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X. A Monograph of the Genus Polymorphina. By Henry B. Bravy, F.L.S., 
W. K. PARKER, F.R.S., and T. RUPERT JONES, F.G.S. 
(Plates XXXIX.-XLII.) 
Read June 3rd, 1869. 
INTRODUCTORY. 
PERHAPS no genus of the Foraminifera, embracing individuals so widely different in 
conspicuous characters, presents at the same time so unbroken a series in the differentia- 
tion of its successive links as the group brought together by D’Orbigny under the name 
POLYMORPHINA. 
Whilst its interest is heightened rather than diminished by this fact, the difficulties in 
the way of satisfactory systematic arrangement and subdivision are considerably aug- 
mented; and as successive observers have pursued independent paths, with but little 
reference to what has gone before, the nomenclature of the genus has lapsed into almost 
inextricable confusion. This condition is obvious enough to any one who has attempted 
to name even a small collection of Polymorphine ; but in recent investigations for our 
« Monograph of the Foraminifera of the Crag," it was found to be a cause of constant 
embarrassment. The extraordinary predominance of specimens belonging to the genus 
in the later Tertiary beds of our Eastern Counties, and their wide range of variation, 
rendered it desirable, under these circumstances, to make a critical examination of all 
the *species" previously described, before attempting to assign trivial names to the 
forms which presented themselves from this particular source. The exhaustive survey 
of the group thus commenced has been a more considerable undertaking than was at first 
anticipated; and its results appear to be of sufficient importance for embodiment in a 
separate memoir ; and this it is that we now lay before the Society. An attempt has been 
made to arrange the various members of the genus in something like a natural sequence ; 
whether it has been successful in any thing more than in the reduction of a disorderly 
mass of ill-defined and chiefly needless “species” into manageable compass by the adoption 
of larger subdivisions than those previously recognized, it is for others to judge. 
The question of the importance to be attached to minute and very variable external 
characters is so much one of opinion, that the acceptance of any series of conclusions in 
respect to it cannot be urged on quite the same basis as that which may properly be 
claimed for results admitting of more direct proof. Observations on a very large number 
of specimens, drawn from a wide range of distribution both geographical and geological, 
and a comparison of their morphological characters with analogous variations in allied 
genera, form the groundwork of the views now advanced ; and we may at least claim fer 
them whatever consideration is due to careful study within these limits. 
It may be well to state at the outset the principles which have been held in view 
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