MANUAL OF NATURAL HISTORY. 135 



46. FAMILY. Sargasso, - Shells (Litiopidse). Eyes 



sessile on outer bases of tentacles ; mantle 

 with a siphon in front ; foot with tentacular 

 filaments on the sides ; operculum sub-spiral; 

 shell sub-turreted ; aperture with a distinct 

 notch in front. Marine. 



47. FAMILY. Salt-Water Clubs (Cerithiidge). Eyes 



on outer sides of tentacles ; mantle with a 

 siphonal fold or a distinct siphon in front ; 

 operculum ovate, sub-spiral ; outer lateral 

 teeth conical, curved ; shell turreted ; aper- 

 ture more or less beaked and channelled in 

 front ; outer lip expanded. Marine. 



48. FAMILY. Fresh-water Clubs. (Melaniidse). 



Eyes sessile on outer bases of tentacles ; 

 mantle margin fringed, with a slight siphonal 

 fold in front ; operculum sub-spiral ; lateral 

 teeth multicuspid ; shell spiral, many-whorl- 

 ed, covered with an epidermis ; aperture 

 usually simple in front. Fluviatile. 



49. FAMILY. Screw-Shells (Turritellidse). Tongue 



very short, minute ; eyes on bulgings at 

 outer bases of tentacles; mantle - margin 

 fringed, nearly entire in front ; a single long 

 branchial plume ; operculum circular, mul- 

 tispiral, edges of whorls fimbriated ; shell 

 turreted, many-whorled ; aperture simple 

 in front. Marine. 



50. FAMILY. Rissoellas (Rissoellidse). Eyes sessile, 



far back behind tentacles ; rostrum bifid, 

 lobes nearly as long as tentacles ; opercu- 



