I06 MADRAS FISHERIES BULLETIN VOL. XIV, 



Usually about a quarter of an inch across, its low depressed spiral 

 shell is stippled and marbled in dozens of variations and in a range 

 of colour from pink to brown. Some are nearly white, so few and 

 pale are the markings, while others are deep chestnut, so closely set 

 are the spots. Millions must be exported to Europe, for this shell 

 rs one of the chief of those used in the ornamentation of shell-boxes 

 sold at every watering place in England. 



Grouped with the Turbos are the PHEASANT SHELLS [Phasienella 

 spp.), prettily patterned tiny shells that occupy to the Turbos much 

 the same relation as the handsome Umbonium does to the true 

 Top-shells. Their little polished shells are to be found on rocky 

 shores at the edge of pools and in sheltered crevices. They are 

 gregarious and like Umbonium, the patterns of their colouring vary 

 enormously. 



The NERITES show unusual adaptability to varying conditions. 

 Nerita lives in the sea ; one picks it up just below high water mark 

 at Pamban and the Ramnad reefs; the closely allied Neritina \s 

 the fresh-water form, though it may also be found in brackish 

 water. A third genus, Septaria { — Navicella) is still further removed 

 from the ancestral marine form, for it has actually acquired the 

 habit of living in places on the banks of streams where it is only 

 kept damp by spray or the lapping of the water on the rock or tree 

 root or stem to which it adheres. The series of transition forms 

 seen here is an excellent illustration of how fresh-water faunas 

 have arisen and how from these land molluscs may in turn be 

 evolved. 



Considering their size — barely three-quarters of an inch in 

 length — the shells of the Neritas are extremely massive. They live 

 at the edge of the sea and are often tumbled off their lodgment on 

 the rocks by the waves ; were they less strongly built their shells 

 would be broken and destroyed. 



The shell externally shows distinct spiral markings at one side — 

 the apex ; internally in adults the whole cavity is simple and 

 rounded. Study of the life history of Nerita from the very young 

 stages, shows that it begins life with a well-marked spire wound 

 round a central column, the columella. As it grows the columella 

 and whorl partitions are gradually absorbed. It would seem that 

 the animal has to be so busy in strengthening the external wall of 

 its house, that it can spare no limy material for interior decoration. 



