128 MADRAS FISHERIES BULLETIN VOL. XIV, 



The breeding season, when the capsules are fashioned and 

 rooted in the sand, extends throughout January, February, and the 

 first half of March. Some divers assert that new capsules are also 

 to be found in June and July, but I have had no opportunity to test 

 this statement. The sexes being separate the divers have several 

 stories to tell anent the breeding habits. Among others they 

 assert that the females are the larger and are attended each by a 

 number of smaller males, who assist in the making of the capsules ! 



The chank is an excellent instance of the acquisition by an 

 animal of characters which appear, for all practical purposes, 

 absolutely perfect to enable it to hold its own with ease in its 

 struggle for existence. Against every one of its known enemies it 

 has evolved suitable means of defence. The massive strength of 

 its shell protects it from the attacks of all ordinary fishes ; the 

 density and thickness of its periostracum give during youth and 

 maturity adequate protection against the insidious attacks of the 

 boring sponge Cliona and its shell-burrowing congeners; the strong 

 capsule it constructs for its young gives them protection till they 

 reach a self-supporting stage endowed even at this early period 

 with a fairly strong and resistent shell— one cannot crack it between 

 one's finger and thumb. Its semi-burrowing habits give it defence 

 against those fishes which have the habit of snapping off the 

 protruded feet of gastropods. Finally the pale yellowish-brown 

 periostracum assimilates closely in colouring to the sand and 

 should be a further protection against its discovery by enemies ; 

 to this form of protection I am, however, not inclined to assign 

 great value, for chank divers can distinguish the presence of a 

 chank even when half buried in the sand, and if they can, I feel 

 assured that predatory fish are equally clever. 



As chanks grow old, their resisting powers diminish, the 

 protecting periostracum receives damage and the burrowing 

 sponge Cliona, obtains a lodgment in the shell. Once there it 

 runs its branching tunnels everywhere in the substance of the 

 shell, converting it into a honeycombed mass. I greatly doubt if 

 this contributes except indirectly to the death of the chank. This 

 probably occurs usually from senile decay on beds that are not 

 fished commercially. It is noteworthy that beds which have not 

 been fished for some years, contain great numbers of Cliona- 

 burrowed shells, whereas on beds that are fished regularly, the 



