332 
REVIEWS. 
it, perhaps, the most sharply definable genus of all the polythalamous 
Foraminifera. The more highly specialised forms of Dactylopera 
have a somewhat cylindrical shell, the interior of which is hollow, 
while within the substance of its wall are lodged the chambers, con¬ 
verging side by side, so that their apertures are directed rather 
obliquely towards the axis of the cylinder, and forming a succession 
of annuli or superimposed storeys. The chambers do not communi¬ 
cate with one another internally, but open, separately, into the cavities 
of a very curious ‘ interspace system,’ the lateral prolongations of 
which terminate in two sets of orifices scattered over both surfaces 
of the shell wall. In the closely allied but less elaborately constructed 
Acicularia , the apertures of the chambers are turned towards the 
periphery of the shell. 
With regard to the acervuline modifications which some Forami- 
nifera tend to assume, their very irregularity forbids our making 
any definite observations respecting them in general. One of the 
most singular is offered by the imperfectly polythalamous genus 
Nubecularia , chiefly distinguished for its power of employing the 
surface of attachment which it selects, to form portions of its shell- 
wall. And in Folytrema , which, as Dr. Carpenter shows, is nothing 
but a modified Botaline, the shell assumes a zoophytoid aspect; 
“ for although it sometimes spreads itself as a scaly incrustation oil 
“ the surfaces of shells, corals, &c., it not unfrequently rises from 
“ those surfaces in an arborescent form; whilst sometimes its stalk, 
“ instead of branching, swells into a globular protuberance.” Very 
interesting acervuline forms are also presented by Flanorbulina and 
Tinoporus. 
The form of the septal plane among the Foly tlialamia “is in 
“ direct relation, not merely with the general contour of the shell, 
“ alike in its lateral and in its antero-posterior aspects, but also with 
“ certain of its surface-markings.” Thus, in the case of nautiloid 
shells, the degree to which alar prolongations are developed, and en¬ 
croach externally upon the walls of the previously formed chambers, 
modifies the shape of their septal divisions to a corresponding ex¬ 
tent. As already stated, in some of the more complex Foraminifera 
we find the chambers sub-divided into chamberlets by secondary 
septa running at right angles to the primary ones. In those multi- 
locular forms which are placed in one family with Lagena, the septa 
resemble in structure the rest of the shell-wall: in the higher Per- 
eorata, on the other hand, they.'are completely differentiated from, it, 
and want its characteristic tubuli. The orifices of the septa vary 
considerably in size, form, and situation. They may be single, or 
multiple ; entire, or with a divided and branching margin. And 
in the typical ISFurnmulinida the septal aperture becomes “ a narrow 
“ fissure that is left between the outer margin of the penultimate 
“ convolution and the inner margin of the septum; and alike in 
“ its form, and in its position with regard to the two lateral sur- 
“ faces of the shell, it is consequently quite symmetrical.” In the 
Impereorata, as might be expected, the septal orifices are com- 
