78 CRETACEOUS GASTROPODA 
species of Lyra the plaits are not well developed, or in the fossil state not exactly 
to be observed, there is no possibility of distinguishing those shells from others, 
which are attributed to Turricula and other genera of the wrrrriv#. As to Fascio- 
laria and Volutilithes, the more elongated and narrow canal and the greater height 
of the spire of the former usually serve as more easily recognized differences. 
Looking to all the known cretaceous species of the rvozurivx we venture to say, 
that besides Volutilithes and Lyria, which are the most numerous, several other genera 
appear to be represented. In spite of the greatest and most marked resemblance in 
the exterior form of the shells, there is very often a smaller number of columellar 
plaits to be observed, as compared with the recent representatives. We can scarcely 
think that this character, which is so very much dependent on the good preserva- 
tion of the fossil, could be admitted as conclusive, although the difference ought 
always to be recorded. Several of the cretaceous species may form new generic types. 
We cannot, however, anticipate much success in an attempt to classify the known 
cretaceous species, in accordance with the present state of conchological science, 
because many of them are known only from very deficient specimens, and 
until this be remedied, the general term Voluta will often be most acceptable. At 
the same time we should not feel justified in reporting on such interesting material, 
belonging to the rozvriv#, as we have from the South Indian cretaceous rocks, 
did we not avail ourselves of the opportunity of showing, that such a division into 
more specified and restricted genera is not only necessary, but that the existence 
of such distinctions can be traced even in this remote period. We shall there- 
fore carry out this division in our special case, so far as it appears advisable. 
Deshayes, as usual, very much favours the unity of a ‘grand’ genus Voluta 
in Lamarck’s sense, although it is difficult to see with what advantage. It 
cannot be said to add to our detailed and specified knowledge, though no concholo- 
gist will deny, that all the numerous species described and known as Voluta belong to 
one group. The question will soon be reduced again to what authors may choose to 
call a genus, or a sub-family, family, or tribe. On page 583, M. Deshayes himself, after 
having discussed and established the unity of the genus Voluta, proposes five divi- 
sions or groups of this Volwta, and says they appear to be ‘useful,’ as we think no one 
will hesitate to admit. But if ‘useful,’ they must be definable by some character- 
istic distinction; and if this be once admitted, the desirability of a sub-division 
of Lamarck’s genus Voluta is abundantly established. Only the far less import- 
ant question will then remain, whether we prefer to eall such groups by a fixed and 
definite name, or to mark them by a letter a, 8, ¢, &e., and whether we carry the 
definition to a greater or lesser degree of strictness, for the convenience of further 
determinations. I believe it to be merely a matter of opinion and convenience, as 
to which of these systems tends most to our progress in the knowledge of different 
types of shells. I am of course well aware that many conchologists believe them- 
selves fully satisfied, that the genera in our zoological and botanical literature are 
and must be more than groups of necessary convenience, but it will soon be very 
difficult for them to find much support for these views. ‘That this—I mean mere 
