REMARKS, xi 
Changes made on one side proved the necessity for others, and it was scen 
that by no better and more accurate means could the correct comparison of the 
former with the present physical conditions be tested than by the study of the 
organic life, and specially of that of the Mollusca. It was then necessary to go into a 
closer comparison of the fossil* forms with the living ones, and to make use of the 
considerable systematic progress which had been attained in recent Conchology 
principally through anatomical researches. 
The great disadvantage in studying fossil forms is, that direct observation as 
to the connections existing between the animal and its shell are to a great extent still 
in their infancy. It is most important to know which particular secretion on the 
aperture corresponds to a certain organ, and in what connection this latter stands to 
the total organism; whether its changes are essential and necessarily dependent 
upon others in the organisation of the animal, or whether they may be produced by, 
and can therefore be attributed to, local and accidental causes only. Wecan hardly 
expect, that our fossil genera will have an unquestionably firm basis, until these 
morphological and anatomical studies have been very considerably advanced. It is, 
however, by no means intended to say that our present knowledge of the anatomy 
of the animals is so totally deficient, that we cannot form any certain conclusions 
from the structure of the shell to that of the animal. We do not need to enumerate 
the many most valuable results, which have been already obtained from those studies 
in fossil Conchology. 
But the more we enter into a detailed examination of local faunse, the more 
urgent appears the necessity for reducing to some extent the old established ‘ grand’ 
generic groups, and for adopting instead the smaller and more easily defineable genera, 
which have been established by the more rapid progress of recent Conchology. 
I hardly need to repeat, that our studies, both systematical, as well as physical 
and geographical, are most remarkably simplified by the adoption of this course. 
That we shall have to struggle, for some time to come, with the number, limit and 
definition of those genera is an undoubted fact, but this does not in the least 
invalidate the principle, which ought to be adopted. It is most probable, for 
instance, that a large proportion of the genera and sub-genera, introduced by 
H. and A. Adams in their ‘Genera’ will prove to be quite unnecessary, others 
will be differently determined, and many more are constantly proposed. But when 
all the recent shells have been thus carefully examined, several of our, as at present 
believed, fossil genera will be shown to have still living representatives, and others, 
which have really disappeared altogether, will be entered into the system according to 
* I mean to refer here principally to the meso-and palzeo-zoie fossils. 
