102 UNIVALVES. 



during the formation of its shell, collects these 

 various substances ; probably some very tena- 

 cious matter is combined with its calcareous 

 secretions, which cause whatever comes in con- 

 tact with it before it is hardened, to adhere to its 

 surface. 



GENUS TURBO.* 



TURBAN-SHELL. 



Generic character. Shell univalve, spirally 

 convoluted, solid ; shape more or less conical ; 

 aperture entire, contracted, orbicular. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The shells of this and the preceding genus 

 are often so similar, that it is difficult to define 

 the boundaries by which they are separated ; the 

 mouths of the Trochi gradually losing the an- 

 gular, and assuming the orbicular form ; whilst 

 many species of the Turbines exhibit a very im- 

 perfectly circular aperture. The names of both 

 these genera imply any thing that whirls round ; 

 they both exhibit a conical form, and are also 

 nearly allied in habits, as well as in appearance. 

 The marine species are found on rocks and 



* Plate IV. figures 7, 8. 



