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



and Cassidula anguUfera, are very solid shells ; in fact none of those 

 living on the mangrove are thin except Cerithidea decollata. 



Imbedded in the mud and quite within reach of salt water, but 

 generally not very close to the sea are large numbers of Cyrena 

 Juhesi, Deshayes, (Proc. Zool. Soc. 1854). This is a very solid, 

 large, ovately trigonal shell, irregularly and lightly striate with 

 and when fresh covered with conspicuous, shining, olive periostraca 

 which easily flakes off. Some of the lines of growth are often 

 eroded, and the umbones always are. This erosion it appears to 

 me is the work of some parasite, and not as many think, from the 

 influence of fresh water. The hinge teeth are three in number, 

 with two of them distinctl}^ bifid at the apex. The lateral teeth 

 are distant, one (the anterior) being a blunt tubercle. I enter 

 into this detail because this mollusc is the common form in all 

 the brackish water streams or estuaries, I visited in North-East 

 Australia. I found it in the Endeavoui' Eiver, in the Daintree, 

 the Herbert, Port Douglas Creek, Eoss Creek, the Burdekin, and 

 in the mangroves and swamps around Port Denison. The blacks 

 prize it as an article of food, and large numbers of the shells are 

 always in refuse heaps by the side of the mangroves. 



It will be seen from these facts what a great difference there is 

 between the fauna of the mangroves and that of the rocky coast 

 exposed to the sea. Though only a short distance from one 

 another and the water quite salt, there is not one species of shell 

 fish common to both, and the crustaceans seem all to be different 

 as well. The mud has something to do with it, though other 

 circumstances come into play which are well worth an attentive 

 study. 



If I refer now to the fauna of the coral reefs near Port Douglas 

 it must not be thought that my remarks are anything more than 

 as to what came under my observation during a few brief visits. 

 The subject is too immense to be dealt with in an exhaustive 

 manner except by a voluminous treatise. There are many reefs 



