566 
DE. CAEPEXTEE’S EESEAECHES OX THE EOEA^nXITEEA. 
227. Internal Structure. — On breaking-away a portion of the external wall of the 
last-formed chamber, so as to lay open its interior (as shown in fig. 8), we find that its 
cavity is closed-in on evei’y side by its shelly walls, except where it has communications 
(Z», c) with the apical aperture ; and each principal chamber is partially subdivided by 
a system of shelly septa, of which some are more and others less complete. The more 
complete of these secondary septa (fig. 8, e, e\ resemble the principal septa [d. dP) 
which separate the cavities of the chambers, in rmnning from the base towards the apex 
of the cone; they divide the lower portion of each chamber into three, four, or more 
digitations, which are sometimes marked by an extermal lobulation, as shown in fig. 5 ; 
they stop short, however, aborrt half or two-thhds of the way towards the apex, lea^ing 
the upper third or half of the chamber undivided. Some of these septa do not reach 
the opposite surface of the chamber; and the least complete form a sort of 
network of ridges slightly projecting from the inner surface of the outer wall into its 
cavity (as shown in vertical section at b, b, b, fig. 15), and there marking out an ai’eola- 
tion which corresponds to that of the external surface. The areolae of the internal 
surface, however, are concave instead of convex ; and the punctations, which are wanting 
on the ridges, are set more closely on the depressions between them. The reason of tliis 
peculiarity in their distribution will be presently seen (^ 229). 
228. The cavity of the last chamber communicates with the external orifice by a 
passage of considerable size ; and the wall of this passage is distinctly continued as an 
irregular ring around the apical aperture, so that this aperture may be considered in 
one sense (as described by Dr. Geay) to belong to the last chamber alone. But it would 
be more correct to say that each cell as it is formed conceals, than (with Dr. Geat) that 
it closes, the aperture of the preceding cell ; for a careful examination shows that the 
external aperture or vent is the termination of an irregular vertical canal, formed by the 
superposition of the oral rings of successive cells ; and that through this canal the 
previously formed cells retain their original connexion A^ith the exterior. In some of 
Mr. Paekee’s specimens, the oral ring is extended upwards into a tube or siphon at 
least equal in length to the radius of the cone. The general disposition of the chambers 
around the central canal is well shoAvn by sections of the cone talcen parallel to its base 
(fig. 7); such sections, however, may only bring into rtew the last or superficial whorl; 
and they will generally show only one or frvo chambers in commimication ^rtth the 
vertical canal, the communicating passage of each chamber being on a difierent plane. 
229. The foramina which pierce the outer wall of each chamber are of considerable 
size, as compared with the minute tubuli of Cycloclypeus and OpercuUna (see 103, 
154), and they are not nearly so closely approximated ; m both respects they correspond 
closely with the foramina of the ordinary Botaliw and Globigennw. In fig. 12 they are 
shown as they appear in a section traversmg the wall someAvhat obliquely to its surface, 
whilst in fig. 15 they are shown as they appear in vertical section ; and in each case they 
are seen to present an annulated appearance, which is due to constrictions of the tubes 
at tolerably regular intervals. These tubes generally pass direct from one surface to the 
