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 in 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 PI. XV. profile views 

 of Magas (fig. 2), and Bouchaj'dia (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 Molluscaj 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, 



Having 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 induced to beheve 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 Loven^s paper, I find that that very accurate and pro- 

 found malacologist, who has paid much attention to the relation 

 which the diff'erent classes of Mollusca 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 lobus operculigerus y sometimes highly developed 



