216 Mr. Henry B. Brady o» 
Transactions’ (vol. clv. p. 422). These go far to explain the 
peculiarities of the living fauna of the same area. In most o 
our brackish localities the living species are presumably the 
offspring of specimens which have been washed in and gra- 
dually acclimatized; but in the Fens the present Rhizopod 
fauna must consist in great measure of the direct representa- 
tives of those which flourished under the earlier more nearly 
marine conditions; and hence, with some allowance for pos- 
sible change of climate, the relation of the living to the sub- 
recent fauna is one which has been determined by gradual 
alteration in the physical aspects of the country, of which the 
chief result, so far as affects animal life, has been the lessened 
proportion of saline constituents in the water. The following 
genera, which were living in the Fens at this earlier era, have 
now totally disappeared, viz. :— Cornuspéra, Nodosaria, Uvi- 
gerina, Spirillina, Textularia, Virgulina, Bolivina, Pulvinu- 
ina, Discorbina, and Patellina; and it is a noteworthy argu- 
ment against the probability of any material change in climate 
that the whole of these, except Spirillina, still live in brackish 
water at portions of our coast nearer the open sea than the 
Fens now are. On the other hand, no single new genus has 
appeared during the period, if we except a straggling specimen 
or two of Biloculina. The Miliole generally have become 
commoner, whilst the whole family of the Lagenida have 
diminished in numbers; but, with these exceptions and the 
disappearance of the types above enumerated, there is a 
striking agreement between the present and past Rhizopoda 
of the Fen area. Our analysis need not extend to details 
respecting species, which may be gathered from the Table, 
further than to note that, out of forty-one specific and varietal 
forms found subfossilized in the clay, twenty have survived the 
changes alluded to, and the few new forms which now exist 
generally represent depauperated conditions of certain of the 
Ider types. 
A comparison of specimens derived from marine and brackish 
sources, in species common to both, has considerable bearing on 
the connexion between the various groups of Rhizopoda. The 
effect of change of habitat is more marked in some genera than’ 
in others; but it may be generally stated that as the proportion 
of salines in the water decreases, the tests of the Foraminifera 
show a corresponding deficiency in calcareous matter. 
In the Miliolida the deficiency is sometimes evidenced 
merely by the diminished thickness of the shell-wall, as often 
seen in Quingueloculina subrotunda ; but it takes quite another 
character in the composite or almost chitinous test of Q. fusca. 
