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How to Knouo American Seashells 79
Beyond each lateral there is first an inner marginal and finally an outer mar-
ginal. This makes seven teeth in all. In the rachiglossate snails {Muricidae,
Buccinidae, Olividae, etc.) there are only three teeth per row—the rachidian
and a strongly cusped lateral on each side. The four toxoglossate families
(Conidae, Turridae, Terebridae and Cancellariidae) have lost their rachidians
and laterals and have retained only the marginals.
The docoglossate snails {Acmaeidae and Patellidae) have less than
twelve teeth per row but are peculiar in that there are two to four identical
rachidians or centrals. In the rhipidoglossate famihes {Trochidae, Fissurel-
lidae, Neritidae) the radula is very complicated, and the very numerous lat-
erals at the end of each row are called uncini. Among the gastropods which
do not have a radula are the Pyramidellidae, Eidijnidae, the genus Corallio-
phila, adult Harpa and a few genera of nudibranchs.
Figure 25. Types of radular teeth found in the prosobranch gastropods, a,
rhipidoglossate [Calliostoma doliarium Holten); b, taenioglossate (Littorina irro-
rata Say); c, rachiglossate {Purpura patida Linne); d, toxoglossate {Comis clarki
Rehder and Abbott); e, reduced rachiglossate {Scaphella jiinonia Shaw). All
greatly magnified and representing only a single transverse row of teeth.
We have figured several main types of gastropod radulae (fig. 25), but
other examples have been included in the systematic section when they are
of especial use in identification. It is not expected that many amateurs will
want to prepare and examine radulae but, because so many serious private
collectors and many biology students will find this identification tool indis-
pensable, we have included brief instructions on the preparation of radula
slides.
Preparation of the radida. In large specimens, such as the whelks or
conchs, the proboscis may be slit open from above and the round buccal
mass removed. Occasionally, the proboscis is withdrawn far inside the ani-
mal, but it is easily located below the thin skin on the dorsum just posterior
to the tentacles. The flesh may be torn away with the aid of small dissecting
needles until the glistening, worm-like radula pops out. In order to remove