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THE VOYAGE OF H.M.S. CHALLENGER. 
made, and correctly in a certain sense ; but in such cases the subordinate groups, though 
indistinct in outline, and often overlapping at their edges, have independent characters 
more or less marked, coincident with certain conditions of locality, latitude, depth, or 
geological age, none of which can be adduced with reference to the Peneroplides. Nor 
is there any genus of Foraminifera, embracing so great a range of external form, in which 
the morphological sequence is at once so simple and complete, so free from complications 
arising from divergent series, or from minor distinctions depending on questions of 
surface-ornament and the like. In stating these facts I am doing little more than 
repeating conclusions expressed at various times, by my colleagues Dr. Carpenter, and 
Messrs. Parker and Rupert Jones. Wherever Peneroplides abound, this wide variation 
exists, and nothing can be more easy than to pick out a number of striking specimens 
and give to each a distinctive name, but in no other way can they be divided into 
“ species.” The foregoing remarks refer primarily to the well-known living representa- 
tives of the type. There are, nevertheless, certain rare Tertiary forms, some of them attain- 
ing large dimensions and probably subgenerically distinct, concerning which little can be 
said at the present moment. The species referred to have been specially studied by 
M. Munier-Chalmas, to whose kindness I am indebted for specimens, but the results of 
his investigations respecting them have not yet been made public. 
In the foregoing summary I have attempted nothing more than to collect references 
to the various modifications described by previous authors under specific names, and 
to arrange them round a few of the more easily recognised forms. The groups so 
constituted, each represented by a sort of type, are, zoologically speaking, of something 
less than subvarietal value, but they possess a certain amount of convenience, and at 
any rate the arrangement gives a succinct view of the morphological range of the genus. 
The typical Peneroplis pertusus ( b .) is represented by a compressed planospiral shell 
of about three convolutions, the width of the chambers increasing somewhat rapidly. 
The convolutions are sometimes investing and nautiloid, sometimes evolute and more or 
less visible to the centre. The degree and comparative rapidity of the widening of the 
spire vary with every specimen, and find their extreme development in the thin outspread 
shell of Peneroplis plancitus (a . ). 
On the other hand, there are a number of modifications dependent on the change 
from a spiral to a rectilinear plan of growth, and the consequent production of a more 
or less crosier-shaped test. The intermediate condition, in which the shell is still com- 
pressed and the rectilinear portion increases very gradually in width, is exemplified in 
one of Batsch’s figures, and may be accepted with the name Peneroplis arietinus (c.), as 
the type of the third series. 
But the more distinctly crosier-like varieties ( Peneroplis cylindraceus, d.) lose the 
compressed contour and the tendency to widening of the chambers ; and, after the 
spiral commencement, put on a straight line of segments of nearly uniform size, and oval 
