QQ INTRODUCTION TO CONCHOLOGY. 



Other contrivances are obvious^ in different kinds of mol- 

 lusks. The Bulimus decoUatus, and many species of Pupa, 

 allow the early portion of their shells to fall away, — a poet 

 perhaps wonld tell you, for the pleasure of roofing over the 

 whorls by new concentric layers ; and doubtless the creatures 

 take much delight in varying and adorning the fairy-like 

 domes in wliich they dwell. Why else does the Magilits, that 

 singular tenant of the coral rock, fill up the deserted portion 

 of his shell with testaceous matter ; or the Coiory adorn his 

 dome-shaped dwelling with the most exquisite embellish- 

 ments ? 



An additional muscle further belongs to such species as 

 possess an operculum, for the purpose of drawing that ap-. 

 pendage within the aperture. The operculum is a shelly or 

 horny plate, adapted in most species to answer the purpose 

 of a door, by closing tlie aperture of the shell ; occasionall}^, 

 however, it is merely a small, thin, horny plate, of which the 

 object is unknown. 



A low degree of sensibility belongs, apparently, to all 

 Gastropods. Some species are even capable of reproducing 

 any member, when accidentally destroyed. Some, also, re- 

 main torpid for a great length of time ; and an instance is 

 recorded in the ' Elements of Conchology ' of some Helices 



