PRESIDENTIAL ADDRESS. 



43 



break into the double, and if still harder pressed the whole 

 troop burrows into the ground, with a spiral motion and 

 vanishes from sight. 1 



Fig. 9. The military crab Mycteris longicarpus, from the estuary mouth. 



Another characteristic form is the subterranean snail 

 Polinices plumbeus (fig. 10). Crooked furrows in the sand, 





', '.•";• 



Fig. 10. Subterranean snail Polinices plumbeus, fully extended. 



sometimes a couple of feet in length, show where the 

 mollusc has burrowed, an inch or so beneath the surface. 



1 Saville Kent, Naturalist in Australia, 1897, p. 242. 



