BY THE REr. J. E. TENISON- WOODS, F.G.S., F.L.S., ETC. 121 



1 had some very distinct opercula amongst those of JV. lineata. 

 That of N. lineata is large and rough, completely covered with 

 granulations of light color. That of N. atropurpurea is smooth, 

 highly polished, and of dark blue-black color. 



Occasionally there is found upon the mangroves, but rather 

 high up on the branches small groups of Cassidula anguUfera, I 

 never noticed any other species though A. auris-judcd, is common 

 on the mangrove further south. 



Cerithium fPyrazusJ sulcatum, Born, is found occasionally. 

 Cerithidea decollata'^ Linn., is very common in places far out of 

 reach of the tide marks and far above high water, I have found 

 the latter on small stems of Melaleuca leucodendron which is rather 

 abundant outside the margin of the mangroves on the flooded 

 flats. Littorina scalra, is also abundant and of large size. The 

 range of this species is very great. It is common on the Avicennia 

 mangrove of Port Jackson, though of small size and variable 

 color, and it extends along all the coast as far as it is known, in 

 N.E., N. and N.W. Australia. But it is unknown off mangrove 

 swamps, in fact it only flourishes upon them. The shell of this 

 species is thin and translucent. I presume that the mollusc is a 

 vegetable feeder and may perhaps live upon land plants as it is 

 always found upon them. It always frequents salt or brackish 

 water, but the latter not commonly, and in water so very nearly 

 like the sea that it can scarcely be called brackish, except for a 

 very short time during each tide. Still there are times when the 

 animal must be exposed to the influence of quite fresh water, 

 perhaps for some days during periods of flood. This would be 

 fatal to many marine mollusca, but is borne evidently without 

 harm by Littorina scalra. Fresh water is instantly fatal to Echini 

 and starfishes. I think I may say that the shell of Littorina scahra 

 is the thinnest of any marine shell known to me, and that in this 

 feature it approaches the fresh water shells. That the habit of 

 living on the roots of trees is not sufficient to account for this, is 

 seen from the fact that Nerita lineata, Cerithium fPyrazus J sulcatum 



