OF SOUTHERN INDIA. 3 
we shall use, in the course of our descriptions, the generally accepted expressions ; 
to avoid, however, any misapprehension a few remarks will probably not be out 
of place. 
Tn all our figures, we have adopted the position with the apex of the shell above 
and the aperture below and in front of the observer. Strictly speaking the choice of 
this or of the reversed position, as used chiefly by French Conchologists, depends 
merely on the habit to which a naturalist has been accustomed. Neither of these 
positions, as is well known, is throughout strictly natural or corresponding with 
that of the living shell, and as regards illustration, the one has no peculiar 
advantage over the other. In a few swimming species, the reversed position may 
be thought more natural, while the regular position, with the apex above, is in the 
greater number of conical shells not only natural, but as regards certain fixed 
terms in common use is decidedly preferable. 
As to the different forms of the shells, the expressions used need no farther 
explanation; they are all very familiar and easily understood. The name of ‘ body 
whorl’ applying to the ‘last whorl’ (anfractus ultimus) will be omitted, as it has 
no real significance in the Gastropoda. 
Speaking of the aperture, the expressions ‘below’ and ‘above’ will also be 
omitted, because they are liable to cause misunderstanding in the reversed position 
of the shell, and the respective expressions ‘ anterior’ and ‘ posterior’ will invari- 
ably be used. The same remark applies to the names of ‘right’ and ‘left’ 
lip or peristome, in place of which the corresponding terms of ‘outer’ and ‘inner’ 
or ‘columellar’ lip are less liable to cause confusion in cases, when any one desires 
to refer to a figure, for which elsewhere a reversed position has been chosen. If 
not particularly noticed, we shall understand by ‘inner’ lip, that portion of the 
peristome, which adheres immediately to, or covers partially, the preceding whorl, 
and which is also often called the columellar lip. The posterior angle of the 
aperture marks, generally speaking, the posterior junction of the outer and inner 
lip, which are here either wvited or separated. 'The anterior junction of these two 
requires, however, often a special explanation in the different groups, if it is not 
clearly marked by the anterior canal, or at least a slight notch of the aperture, as in 
the greater number of the Prosobranchia. 
Considerable difference exists as regards the terms, which are used for the 
designation of the so-called ‘umbilicus.’ We shall, in all cases, cease to use the 
word ‘perforated,’ because there is in reality scarcely a single Gastropod shell, 
which can be truly called perforated, and because the original meaning of the 
term, as first introduced, has in the course of further enquiry been so variously 
applied, that the simple use of the word now leaves an observer in doubt, or, 
when no special explanation of the expression is given, rather leads to misapprehen- 
sion. In our description, we shall use only two principal terms, which we regard as 
correlated to each other, namely, wmbilicus and columella. The first is either open, 
or covered with a callosity, the latter hollow or solid ; both in different degrees and 
varying in form requiring always special notice, not only in different species, but 
often even in certain specimens of the same species. 
