2 32 Shell Life 



mollnsk has the faculty for spinning invisible threads, 

 and by this means suspending itself from the weeds 

 or from the surface of the water. It is impossible 

 here to give descriptions of the numerous species, 

 whose names will be found in the list at the end of 

 the work. 



The Red Spire-shell {Barleeia rithra) is distinct 

 from the Rissoce only in that the opercular lobe is 

 without appendages and the operculum more solid. 

 The genus Hydrohia, too, is but little removed from 

 Rissoa, and less so from Barleeia, with which it 

 agrees in the absence of tails to the operculum lobe. 

 The shells are smooth, and just beyond the mouth 

 there is a cliink which appears like the 

 approach to an umbilicus. We have four 

 species, of which one, the Laver Spire-shell 

 {H. idvce), is partially marine. It feeds in 

 great numbers on the Laver or Sea Lettuce 

 {Ulva latissmia), whether this be between 

 tide-marks on the seashore, in rock-pools, or in 

 estuaries, and as far up tidal rivers as the salt water 

 extends. The other species (H. shnilis, H. ventrosa, 

 H. jenJdnsii) have taken themselves up the rivers 

 where the fresh water greatly predominates over the 

 salt, H. siviilis being found in the muddy ditches of 

 the Thames marshes between Greenwich and Wool- 

 wich, where it has for company so distinctly fresh- 

 water a form as Bithynia tentaculata and the more 

 marine Asshninia gray ana. In the small genus 

 Jeffreysia the minute shells are thin and glossy, 

 and the operculum has a slight projection from 

 the straight inner side. /. diaphana occurs on 

 Delesseria and other seaweeds at low water ; ./. 



