GASTEKOPODA. 239 



Distribution, 111 species. West Indies, Mauritius, Australia. 

 Fossil, 12 species. Chalk — . France, Britain. 



Odostomia, Pleming, 1824. 



Etymology, odous, a tooth, and stoma, mouth. 



Tijpe, 0. plicata. PL YIII., Fig. 12. 



Shell subulate or oyate, smooth; apex sinistral; aperture 

 ovate ; peristome not continuous ; columella with a single 

 tooth-like fold; lip thin; operculum horny, indented on the 

 inner side. 



Distribution, ? species. Britain, Mediterranean, Eed Sea, 

 Australia. 



Fossil, 15 species ? Eocene — . Britain, Prance. 



Very minute and smooth shells, having the habit of rissoce, 

 and like them sometimes found in brackish "water. They range 

 from low water to 40 fathoms. The animal is undistinguishablo 

 from chemnitzia. 



Chealnitzia, D'Orbigny. 



Etymology, named in honour of Chemnitz, a distinguished 

 conchologist of Nuremburg, who published seven volumes in 

 continuation of Martini's " Conchylien-cabinet,^' 1780-95. 



Synonyms, Turbonilla, Eisso. Parthenia, Lowe. Pyramis and 

 Jaminea, Br. Monoptigma, Lea, part. Amoura, Moller. 



Type, C. elegantissima. PI. VIIL, Pig. 13. 



Shell slender, elongated, many-whorled ; whorls plaited ; 

 apex sinistral ; aperture simple ; ovate ; peristome incomplete ; 

 operculum horny, sub-spiral. 



Animal head very short, furnished with a long, retractile 

 proboscis; tentacles triangular; eyes immersed at the inner 

 angles of the tentacles ; foot truncated in front, with a distinct 

 mentum. 



Distribution, 32 species. Britain (4 species), Norway, Medi- 

 terranean. Probably world-wide. Eange from low water to 

 90 fathoms. 



Fossil, 240 species. Silurian — . Britain, Prance, &c. 



The "melanise" of the secondary rocks are provisionally 

 referred to this genus. Those of the palaeozoic strata to 

 loxonema. 



Sub-genera. Eulimella, Forbes. E. scillae, Scacchi. 4 British 

 epecies. Shell smooth and polished ; columella simple ; apex 

 sinistral. 



Stylojpsis (xidams, 1860) much resembles and is probably 

 synonymous with this sub-genus. 



