io8 



MADRAS FISHERIES BULLETIN 



VOL. XIV, 



Owing to this high specialization it is difficult to arrange their 

 relationship in any comprehensible sequence ; one can form groups 

 easily seen to have mutual affinities, but these groups stand apart 

 from others, and it is practically impossible to arrange them in any 

 satisfactory order that will show the line of descent or of 

 specialization. They represent the terminal twigs of a great 

 branch, and while they acknowledge a common ancestry, they 

 stand to each other as cousins of varying degree. 



If we follow the classification of Pelseneer, perhaps the greatest 

 of living authorities upon the mollusca, we take first two families 

 living in fresh-water, the Viviparidae and the AmpuUaridae. The 

 former is represented in India by the common fresh-water snail, 

 Vivipara, so called because it is viviparous — the young develop 

 within the parent and are born as tiny miniatures of the adult and 

 ready at once to begin life independently. The shells are thin and 

 comparatively fragile, covered with a thick olive-green periostra- 

 cum ; the shape is like a Turbo — hence this form of shell is said to 

 be turbinate, coiled like a turban. It lives in tanks and streams 

 and is occasionally eaten by low-caste people in the Southern 

 Tamil districts where it is known as uinachchi. 



Even more common is the larger APPLE-Snail, Pachylabra 



carinata, formerly known as AnipuUaria glohosa {naththai, Tamil), It 



^ grows to a comparatively great 



size, and may even exceed one and 

 a half inch in diameter. The shell 

 is nearly globular with a small 

 spire and a very large mouth open- 

 ing. In appearance it is like a big 

 globular Vivipara ; the two are 

 often found together in ponds and 

 paddy fields, but Pachylabra 

 appears to be the more hardy, for it 

 has the advantage over Vivipara of 

 having an air-breathing organ or 

 rudimentary lung, in addition to a 

 gill for use under water. This 

 enables it to live in comfort for some time even out of water 

 and so to withstand successfully the vicissitudes of a tropical 

 country. It can also lie hidden in soft mud and still obtain air by 





Mm 



' 



'm 



mm 



if::/'(t; 



Fig. 



Apple-Snail {Pachylabra 

 carinata). 



