EOEAMINIEEEA EEOM THE NOETH ATLANTIC AND AECTIC OCEANS. 
191 
may either fill the umbilical cavity, or affect the borders of the umbilical lobes, even to 
their union by a bridge-like growth. Limbation is seldom absent from the border of the 
shell; frequent on the older part of the spire; and not uncommon with the later 
chambers. Figs. 101-103 in Professor Williamson’s ‘Monograph of British Recent 
Foraminifera’ represent a common condition of this typical form. 
The members of Group No. 1 inhabit depths of about 10 to 100 fathoms. The vari- 
eties affecting the shallow water are less neat in their make than those of greater depths. 
Second Group, characterized by P. Auricula and P. oblonga. — In this group the shells 
are far more oblong in shape, from the very rapid increase of size of the chambers ; and, 
as a rule, they are much more delicate and frail than the foregoing, although some small 
deep-sea varieties of this subtype are unusually dense. The septa and borders are rarely 
limbate. The septal face of the last chamber is usually drawn out and inflated, but 
narrow, and, by an umbilical process, overlaps the alar terminations of the older 
chambers. This feature has caused D’Orbigny to class several varieties of this subtype 
as species of his genus Valvulina. In some cases a portion of the septal face near the 
umbilicus is flattened and pertused ; and this feature is usually associated with some 
degree of limbation of the upper septal lines. The whole of the septal face is flattened 
and coarsely perforate in certain forms lying between P. Auricula and P. repanda. The 
aperture is similar to that in Group No. 1 ; but occasionally there is a large subsidiary 
notch. The umbilical lobes terminate in a similar manner to what obtains in the typical 
group ; and the umbilicus, as in the former, may either be closed, by the meeting of the 
lobes, or remain slightly open, or be largely excavate. The varieties in which the last- 
named feature occurs are small deep-sea forms, having dense shell-tissue, a flattened 
hispid upper surface, with flush chambers ; the under surface being gently convex and 
highly polished. 
As a rule, in each of the subgroups of P. repanda , here described, the thick-set vari- 
eties are those that inhabit deep water. 
The members of the Group No. 2 have their best home at 50 to 70 fathoms ; but they 
range from shallow water (algal zone) to 500 fathoms or more. 
The Third Group, including P. Menardii. — This is an assemblage of closely related 
varieties, differing however considerably in feature. Some are very flat and scale-like, 
some conical, some biconvex. The flat forms have usually a somewhat oblong outline ; 
but the members of this group are mostly circular, with indented septal lines ; the 
chambers are sometimes triangular on both surfaces ; though sometimes narrow and 
curved, or oblong, or even square above and more or less triangular below. P. Menardii 
and its nearest allies are margined and limbate on the upper surface, and often granular, 
scabrous, or hispid. These features are less striking in other varieties which pass gra- 
dually into feebly marked, smooth, thick, small, untypical forms. The septal face is still 
large in this group, gently convex or flat ; sometimes sinking in at a spot near the aper- 
ture, which is often boldly notched. The chambers of these shells are fewer than in 
the “repanda-” or “type-group”; but in the better developed specimens they have the 
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