xii INTRODUCTORY 
their respective relations. The recent fauna is only a remnant of that which existed 
during the previous periods of life on our globe, and its uniform plan of organization 
is sufficient proof that, strictly speaking, the present fauna marks only a certain 
stage in the entire progressive development of organic life.* Unless, however, i 
am very much mistaken in the meaning of the term of a natural system, (which I 
believe ought to be the exposition of this gradual development of organic life), 1 am 
entirely at a loss to perceive, how conchologists can expect to arrive at a natural 
system from and through the examination of the recent species alone ! 
Were it certain that there are in reality no extinct, new, or differently typical, 
forms of Mollusca known, no such objection could be very reasonably raised; but 
as the reverse is to the extent of our present knowledge an undoubted fact, the con- 
chologist must look upon a purely zoological system only as a partial systematical 
arrangement, or an incomplete attempt at a natural system. 
Perhaps the system now adopted, which has become so highly favoured among 
a number of conchologists, might well be called hyper-anatomical. It sounds 
almost like a dream to hear of the grand results, which are expected to be derived 
from the examination of the dentition of a few species, when Mr. Moérch says, that 
‘«a, monographic research, chiefly based on the teeth of the genera Nassa, Fusus and 
Buccinum, found on the coast lines from the arctic regions to the equator, would 
probably be sufficient to prove, whether species in each fauna are created originally, 
or are only varieties dependent on different climates, and would at the same time 
prove the relations between the species of succeeding geological periods.” Where, 
whether, and how all these inquiries of the past and the present are inscribed on 
the teeth of the Mollusca will probably not be easy to find out. This seems to me 
a similarly exaggerated idea, as if some palzeontologist would attempt to obliterate a 
carefully obtained zoological result through the examination of a few imperfect 
shells, for such they are in the largest number of cases in our fossil Conchology. It 
is only by the co-operation of both the zoologist and paleontologist (although the 
latter will always gladly give the lion’s share to the former), that a true natural 
system of Conchology can be obtained. 
For some time I entertained the project of collecting all the different types 
of Mollusca, and specially of the Gastropopa, from the oldest to the more 
recent formations, and thus being in possession of a series of types for comparison 
-with the living shells. A task like this is, however, not easily executed, for the 
* When certain highly organized forms are placed under the influence of conditions of life so different, 
that their organs lose something of their inherited development, instead of becoming more highly specialized, 
this case of so-called retrograde metamurphosis can scarcely be looked upon as anything more, than an excep- 
tional case, inasmuch as it does not interrupt the general tendency to progression. 
