476 Mr. J. E. Gray on the Operculum 
I dedicate this species to M. Valenciennes, whose talents and 
associations with Lamarck and Cuvier place him im the first rank 
among our European scientific men. 
The only specimen known belongs to the Garden of Plants ; 
and in order to illustrate the distinctions between the three 
genera of this small family, I have given in Pl. XV. profile views 
of Magas (fig. 2), and Bouchardia (fig. 3), which thus express 
to the eye what the writer of this paper has been unable to 
describe. 
Fig. 1 is the natural size of Waltonia Valenciennesii ; the other 
figures are enlarged. 
I have also here to express my thanks to my old friend M. Bou- 
chard, to whom I exposed my views on this new genus, and in 
which he completely concurred. 
XLIII.—On the Operculum of Gasteropodous Mollusca, and an 
attempt to prove that it is homologous or identical with the second 
Valve of Conchifera. By J. E. Gray, Esq., F.R.S. 
To the Editors of the Annals of Natural History. 
GENTLEMEN, 
Havine for several years entertained the opinion that the oper- 
culum of Gasteropods is identical with the second valve of 
bivalve shells, and having in the ‘Synopsis’ of the British Mu- 
seum for 1842, and in several papers on Mollusca, mentioned 
it in that light, without any naturalist having attempted in 
any way to dispute the theory, I was mduced to believe that it 
had been adopted as an axiom ; but having lately mentioned the 
fact in the presence of Mr. Owen and several other comparative 
anatomists, and finding that they were not prepared to admit the 
propriety of the comparison, I have been induced to put on paper 
the reasons which led me to adopt the theory, which I have neg- 
lected to do before. I am the more induced to do so, as on reading 
Professor Lovén’s paper, I find that that very accurate and pro- 
found malacologist, who has paid much attention to the relation 
which the different classes of Moilusca bear to each other and 
the homologies of the different organs, though he has observed 
that these Mollusca are provided with a particular part, before 
very generally overlooked, which he calls the lobus operculigerus, 
but which I have long ago described as the mantle of the oper- 
culum, yet considers the operculum as analogous to byssus. His 
observations are as follows :— 
“The Gasteropods have also another part of the foot, which 
may be named /obus operculigerus, sometimes highly developed 
