96 JOURNAL, BOMBA Y NATURAL HISTORY SOCIETY, Vol. XVIII. 



(4) Posterior retractor impression. — Small and continuous with the upper 



and anterior edge of adductor impression. 



(5) The Pallial line is the line of attachment of the mantle to the shell 



running almost parallel to the ventral edge of the shell. 

 Structure of Shell. 



(1) An outer coloured " Periostracum " or skin. 



(2) A middle or prismatic layer which is densely calcified. 



(3) An inner nacreous or pearly layer often highly iridescent. 



The following shells are the more common kinds the collector is most likely 

 to meet with, and the descriptions and measurements are taken from specimens 

 in my own collection. All measurements are in millimetres and must only be 

 regarded as approximate, though I have taken especial pains to select only 

 adult specimens. 



GASTEROPODA. 



Neritid^e. 

 Neritina perotetiana (Recluz). 

 Shell. — Thick with very small spire. Operculum shelly. Underside ex- 

 panded and flattened above the mouth. 



Colour. — Above dark brown to black. Flattened portion whitish. 

 Length. — 11. Hill streams in the Nilgiris. 



VlVIPARID^E. 



Vivipara bengalensis (Lmk). 



Shell. — Conical. Whorls five. Operculum shelly. 



Colour.— Greenish banded very strikingly with reddish brown. 



Length. — 35. 



This i3 an exceedingly common shell, especially so in Bengal, being found in 

 all rivers and marshes. All the Viviparidce, as the name implies, are vivi- 

 parous and the young shells have* rows of epidermal cirri. 



V. dissintilis (Mull). 



Shell. — Conical, operculum thick and horny. Whorls 4. 



Colour. — Green when clean but often eroded with a slimy growth. Some 

 specimens I have are of a clear amber colour, but this may be due to decay as 

 they were all picked up dead. 



Length. — 20. Found in same situations as the last. 



V. prcemorsa (Bens). 



Shell. — Conical. Whorls 4-5. Operculum thick and horny. 



Colour, — A uniform olive-yellow. A brown thin line round the lip. Marked 

 with faint line chiefly on underside. 



Length. — 25. 



V. ceylanica (Dohrn). 



Shell. — Conical. Lip acute. Whorls 5. Operculum very thick. 



Colour. — A uniform reddish yellow. Lip black. 



Length.— 28. Island of Ceylon. Common. 



