560 
DE. CAEPEXTEE’S EESEAECHES OX THE FOEA^nXTFEEA. 
on the equatorial plane ; and in this manner the increase of the organism in thickness 
is effected. The growth on the two sides of the equatorial plane, however, is seldom or 
never symmetrical ; and that of the more convex portion seems continually tending to 
overpower that of the opposite surface, so that the equatorial plane becomes more or 
less deeply concavo-convex. I have reason to believe that this inequality is due to the 
attachment of the fiat or subconcave base to the surface of sea-weeds or zoophytes ; in 
virtue of which it will naturally happen that the free side will grow faster than the other. 
It is by an excess of this predominating growth that the spheroidal form is acquired, with 
its deep residual cavity, as just now described. 
216. On more minutely examining the structure of the walls of the chambers and the 
mode of communication between their carities, we find ourselves carried back to the 
lower type of Orhitolites and Orhiculina in this particular, — that the septa are not double 
but single, and are formed of a simple homogeneous substance, presenting no vestige 
whatever of that fine tubulation which characterizes the dense almost ivory -like sub- 
stance forming the walls of the chambers in the more elevated forms of this group. It 
will be convenierrt to speak of the partitions between the chambers as JwnzonfaL when 
their general direction is parallel to that of the equatorial plane, and as vertical when 
that direction is perpendicular to it ; their actual directions uill of com-se vary uith the 
curvature of the equatorial plane. The horizontal partitions or floors of the chambers 
are perforated by rounded apertures (Plate XXI. figs. 2, 3, 4) which closely resemble 
those of the shell of a Botalia or a Planorhulina in their size and arrangement ; arrd 
these will allow of free commurrication, by pseudopodial threads of sar'code, between the 
segments that are lodged in the chambers piled orre over the other in a vertical dir-ectiorr. 
The vertical partitions are much thicker, arrd are rrot thus minrrtely and regularly per- 
forated ; but they exhibit a small arrd variable number of large 
apertures (fig. 4, «, «), that lead into the adjacent cells which lie 
in or near the same horizontal plane. I say in or near^ becarrse it 
is seldom if ever the case that the horizorrtal partitions or floors 
of two adjacent vertical piles of cells are on the sarrre level ; and, 
in fact, the typical arrangement (though freqrrerrtly departed from) 
seems to be, that there is an alternation in the levels of the floors 
of adjacent piles (as showrr hr the accomparrying diagram, based on sorrre parts of fig. 3), 
and that every chamber in any pile B normally comrnrmicates with two chambers in each 
of its adjacent piles a arrd c, by orre passage above and the other below the floor that 
divides them. 
217. The relation of this interesting type of strrrctru-e to that of Planorhulina appears 
to me so clear that it carr scarcely be qrrestiorred. For, as in that gerrrrs, the fh'st-formed 
portion of Tinoporus Icevis will eviderrtly corrsist of a flatterred disk, corrsistirrg of rrrrrne- 
rous segments which are arrarrged irr orre plarre, spirally hr the cerrtre of the disk, brrt 
clustered irregularly towards its circrrrrrfererrce, arrd perforated orr both sides uith 
