the economics of Trochus niloticus. 



Fig. 



4- 



Fig. 



5. 



Fig. 



6.- 



Fig. 



7- 



Fig. 



8.- 



Fig. 



9- 



— Young specimen an inch in diameter, showing peripheral tubercles ; enlarged. 



— Type specimen of Astralium pagodus showing an earlier stage in which the tubercles were 



preceded by projecting scales ; magnified. 

 — A shell from which button discs have been cut, drawn after Mr. Seale's photograph ; reduced' 



— Operculum, to show the numerous spirals, the pivot knob on which the whole rotates and the 

 muscle scar of the under side ; reduced. 



— Sector of same, upper side, enlarged. 



— A Papuan bracelet cut from the periphery of Trochus niloticus ; reduced. 



