> It seems Swainson erected the genus-group Thelidomus twice - and in the same
> work (1840: 191-192, 330 and 228, 353)! On page 330 the type species of the
> usage which appeared in p. 191 is given as Helix striolata Guilding, a
> synonym of H. incerta Férussac, 1821 according to Pilsbry (1894: 97), an
> Antillean camaenid land snail. The second usage appears on p. 228 with text
> figure depicting a typical Helicopsyche "shell" but with no associated
> species group name of any kind. On p. 353 the name Thelidomus reappears
> again with the juxtaposed text figure, but this time with "Braziliensis Sw."
> appears in the caption.
>
> I suspect the "First Reviser" who saw the homonymy selected the camaenid as
> the senior homonym based on "position priority" (page number 330 vs 353), an
> attribute which no longer mandates seniority.

That seems likely, but I haven't chased down first reviser on this.
It can be a very difficult process-there's always the chance that some
overlooked publication has gotten in first.

Identifying Swainson types is very messy.  As noted above, he didn't
seem to have the greatest proofreading, such that the same thing
sometimes has more than one name or the same name gets used more than
once.  Furthermore, he had a convoluted idea that patterns repeated
themselves across taxa and across taxonomic levels.  Thus, there were
parallels between bivalve taxa and gastropod taxa, parallels between
members of one family and another, parallels between species in a
genus and the closely related genera, etc.  He also did not think of
genera as having a unique type.  Often one species is singled out for
special attention, but more than one species may be called a "type",
and in at least one case he calls a species the "type" of genus X when
he means that it belongs to genus Y but represents the genus X-like
parallel within genus Y.  Unless he mentions a single species in the
genus (or in at least one case, two different species names for the
same specimen), thus accidentally identifying the type by monotypy,
almost all of his genera depend on subsequent designation.  Gray
(1847) and Herrmannsen (1847 and later) are two of the earliest
revisors who cite types for Swainson.  It doesn't help that Swainson
sometimes cites the author who figured a species rather than the
original author of a species.

For example, what's Potomida Swainson?  Swainson's main example was a
synonym of littoralis, a European and circum-Mediterranean unionid
bivalve.  However, he also cited sinuatus, a synonym of auricularia, a
European margaritiferid, as typical of Potomida.  Potomida is
frequently used as the genus for littoralis.  However, first Gray and
then Herrmannsen designated sinuatus as the type.  It would be the
oldest genus name based on either species.  As far as I can tell,
legally Potomida should be the margaritiferid, but it has received
rather more use for the unionid.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

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