PRESIDENTIAL ADDRESS. 47 



vigorously hunted by such enemies as gulls, herons, bitterns 

 and rats. 



Fig. 11. The mud-flat crab, Holcecius cordiformis. 



Their neighbour the Sydney Whelk, or Hercules Club, 

 Pyrazuslierculeus^ is more lethargic. This brown massive 

 and knobbed shell, three inches long is strewn about in 

 great number (text fig. 12, and Plate VII, fig. 12). Oppo- 

 site the aperture the shell is broadened by a varix which 

 forms a sole to support it from sinking too deeply. Oysters 

 and barnacles sometimes ride on the back of the shell. 



Fig. 12. The Hercules Club shell, Pyrazus herculeus, from 

 the open mud flat. 



1 Hedley, Proc. Linn. Soc. N.S. Wales, xxx, 1906, p. 529. 



