EISSOA. 377 



thium with some authors an unobserved animal, will, from 

 its paucispiral operculum, so similar to the present species, 

 probably, as a Rissoa, join its elongated dextrorsal comrade. 

 We have never se.en 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, pi. 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 " lo Paeans" with the illustrious author of 

 the ' Amorum/ since at last, as with him 



" Decidit in casses praeda 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 



