TLTvBO. 145 



form; with the tentacles a little behind,, the eyes are upheld 

 on short pedicles at the outer base^ and the disc is short 

 and thick, with mostly a calcareous, although occasionally 

 a horny, operculum. 



The shells, however, of these genera afford distinctive 

 characters, sufficiently prominent to entitle them to be dis- 

 tinguished in the manner generally adopted ; and although 

 the opercula furnish no data for generic arrangement, 

 their varieties are extremely interesting. Those small doors, 

 on which much of the comfort and well-being of the 

 possessors depend, are mostly of a solid testaceous sub- 

 stance, but either smooth or granulous, deeply and cir- 

 cularly grooved with ridges, granulated or serrated, or else 

 composed of club-shaped particles, forming a kind of tuft. 

 An exception with regard to their solid testaceous substance 

 occui's in the T. pica, and one or two other species : in these 

 the operculum consists merely of a horny lamina, without 

 any calcareous deposit. 



Nor less curious and varied are the shells of the genus 

 Turbo ; occasionally smooth, and almost porcellaneous, but 

 mostly ribbed or grooved, and ornamented with scales or 

 laminae. The interior layer and chief substance of the shell 

 consists of mother-of-pearl, often iridescent, sometiuies 



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