ilO MADRAS FISHERIES BULLETIN VOL. XlV, 



only by the sea-spray at high tide. In these the internal surface of 

 the mantle is undergoing modification on the lines seen in the lung 

 chamber of Pachylabra ; another demonstration is afforded us here 

 of how land gastropods have evolved in the past. It is significant 

 also that the operculated land snails and pond snails {Viviparidac) 

 agree with the periwinkle in the arrangement of the teeth on the 

 radula — in each row a broad median tooth flanked by three some- 

 what similar ones on each side. In the periwinkles the radula is 

 peculiarly long, the hinder end being coiled up like a spare rope, 

 in a pocket at one side of the gullet. 



In Europe great quantities are used as food, but in India they 

 are put to no useful purpose. They are common at Cannanore and 

 at Pamban and the neighbourhood. An allied Indian genus 

 Cremnocoiichiis has entirely abandoned life in the sea and has taken 

 permanently to the land. 



The next family, that of the HORN-SHELLS or Cerithiidae, is 

 another with a tendency to migrate from the sea to the land. All 

 have the apex of the shell drawn out into a long spire, simulating 

 the appearance of the true Turret shell, yet to be described, but 

 differing in having the mouth aperture widely channelled and with 

 the lip thickened and everted ; the whorls are usually ornamented 

 with small tubercles or with varicose ridges marking the position 

 of the lip at different dates during growth. 



The marine species are mostly littoral ; Ceritliiiim obeliscns, is one 

 of the biggest of several that are common in sheltered bays and 

 saline backwaters. At Ennur and Tuticorin a small species, 

 Potamides cingulatiis (Fig. 5), is often found in multitudes on mud-flats 

 and at the edge of the tide, playing the part of humble scavengers; 

 lime-kiln women collect them at Tuticorin to be burnt into the best 

 quality of lime for whitewashing, in specially small kilns used for 

 this purpose. Two large species, the HORN-SHELLS proper, be- 

 longing also to the genus Potamides, and undoubtedly derived from 

 the marine Cerithium, are found in abundance crawling in the mud 

 in the mangrove swamps of the Kistna and Godavari deltas, more 

 often out of water than in it. These shells are also used for lime 

 burning. One species, Potamides paliistris, is easily recognized ; it 

 is obviously a gigantic Cerithium ; the other, often called Telesco- 

 pium fusciiHi, has a smooth shell without tubercles or ridges. It 

 may grow to 4 inches in length and village boys in the Godavari 

 hamlets use it as a spinning top, a feat requiring great skill to 



