42 C. HEDLEY. 



and long slender limbs. 1 Across the beach the swift sand- 

 crab races like foam blown before the gale. And when it 

 stops, so closely does its colour match that of the sand 

 that it can scarcely be detected. This crab breathes 

 through a special pore between the third and fourth pair 

 of legs, and has become so dependent on the air, that it 

 would drown if kept long under water. It digs a deep 

 spiral burrow in the dry sand above the wash of the tide, 

 and feeds on the carcases which the sea throws up and the 

 flies attracted thereto. 



Under masses of decaying sea-weed at the storm drift- 

 line swarm the amphipods Talorchestia qaadrimana and 

 Ochestia macleayana. 2 



THE MUDDY ESTUARY. 



Between the ocean beach and the flats grassed by 

 zostera there is a transition region, passing gradually from 

 rough to calm and from sand to mud. As more shelter is 

 secured the conditions of life become easier, more stability 

 is gained, vegetation appears and the consequent food and 

 safety induce an increase in the fauna. Intermediate sand 

 flats are apt to be arranged in low bars and shallow pools. 

 Here is the Mycteris-Polinices zone. The sand is here a 

 little muddy, more loosely packed than on the open beach, 

 and is usually ribbed by the retreating tide. 3 Such sand 

 ripples are seen through the water in the lower left corner 

 of Plate VI. 



These flats are the parade grounds of a small blue crab 

 Mycteris longicarpus (fig. 9) which marches in squadrons. 

 Their ordinary progress is deliberate, but if pursued they 



1 For this, and the other drawings of crabs, I am indebted to my 

 friend Mr. B. Kinghorn. 



2 Haswell, Proc. Linn. Soc. N.S. Wales, iv, 1880, p. 248. 



3 The formation of ripples on a sandy shore has been discussed by Dr. 

 A. P. Brown, Proc. Acad. Nat. Sci. Phil, lxii, 1912, p. 536. 



