No. 6 (1921) COMMON MOLLUSCS OF SOUTH INDIA 



125 



they are exposed to the influence of strong currents during the 

 monsoon, have these ridges particularly strong and prominent 

 giving increased purchase to the muscles connecting the foot with 



the shell. The exterior 

 is covered with a thick 

 velvety coating of 

 golden brown perio- 

 stracum, completely 

 hiding the snowy 

 white porcellanous 



shell beneath. 



The chank is grega- 

 rious and its haunts 

 form distinct "beds." 

 It prefers a sandy 

 bottom where tube 

 worms abound ; these 

 constitute its chief 

 food. These sandy 

 beds are most prolific 

 in depths from 8 to 10^2 

 fathoms off the Tinne- 

 velly coast; in Palk 

 Bay the beds are at a 

 lesser depth and where 

 there is much mud 

 mixed with the sand, 

 this appears to affect 

 the growth of the 

 chanks adversely. 



Other beds occur along the Tanjore and South Arcot coast and 

 extend to some distance north of Pulicat lake. Chanks are found 

 also off South Travancore and in Okhamandal in Kathiawar. In 

 the Andamans a distinct variety (.'' species) occurs with elongated 

 mouth and distinct remains of knobs along the shoulder of the 

 whorls, a type more akin to the ancestral form than the smooth- 

 surfaced shells from the east coast of India, 



The larval development of the chank is typical of that of many 

 of the larger Gastropods and is almost identical with that of the 



Fig. 15, The Sacred Chank [Tnrbinella firti/ji, L.), 



X h 



