20 DB- CAEPENTEE’S EESEAECHES ON THE EOEiAHNIPEEA. 
disconnected from one another. In Plate I. fig. 3, an attempt is made to bring together 
in an ideal representation the most important features of the ^ 
„lma, as disclosed by these two methods of examination ; the wanantj for 
being supplied by the delineations of the separate parts that are given m othei figures, 
which are all taken from preparations in my possession. 
151 Owing to the circumstance that large specimens of Overmhna are rardy d eve 
quite flat, it is next to impossible to make a section through the median plane that sha 
traverse all the whorls to the central cell; a sufficiently near approach to this.^howevei, 
has been made in the section represented m Plate VI. fig. 3, and Plate IV. g. , 
Ling into view the general disposition of the chambers. This is much 
woufd be supposed from a superficial examination of the exterior, f “ 
certain general average in the proportion which their long diameter (that is, the biea 
of the whorl) bears to the short (or distance between the septa), which may be stated 
about 4i to 1, this is by no means constantly maintained, the long 
times as much as 7 times, and sometimes no more than 2^ times, the s oi . 
nary course of the septa, too, is often strangely departed from, as is seen in JT 
Ho- 3 There aie few individuals which do not present-besides abnormal sinuosities, 
heater or less in degree— very marked in-egularities in the conformation of the cham- 
ters, analogous to those which I have described in MmmuMes* Frequently a septum 
instead of passing continuously from the inner to the outer margin o e w oi , s op 
short without reaching the latter, and bends backwards to join the last-formed sep u^ 
and sometimes a second septum unites itself to the first in the same manner, as shov™ 
at « Plate VI fig. 3. The abortion is often still more marked ; thus at b we see thie 
interrupted, of which two do not traverse half the distance, and the thud 
not a quarter, thus dividing the space between two complete septa 
bers along the inner margin, and one large irregular chamber extending to outm. 
Another case of the same kind is seen in an earlier part of the same whoil, m 
Fig. IV. an additional illustration on a larger scale is given of the like megi an j, 
Eig. IV. 
Irregular dispositiou of septa iu OpercUnu «, «. normal apertures at inuer margin of spu-e ; 
I, V, i", apertures of communication between abnormally divided cbambeis. 
the purpose of showing the arrangement of the communicating passages. Generally 
speaking, the more nearly we approach the centre of the spire, the more regu ai y o 
we find the septa disposed, until we come into close proximity wit i t e cen la ce 
* Quarterly Journal of tbe Geological Society, vol. vi. 1850, p. 23. 
