portion of the surface of a third 
chamber is exposed, as shown in the drawing, fig. 6, c. 
An analogous passage form is figured by Dr. Karrer, from the Miocene of Kostej 
(Sitz. d. k. Akad. Wiss. Wien, vol. lvii. pi. i. fig. 11), under the name Triloculina inter- 
media ; that, however, appears to be more distinctly Triloculine than the recent specimens, 
and the margins of the two outer segments are subcarinate. 
Biloculina tubulosa is common in one of the dredgings off Kandavu, Fiji Islands ; 
depth, 210 fathoms. 
As a fossil it is rare in the Pliocene deposits of Lequile and Ischia, Italy (Costa). 
Sp i) ‘oloculina, d’ Orbigny . 
Miliolites, pars, Lamarck [1804]. 
Miliola, pars, Defrance [1824], Bronn. 
Spiroloculina, d’Orbigny [1826], Roemer, Macgillivray, Reuss, Ehrenberg, Bornemann, Costa, 
Williamson, Parker and Jones, Karrer, Carpenter, Seguenza, Brady, Schwager, Robertson, 
Schulze, Terquem, Bertkelin, Wright, &c. 
In the typical Spiroloculina the segments are Milioline — that is to say, each extends 
the entire length of the shell, and the position of the aperture is alternately at either end 
— they are arranged on one plane, and the whole of them are visible on both sides of the 
test. These characters serve to distinguish it from Miliolina, in which the plane of growth 
changes with each fresh segment, and from Biloculina , in which, though the chambers are 
arranged symmetrically on one plane, they are broad and embracing, and each encloses 
all the previous segments on the same side. 
But whilst these are typical characters, and in most cases sufficient for the discrimina- 
tion of the subgeneric groups, they are open to considerable variation. For example, in 
