200 Shell Life 



its shell the operculum comes last and accurately 

 closes the mouth of the shell. In some species this 

 operculum is composed of hard shell material, but in 

 the Dolphin-shells it is horny and of spiral structure. 

 The Shining Dolphin - shell (C. nitens) is thin, 

 white, glossy, and slightly iridescent, Avith three 

 whorls and a thickened lip. The animal has a 

 bilobed snout, thread-like tentacles from the head, 

 and tentacle-like appendages to the foot — three or 

 four on each side. It is found in the coralline zone 

 on the coasts of Devon, Cornwall, Guernsey, all 

 round Ireland, and the west of Scotland. The other 

 species is the Flat Dolphin-shell (C. serpuloides). 

 The specific name of this mollusk was bestowed 

 because the shell was thought to resemble the shelly 

 tunnel of the Tube-worm {Serpida). It is almost flat, 

 the spire being scarcely raised. It occurs between 

 low water and a depth of 25 fathoms on all our 

 coasts. It is thought by some that the species 

 described below as Trochiis clmninyi should come 

 here under the name of Circidtis striahis, but as 

 the shell alone is known we think it best to retain 

 it provisionally where Jefi'reys placed it, as the 

 discovery of the animal will almost certainly lead 

 to other arrangements. 



The Top-shells {Trochiis) are closely related to the 

 Dolphin-shells, as will be evident on comparing the 

 animals with their ciliated tentacles and side 

 appendages, although system atists have placed 

 them in separate families. These differ from the 

 last in the shells always having a layer of pearl 

 beneath the outer coat of shell material, and in the 

 mouth of the shell being oblique and somewhat 



