46 



C. HEDLEY. 



held fifty small oysters, was described and figured by 

 Saville Kent from West Australia. 1 



The soft black mud of the mangrove formation is only 

 suited to a small and special fauna. Whole classes are 

 absent, for the mangrove country is shunned by all the 

 Echinodermata, the Actinozoa, and the Sponges. This 

 territory is occupied by a special group of mollusca, mostly 

 air-breathers, usually with solid dull-coloured shells, 

 especially by the family Auriculidae. These range from the 

 fringe of glass wort, locally called " samphire," Salicomia 

 ■australis,* along the high-tide mark downwards as far as 

 the Avicennia grows. Here too, as described previously, 

 sea-snails climb aloft to the greatest height they reach 

 above high water. This Avicennia belt is inhabited by 

 the following molluscan genera: — Onchidium, Salinator, 

 Melaraphe, Zafra, Assemania, Tatea, Potamopyrgus, 

 Plectotrema, Rhodostoma, Leuconopsis, Ophicardelus, 

 Ostrea, Modiolaria^ and Modiola. In the autumn, schools 

 of a marine hemipteron, Halobates whiteleggei, skim over 

 the surface of the mangrove creeks. 3 



Seawards of the tidal forest, there usually occurs an area 

 of soft mud, here is the Holcecius-Pyrazus zone. Holcecius 

 cordiformis (fig. 11) is a small active crab with a purple 

 claw. 



Between the falling and the rising tide, it burrows and 

 builds with such energy that the whole field is covered with 

 little pits and heaps of mud pellets like worm castings on 

 a lawn. The celerity with which the crabs dart to their 

 holes shows a familarity with danger. At low tide they are 



1 Kent, Eep. Austr. Assoc. Adv. Sci., iii, 1891, p. 554. 

 8 An almost pure association of Salicornia, a " Salicornietum," extends 

 for several square miles at the south-east corner of Botany Bay. 

 3 Skuse, Eec. Austr. Mus., i, 1891, p. 174. 



