and Observations on Shell and Bo 7 ie. 319 
became less, so that the disengagement of the carbonic acid gas 
was to be perceived only at intervals. 
At the end of two days, I found nearly the whole of the car- 
bonate of lime dissolved ; but a series of membranes, retaining 
the figure of the shell, remained, of which the epidermis consti- 
tuted the first. 
In the beginning, the carbonate of lime was readily dissolved, 
because the acid menstruum had an easy access ; but, after this, 
it had more difficulty to insinuate itself between the different 
membranes, and of course the solution of the carbonate of lime 
was slower. 
During the solution, the carbonic acid gas was entangled, 
and retained in many places between the membranes, so as to 
give to the whole a cellular appearance. 
The Haliotis Iris, and the Turbo olearius, resembled this muscle, 
excepting that their membranaceous parts were more compact 
and dense. 
These shells, when deprived by an acid menstruum of their 
hardening substance, or carbonate of lime, appear to be formed 
of various membranes, applied stratum super stratum. 
Each membrane has a corresponding coat or crust of car- 
bonate of lime ; which is so situated, that it is always between 
every two membranes, beginning with the epidermis, and end- 
ing with the last formed internal membrane. 
The animals which inhabit these stratified shells, increase 
their habitation by the addition of a stratum of carbonate of 
lime, secured by a new membrane; and, as every additional 
stratum exceeds in extent that which was previously formed, 
the shell becomes stronger in proportion as it is enlarged; 
Tt 2 
