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XXV. On Fossil Shells. By Lewis Weston Dillwyn, Esq. 
F.R.S. In a Letter addressed to the Right Honour able Sir 
Humphry Davy, Bart. Pres. R. S. 
Read June 5, 1823. 
My Dear Sir, 
A s fossil shells are more numerous, and generally occur 
in a better state of preservation than any other of the organic 
remains, they have become one of the most interesting ob- 
jects for geological research, and there is such an exact 
conformity in the structure of many of these fossils with the 
living genera, as to render it in the highest degree probable, 
that the habits of their animals were also similar. By availing 
ourselves of these analogies, some circumstances attending 
the distribution of fossil shells may be observed which have 
hitherto escaped notice, and if you should find them to be 
sufficiently interesting, or likely to open a new door for 
enquiry, I beg that you will submit to the Royal Society the 
following observations on the fossil remains of the Molluscse. 
Pliny, in describing the shell fish which was supposed to 
yield the Tyrian die, has observed, ‘ lingua purpuras longitu- 
dine digitali, qua pascitur perforando reliqua conchylia and 
Lamarck says, that all those molluscse whose shells have a 
notch or canal at the base of their apertures, are furnished 
with similar powers, by means of a retractile proboscis ; and 
in his arrangement of invertebral animals they form a sec- 
tion of the Trachelipodes, with the name of ‘ Zoophages/ 
Whether all these Trachelipodes are possessed of the same 
predaceous powers of boring into hard substances, and whe- 
MDCCCXXIII. 3 E 
