THE / 



JOURNAL ^_ 



OF THE 



Natural History Society of Slam. 



Volume IV. BANGKOK. Number 1. 



THE APPLE-SNAILS OF SIAM. 



By N. Annandale, D. So., F.A.S.B., 



(Zoological Survey of India). 



With 2 plates. 



The Ampullariidae or Apple-Snails are the largest of the 

 freshwater Gastropod molluscs and can as a rule be recognized by 

 their comparatively great size and by their almost globular shells. 

 Even the smaller forms are considerably larger than most other 

 water-snails, but a few gigantic Pond-Snails (Viviparidae), found 

 mostly in China, are larger than the smallest species, and approach 

 the Ampullariidae in shape of shell. The Oriental Apple- 

 Snails can, however, be readily distinguished from all others of 

 large or moderate size found with them by their thick shelly 

 opercula, and by the fact that they possess, in addition to the ordi- 

 nary tentacles, a tentacle-like process on either side of the mouth. 

 They are found in ponds, marshes, rice-fields and sluggish streams, 

 where aquatic vegetation grows luxuriantly, for they are voracious 

 feeders and their chief food consists of water-plants, which they 

 masticate by means of a pair of stout horny jaws, situated laterally, 

 as well as scraping them with the teeth of their lingual ribbon, which 

 are unusually large. On occasion they will eat decaying animal 

 matter, including the bodies of their own kind, and some species 

 rasp small algae from the shells of their fellows, causing unsightly 

 patches as they remove the epidermis or periostracum with the algae. 



