466 
DR. M A NT ELL ON FOSSIL FORAMINIFERA. 
chambers, of mineral matter of a different colour from the surrounding- matrix ; a 
circumstance of common occurrence, not only in Ammonites, Nautili, and other 
chambered Cephalopoda, but also in Polythalamia, which are frequently filled with 
chalk, flint, and silicate of iron*. The usual appearance of the fossil Rotalise filled 
with chalk, when viewed by transmitted light, and rendered semi-transparent by 
Canada balsam, is shown in fig. 6. 
The unequivocal organic structure, however, discernible in the substance contained 
in the cells of the Rotalise by a highly magnifying power, and of which no traces are 
observable in the mineral casts, and the identity of appearance in the fossils and 
the corrugated animal body in the Levant specimens, convinced me of the correct- 
ness of the explanation I had suggested. I therefore resolved to follow up the in- 
quiry by an examination of Rotalise from chalk, in the expectation, that if the shell 
Avere dissolved by acid, indications of the body of the original might be detected in 
the residuum, in an unmineralized condition. After many fruitless experiments, I 
succeeded in procuring several examples of the soft bodies of Rotalise in an extra- 
ordinary state of preservation, from the grey chalk of Folkstone. 
To Mr. Henry Deane of Clapham Common, an able chemist and microscopical 
observer, I am indebted for the most illustrative specimens ; accurate figures of which, 
draAvn by Mr. Mounsey, and M. Dinkel, are subjoined. These relics were obtained 
by subjecting a few grains of the cretaceous rock to the action of Aveak hydrochloric 
acid, by which means the calcareous earth, and the shells it enveloped, were removed ; 
the residue consisted of particles of quartz, and of green silicate of iron, Avith Avhich 
the chlorite chalk abounds, and numerous remains of the soft parts of animalcules. 
A small portion was then prepared in the usual manner Avith Canada balsam, and this 
was found to contain many Xanthidia, and the Rotalise hereafter described. 
I have not had an opportunity of examining the structure of the living Rotalise ; 
but from the recent observations of M. Ehrenberg, it appears that the organization of 
these minute animals is very simple, and has no relation Avhatever to that of the 
Cephalopoda, as was formerly conjectured. The body is inclosed Avithin the shell, and 
occupies not only the outer chamber, but also all the cells contemporaneously ; and 
the shell is pierced all over with minute pores like a sieve (see fig. 15), through which 
tentacula protrude ; there are also several soft transparent feelers or pseudopodia, 
which are instruments of locomotion. The shell of the Rotalia, therefore, though 
presenting the general form and chambered structure of that of the Nautilus, is essen- 
tially different ; for while in the shell of the latter, the animal occupies only the outer 
chamber, and all the internal compartments are successively-quitted empty dwellings, 
in the Polythalamia the body distinctly fills up simultaneously all the cells. When the 
* In these cases, the shells were probably either empty when enveloped in the liquid chalk or flint, or speedily 
became so by the decomposition of the soft parts ; but in the instances under examination, I conceive that the 
live animal was suddenly enclosed in its shell, and hermetically sealed, as it were, by the investing mineral 
matter, and thus the usual putrefactive process prevented. 
