948 SUPPLEMENT 
cinum Japillus, the neritina of the rivers, the common patella, 
the eatable oyster, the eatable mussel, and many species of 
cardia, &c., in whom we find individuals in the same locality 
differing one from the other, in all those characters of the 
shell which we have enumerated above. 
More justly may we conceive that an assemblage of cir- 
cumstances to a certain point inexplicable, and which have 
acted for a very long period, may have influenced almost in a 
fixed manner a succession of individuals of the same species, 
and determined in shells certain differences in size, propor- 
tion, colours, system of coloration, and even in the state of 
the superficies, smooth or rugose, especially when they shall 
be compared to other individuals of the same species living 
for a long series of ages in different localities. These differ- 
ences then really constitute, as it would appear, but simple 
fixed varieties, so much the more dissimilar as the localities 
are more remote, and which we may, if we think proper, de- 
corate with the name of local species, but which are not real 
species. In fact, when we come to assemble these pretended 
species from a great number of different localities, we shall 
find that they pass one into another in a manner almost in- 
sensible. M. Defrance, who had occasion to make the same 
remarks on the distinction of fossil shells, inquires whether a 
species be genuine if that to which it approaches the nearest 
is to be found in the same locality? Though this rule can 
hardly yet be considered as very rigorous, it may assist in a 
subject so difficult, and one so important for geology. ‘The 
minute study of living species can alone furnish analogical 
means to diminish the difficulty, and consequently supply 
geologists with data, to resolve the problems concerning the 
analogy of formations in the structure of secondary and ter- 
tiary strata. 
Notwithstanding the great length to which this supplement 
on the division has already extended, we can find no better 
