4 DE. CAEPENTEE’S EESEAECHES ON THE EOEAAONIEEEA. 
Mr. CUMINS’S Phffippine CoUection ; whilst the most n^erous were kmdly famished 
me by Mr. J. Gwyn Jepferys from his dredgings in the Grdf o eno . 
hereafter find that, as in the case of OrUtolUes, particular varieties of conformation 
prevail, though by no means exclusively, in particular localities. ^ u- u 
123 ExtLal au™otera.-The ordinary form of the shell of (of which an 
ideal representation is given in Plate I. fig. 2) is an extremely flat spue of about fao 
turns and a half, opening out lapidly in its last half turn (Plate II. ). 
young shell, each whorl is merely adherent to the preceding, so that the fust-formed 
portion is not concealed by the subsequent growth ; but it very commonly happens t a 
the last whorl spreads itself out to such a degree as partially to mvest the preceding 
(Plate 11 figs 1 3), the extension towards the centre, however, seldom reac mg so ar 
as to conceal ihe original umbilicus. Although this lateral extension is sometimes con- 
fined to the inner margin of the spire, as is seen in fig. 1, yet it often occurs along the 
outer margin also, as is seen in fig. 3; being usually Umited, however to the last fom 
or five chambers. But sometimes, instead of opening out and partially investing the 
previous whorls, the spire is prolonged in a straight line, and several of its successiie 
chambers present little or no progressive increase in size (Plate II. g. ), oug even 
in this variety the last four or five chambers are often seen to spread themselves out 
rather suddenly, so as to extend along the inner margin of the straight portion. Between 
these difi-erent extremes of conformation, every intermediate gradation presents itse . 
124. The surface of the shell is very strongly marked by depressed bands whic 
indicate the place of the septa between the chambers; and between these septal bands 
the walls of the chamber's rise in flattened arches. In a direction transverse to t e 
septal bands, we almost uniformly obsei-ve a strongly-marked striation ; the stnee ninnmg 
pai-allel at tolerably regular intervals, which average about TAoth of an inch, torn one 
septal band to another. This striation, which imparts a very characteristic physiognomy 
to these minute sheUs, seems due to a sort of plication or ridge-and-furrow anangement 
of the sheUy wall (Plate II. fig. 20), which may not improbably have the effect of 
imparting to it increased strength. The plication generaUy disappears at the junction 
of the walls of the chambers with the septa; and consequently we do not usually see it 
at the mouth when the shell is viewed endways. Sometimes, however, it is oontinued 
on to the septum itself ; and its character is then extremely well displayed, as in Plate 11. 
fi.. 16, which, however, represents not the typical form, but one of the varieties to be 
hereafter noticed. On the prominences of the plic®, there are frequently to e seen 
rows of extremely minute puncta (fig. 20) ; these, however, are not the apertui'es of pas- 
sages through the shell, as might not unnaturally be supposed; but are, hke the punc- 
tations of OrUmlinu ("^ 88), mere depressions of its surface, -as I have ascertamed by 
the careful examination of very thin sections. It is remarkable that the phcation of 
the shell is sometimes wanting, though the punctations may still present themselves m 
rows, as shown in fig. 23 ; whilst in other cases, not only ai'e the plic® deficient but e 
punctations are distributed uniformly over the entire surface, as shown m fig. 24. Ihat 
