120 ON THE LITTORAL FATJNA OF N. E. AUSTRALIA, 



PeriopMhahnus australis of Castelnau. The mud is literally alive 

 with them when the tide is out. They are about eight or ten 

 inches long with large scales, and fins like seal's flippers, with 

 which they move very rapidly, a kind of leap. They are difficult 

 to catch, but a native boy I had with me was able to knock them 

 over easily with small stones, which he threw with unerring aim. 

 They say that this fish climbs on the roots of the mangrove, but 

 I never saw it do so. It keeps on the wet mud, and is always 

 more or less moistened with the slime. It never comes out on the 

 sand. I think it feeds on the small crustaceans or worms, but I 

 could not ascertain this to my satisfaction. They say that it utters 

 a loud clicking noise, not unlike the crack of a whip. I heard 

 the noise repeatedly, in fact it is quite remarkable and continuous 

 but I could not satisfy myself that it came from the fish. My 

 own opinion was that it was caused by one of the crustaceans. 

 There is however a fish in the Port Douglas Creek, which gives 

 utterance to croaking sounds when captured, of which I was 

 repeatedly a witness. 



On the roots of the mangroves, and sometimes high up on the 

 stems of the trees, four or five species of mollusca are found. Of 

 these two species of Nerita are the most common. Nerita lineata 

 is very abundant, and of large size ; from an inch to an inch and 

 a-half in diameter is the usual size. The natives have used them 

 extensively as an article of food, for large mounds of them are 

 seen in the sandy banks of the creeks near Bowen, with quite a 

 heap of the shelly opercula. They do not climb high up on the 

 trees. This species has a wide range through the Indian Archi- 

 pelago, and in Australia as far south as Moreton Bay. It is 

 surprising that it was not known to Linnaeus : as all the other 

 Indian Neritas seem to have passed through his hands. Side by 

 side with other species, but by no means so common, is the iV. 

 atropurpurea of Eecluz. It is apt to be mistaken for N. lineata, 

 though it is smaller. I was collecting the radulas of the latter 

 and did not observe that I had got N. atropurpurea, until I f oujid 



