REPORT ON THE FORAMINIFERA. 
413 
It is exceedingly difficult to separate such forms as those portrayed in figs. 12 and 
13 from the attenuated varieties of Virgulina; but the apertures appear to indicate 
more direct affinity with the genus Pleurostomella ; and in the shape and disposition of 
the segments the specimens agree with the Pleurostomella subnoclosa of Reuss. 
This particular modification of the type has been met with at two Stations in the 
South Atlantic, in mid-ocean, 2200 fathoms and 2350 fathoms ; and at two in the South 
Pacific, west of Chili, 1825 fathoms and 1375 fathoms respectively. 
As a fossil Pleurostomella subnodosa occurs in Cretaceous deposits of various age, in 
North Germany and Bohemia (Reuss, Marsson). 
Virgulina, d’Orbigny. 
Virgulina, d’Orbigny [1826], Romer, Bronn, Reuss, Czjzek, Egger, Parker and Jones, Ivarrer, 
Brady, M. Sars, Hantken, Schulze, Robertson, &c. 
Bulimina, pars, Bailey [1851], Parker and Jones, Williamson. 
Pohjmorjpliina , pars, Costa [1856]. 
Excepting the genus Lagena, there is no group of hyaline Foraminifera the knowledge 
of the varietal modifications of which has received larger accessions from the study of the 
Challenger material than that comprising' the aberrant forms of Bulimina,, included under 
the generic or subgeneric terms Virgulina and Bolivina. 
In both of these genera the divergence from the typical Bulimine structure is the 
result of a tendency to assume a simpler mode of growth, — to become, in fact, more or 
less biserial in the arrangement of their segments, whilst still retaining the characteristic 
Bulimine aperture. It is impossible to separate the two groups from each other, or indeed 
from the typical Bulimince , by any well-defined or constant peculiarity ; ell that can 
be said by way of distinction is that Virgulina is more Bulimine and less Textularian in 
the disposition of its segments than Bolivina, and that Bolivina, on the other hand, is 
more Textularian and less Bulimine. 
This distinction may generally be recognised amongst the biserial varieties of 
Virgulina in the inequilateral setting-on of the chambers, and the consequent difference in 
the appearance of the two lateral faces of the test, whilst in Bolivina the two sides are 
nearly alike. The structural features of the test render it comparatively easy to associate 
Virgulina with its type ; but Bolivina often only betrays its affinity by the aperture, 
which takes some form within the range of variation to be found in Bulimina itself. 
Amongst the varieties of Virgidina are to be found all the links connecting Bolivina 
with the typical Bulimina. 
The geographical distribution of the genus Virgidina is world-wide, and does not 
appear to be influenced by latitude or depth of water. Its geological history scarcely 
extends to the commencement of the Tertiary epoch, but in the Miocene and subsequent 
formations the genus is of common occurrence. 
(ZOOL. CHALL. EXP. — PART XXII. 1884.) 
Y 53 
