On 06/23/99 17:22:46 you wrote:
>
Are modern
>Busycon shells more brittle than those of other large gastropods?

There is a number of modern mollusks species which are actually more brittle than others and
Busycon might be one of those. Below, comments based on field observations...
There is the question of aragonite/calcite proportion  deposited in the shells as well as there
are taphonomic processes involved in this issue.
In fossil and sub-fossil beach deposits of western South America the gastropods Malea ringens,
Cassis centiquadrata and the bivalves Raeta undulata, Lima pacifica, Ostrea spp, and
Choromytilus chorus are among the large species which are seldom found as complete specimens,
regardless of their  origin whether from in situ or storm deposits.  Their shells are also "more
calcitic" in terms of the greater proportion of calcite vs aragonite crystals in their
composition.
They are usually in broken, angulose pieces except when found in modern low energy environments.
They're mostly absent from their related mollusk assemblages when in fossil and/or subfossil
deposits.
This attribute of shell preservation could be an important issue when dealing with
paleocological interpretations: the absence of any of these from their related mollusk
assemblages does not necessarily imply they did not exist in such locality, but rather that
these might be, in the area, the most fragile shells in terms of breakage and/ or dissolution.
For example, small, poorly preserved beak  fragments of the large blue mytilid Ch. chorus have
been "exceptionally" found in deposits of Holocene age and is almost absent from most of its
related assemblages at older deposits, Early to Late Pleistocene.  The greater calcite
proportion in their shells has been related to a lesser calcium carbonate stability during the
process of fossilization.  Thus,  mollusks which are more calcitic than aragonitic in their
shell composition are not found at certain shell beds because the can not be well preserved.