OF SOUTHERN INDIA. 548 
The shell is spiral, turbinate or depressed, and generally pearly within. The 
operculum is spiral, horny, or to a larger or smaller extent calcareous. 
The CILIIPEDATA contain such a large number of different shells, that it appears 
most desirable to divide them into several families. Many conchologists object to 
these family-divisions on the ground that the characters of distinctions are not equal 
in importance to those upon which other families of Gastropoda are generally 
formed. It seems to me, however, that these objections are more due to the want 
of our present knowledge of the animals, than to any real identity in organisation. 
The distinctions of the Trocuipm and Tursinip# are certainly not very important, 
still they are remarkably constant. The animals of the Lzorzp# are as yet very 
little known. The less pearly internal structure of the shell and the peculiarly 
formed operculum makes it very probable that some remarkable distinctions exist in 
the animals. The little reliable information which we have of the animal of 
Umbonium seems to show that the family Umsonmpa (Rorrrzii2z) is fully entitled 
to that distinction. We shall in our divisions of the families principally follow. the 
classification of Dr. Gray, in his Guide of 1857. 
In geological history the CinimEpAta belong to the number of the oldest 
known Gastropoda, for they appear to be represented even in the lower Silurian 
rocks. It is true that some of them have a form common to many Lzrrorrvipz 
or Sozariups#, and thus can very easily be mistaken for genera belonging to those 
families; still there are many others of such characteristic and typical forms as 
leave little doubt regarding their correct determination. During the secondary 
epoch the species of the CImLIrPEDATA increase very largely in number, and many 
genera are met with which are at the present time still to be found in tropical seas, 
though very rarely. The tertiary deposits are equally rich as regards number of species, 
but these, as likewise those of the secondary epoch, generally are of small size, while 
the recent fauna is characterized by very many species of large size. As to the 
number of generic types the present fauna may be considered the richest, though a 
large number of the genera were already represented in former periods. Still many 
additions can justly be expected, when dredging operations have been extended to the 
different tropical seas, for there are found exactly those minute forms which are so 
common in a fossil state, and of which so many new generic varieties have been 
added to our knowledge during the last few years. Almost every conchological 
excursion may be said to furnish quite new materials in this tribe of Gastropoda. 
Asarule, the larger number of the C1LItpEDATA are littoral inhabitants, feeding 
on sea weeds; they are also common on coral reefs, and are much more numerous 
in the eastern than in the western seas. We accept here the following families,— 
L.—UOMBONTIDZ, 
LI.—LIOTHD 2, 
LIL—TURBINIDZ, (Sub-fam, PHASIANELLINE, TURBININE, and ASTRALIINZE), 
LIII.—_ TROCHIDA, (Sub-Sam. GrepuLin#, TROCHINE, MARGARITINE and DELPHINULIN 2). 
LIV.—_STOWUATIID 2, 
the last of which forms a passage to the Hazroripa. 
