898 
THE VOYAGE OF H.M.S. CHALLENGER. 
ana more or less inflated, small at the commencement and rapidly increasing in size. The 
aperture is a loop-like or comma-shaped slit, on the face of the terminal chamber, 
generally inserted near the distal end, and directed obliquely or vertically downwards. 
These characters are liable to modification in many different ways, and even within 
the limits they embody there is room for considerable diversity of aspect from variation in 
minor particulars. For example, the spire may have many segments in each convolution, 
or it may be only triserial ; or, as often happens, the chambers may be so irregularly 
disposed that the spiral, arrangement is altogether lost; the convolutions maybe so 
drawn out that the test has the contour of a narrow cylinder, or they may be so 
nearly on the same plane that it resembles a depressed Rotalian ; the chambers are 
sometimes inflated and globular, as in Bulimina elegans, and sometimes long and 
compactly fitted side by side, as in Bulimina elegantissima ; and lastly the aperture, 
though the most characteristic feature of the genus, in certain cases exchanges its normal 
shape for that of a nearly circular opening with a border of radiating lines. 
The shell-wall in recent specimens is invariably calcareous, generally very thin and 
transparent, and distinctly though finely perforated. The shells of a number of species 
are ornamented externally, either with raised longitudinal costae, or with marginal 
teeth or spines, still preserving their hyaline texture. But amongst the larger fossil 
forms, especially those of Cretaceous age, the test is liable to become encrusted with cal- 
careous or siliceous sand or other foreign matter, and is consequently often thick and 
opaque, and somewhat rough externally. Undue importance has been attached to this 
character by Reuss and others, who have assigned the subarenaceous species to a 
distinct genus, Ataxophragmium, — a course for which there appears no adequate reason, 
and to which there are many objections. 
In one form or other the genus Bulimina is distributed over the whole world, and 
though it attains its best development on sea-bottoms of moderate depth, that is to say 
at less than 1000 fathoms, it has been met with as low down as 2400 fathoms. 
Its geological range commences with the Upper Tri-as (Parker and Jones) ; it occurs 
in the Oolitic, and is abundant in the Cretaceous formation ; and is found more or less 
plentifully at every stage of the Tertiary epoch. 
Bulimina elegans, d’Orbigny (PI. L. figs. 1-4). 
Bulimina elegans, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 270, No. 10 : — Modele, No. 9. 
„ „ Parker, Jones, and Brady, 1865, Ann. and Mag. Nat. Hist., ser. 3, vol. xvi. 
p. 20, pi. ii. fig. 64. 
D’Orbigny’s model, No. 9, represents a regularly triserial tapering shell, the segments of 
which are numerous and rather small, distinct and more or less inflated or sometimes almost 
globular. It serves as a central type of a somewhat numerous group of recent Bulimina . 
