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Honjo to K?iow American Seashells 81
the last traces of flesh, the radula may be soaked in a saturated solution of
potassium hydroxide (KOH) for a few minutes. A solution of common lye
will do as well. Animals whose flesh has been hardened by a preservative will
have to be carefully boiled for a few minutes or soaked overnight in KOH
or lye. Small specimens may be dropped whole into this alkaline solution
if only the radula is desired. Transfer the radula successively to several
watch-glasses of clean water in order to rid it of all traces of KOH. The
radula may then be placed in one or two drops of water on a clean, glass
microscope slide and, by observation under the dissecting microscope, a few
teeth may be teased apart with fine needles. Leave some of the ribbon intact
to show the relative position of the teeth. Add a square cover slip for study
under the compound microscope. In w^ater mounts such as these, stains are
usually unnecessary. This temporary preparation may be permitted to dry
for a day, the cover slip gently lifted, a few drops of euporol or mounting
medium added, and the cover slip replaced to make a permanent shde. Some
workers prefer to go from water to eosin stain to ninety-six percent alcohol
and then to euporol, but this is an unnecessary elaboration. There are also
excellent, permanent, plastic mounting mediums on the market. Canada bal-
sam and glycerine jelly eventually deteriorate. Keep in mind that KOH or
lye will burn flesh and eat holes in clothing.
Pelecypod Features
Shape of shell. In most families of bivalves, the shape of the shell is
extremely important as a species character, and only in a few groups, such
as the oysters and mussels, is shape so variable within a species as to be of
little taxonomic value. Shape of shell, as a whole, is of little value in deter-
mining families or genera, except in a few instances such as Pecten, Spon-
dylus and Pinna.
Parts of the shell. The two valves of a clam are bound together by a
brown, chitinous ligament, and usually hooked together by a hinge which is
furnished with interlocking teeth. The valves are kept closed by powerful,
internal adductor muscles but kept spread open by the action of the ligament
when the animal relaxes or after it is dead. Each valve is a shallow,
hollov/ cone, with the apex, from which point growth of the valves commences,
turned to one side. This apex is termed the umbo (plural: umbos,
umbones) or beak. The hinge and its teeth are usually just below the beak
on the inside of the valve. The prodissoconch is the embryonic shell of the
bivalve, and corresponds to the protoconch or nucleus of the gastropods. It
is generally eroded away in adults, but when preserved it serves as a useful
identification character, especially in such groups as the oysters.
Right and left valves. It is important to distinguish one valve from the