RISSOA. 377 
thium with some authors—an unobserved animal, will, from 
its paucispiral operculum, so similar to the present species, 
probably, as a Rissoa, jom its elongated dextrorsal comrade. 
We have never seen it alive, but it ought to be observed, as 
it is not very uncommon on the Plymouth and Cornish coasts. 
With respect to the shell called Cerithium metula, it is 
transferred, ad interim, as a congener of Murex tubercularis. 
R. unica, nobis. 
Aclis unica, Brit. Moll. iii. p. 222, pl. 90. f.4, 5. 
Chemnitzia unica, Alder et nobis. 
Turritella unica, Fleming. 
Turbo unicus, Mont. et Auct. 
Exmouth, 29th June, 1854. 
I now give an account of a very rare mollusk which I 
discovered this day, and which has hitherto evaded, in a living 
state, all our researches; I have sought it for thirty years, and 
may therefore sing “Io Pzeans”’ with the illustrious author of 
the ‘Amorum,’ since at last, as with him— 
** Decidit in casses preeda petita meos.” 
Let this instance of unexpected success impress on us the 
value of the “nil desperandum.” The discovery of this crea- 
ture has long been a desideratum, as it will solve several 
malacological questions: it has from Montagu’s time run the 
gauntlet of nearly all the genera, agreeably to the concholo- 
gical surmises of naturalists, of whom scarcely ‘two are in 
accord, and all in error; as my notes require me to place it 
in a position it has never yet occupied, and which, I believe, 
will prove to be its true malacological status. Our ignorance 
of every circumstance attendant on this almost microscopic 
being has invested it with a strange diversity of position and 
consequent structure ; but the light of discovery that now 
dawns on us will dissipate, as in every case, misapprehen- 
sions, and tell us the Fates have decreed, that we all should 
be at fault about a very simple creature, which, though not 
absolutely a typical Rissoa, is all but one, as the shell only 
wants the callus on the outer lip; but we have many admitted 
