South of Italy, and more particularly of Sicily, 211 
are most abundant at the present day, such as, Venus geo- 
graphica, Venus laeta, Poli, Turbo neritoides, L., did not 
exist during the Tertiary period. 
It may be asserted, generally, that the differences observed 
between living and fossil specimens of the same species, are 
not greater than those which occur between individuals of 
the same species ; nay, it is not at all a rare occurrence, to 
find difficulty in determining whether a specimen be fossil or 
not. This is the case, for instance, with the specimens oc- 
curring in the clay of Abbate, near Palermo, which are washed 
out by the sea, and are very often inhabited by hermit-crabs. 
These species are frequently in an astonishing state of preser- 
vation ; and hence there is a sufficient apology for their being 
regarded as recent shells. This seems to have taken place 
with those conchologists, who, like Linnzeus, assigned Sicily 
asa locality to Dentaliwm elephantinum ; and also with Kiener, 
when he included Murex vaginatus among the living species ; 
but, in the latter instance, the author is very much to be 
blamed for altering the names. 
It is, however, remarkable that certain species seem to have 
been very much larger in former times than they are at present, 
We have striking examples of this fact in Lucina radula, 
Lucina fragilis, Cytherea rudis, Poli, Venus radiata, Car- 
dium Deshayesii, Cardium papillosum, Mytilus edulis, Pileop- 
sis wngarica, Turritella communis, and Turritella triplicata. 
I could enlarge this list considerably; but still the ma- 
jority of the species agree completely in size; and, what 
is very singular, certain species were constantly much smaller 
during the Tertiary period than they are at present ; the num- 
ber of the latter, however, is comparatively small. As ex- 
amples of this circumstance, I would particularly instance 
Bulla lignaria, and Terebratula vitrea, which formerly scarcely 
attained half the size they now present; and, next to them, 
I would mention Corbula nucleus.* 
From these facts nothing further can be deduced than that 
* In my Enumeratio molluscorum NSiciliw, I have invariably given the 
relative sizes of the fossil and living shells, when they differed from each 
other. 
