ON THE GENUS POLYMORPHINA. | | 199 
Considering that there is abundant evidence to show that the fossiliferous beds were 
generally deposited at a less considerable depth than that represented by the only series 
of Mediterranean soundings available for comparison, these figures require much stronger 
evidence than any that has yet been adduced against the theory of “continuity " to 
warrant the specific separation of recent and fossil specimens merely on the ground of 
age. The fauna of the Mediterranean area happens to be convenient for reference, because 
the data are already published ; but the same conclusions are arrived at on a comparison 
of Recent and Tertiary Foraminifera, whatever the source. In the lapse of time, owing to 
causes partly well understood, partly only conjectured, some forms have died out or have 
gradually lost their importance, some have been replaced by others, and relative size and 
frequency have varied with altered climatal conditions; but with these exceptions the 
fossil Rhizopod fauna of the Tertiary and Quaternary epochs is the living Rhizopod fauna 
of similar depths of the present sea-bottom. 
If these conclusions be accepted, the same must be held true of preceding geological 
times; for we find also in the microzoic rocks of the Secondary period a considerable 
proportion of the same “species” (i.e. forms having the same zoological characters) ; 
indeed, judging from recent researches on the deep-sea bed, it seems clear that we have 
at the present moment a Chalk area, with characteristic Rhizopoda, in process of forma- 
tion in some parts of the North Atlantic. 
In the comparison of the Mesozoie with the Recent, or even with the Tertiary fauna, 
a larger margin must be granted for different external conditions; and this allowance 
must be still further increased if the same question be discussed in respect to the animal 
life of the Paleeozoic era. We may trace back even in the strata of those very early 
times, certain types of Foraminifera that are living at the present day in our seas. Thus, 
notably, the Vodosarie and Textularie abound in certain parts of the Permian Limestone 
. of Germany and England. A Textularia, undistinguishable from T. sagittula, is found in 
the Carboniferous Limestone; and a very similar form, possibly a variety of the type, is 
not rare in some parts of the same formation ; and these occur together with the Planor- 
bulina-like shell known as Endothyra, which is often seen in sections of compact Moun- 
tain limestone. Indications of a still higher Foraminifer, possibly Nummulina, have 
been noticed in both English and Russian limestone of Carboniferous age. 
It is true that other forms are lost to us, so far as researches have yet extended; 
but even these tend rather to augment than diminish the cogency of our argument. Thus 
Fusulina, a genus which Dr. Carpenter has shown to be closely related to Nummulina, 
isa characteristic fossil of certain Paleeozoic limestones of Russia and North America ; 
and in the Devonian and Silurian rocks the massive Stromatopora appears with simple 
Foraminiferal structure. Other forms of Protozoa existed in these or even earlier 
ages, if we accept Professor Ehrenberg's conclusion that the green kernel.like grains 
occurring in the green Lower Silurian sand of St. Petersburg are casts of the cham- 
bers of Foraminifera. Lastly, structures essentially Foraminiferal (Lozoon) are traceable 
in the Lower Laurentian limestones, the lowest and oldest of the known geological 
series. : 
_ These few extinct types, the representatives probably of many, stand in the closest 
