HYDROBIA. 67 



Var. 1. minor. Shell much smaller : spire shorter. 

 Var. 2. decollata. Shell slightly eroded : spire truncate. 



Var. 3. ovata. Shell having a much shorter spire, consist- 

 ing of only 4 whorls, which are more swollen than usual, and 

 the last considerably exceeds one-half of the shell. 



Var. 4. elongata. Shell having its spire proportionally 

 longer, with sometime^ as many as 8 whorls. 



Var. 5. pellucida. Shell clear white, and nearly transpa- 

 rent. 



HABITAT : Abundantly in many estuaries and in brack- 

 ish water in which the admixture of fresh predominates 

 over salt, throughout England and Wales ; and I have 

 also taken it in Larne Lough, Ireland. It occurs in 

 the upper tertiary bed at Clacton, and elsewhere in the 

 estuary of the Thames. Var. 1. Burry River, South 

 Wales (J. G. J.). Var. 2. Burry River, but not in the 

 same part of the estuary where the first variety is found, 

 and Guernsey (J. G. J.). Var. 3. Oxwich marsh, near 

 Swansea (J. G. J.). Var. 4. Arnold's pond, Guernsey 

 (J.G. J.). Var. 5. Manorbeer, Pembrokeshire (J. G. J.) ; 

 Scarborough (Bean) : very rare. This species inhabits 

 similar situations along the sea-coasts of Sweden, France, 

 and Portugal, as well as of Algeria. 



H. ventrosa is gregarious, and sometimes lives in com- 

 pany with H. ulvce, which however is more of a marine 

 than a freshwater species. The latter is never found 

 out of the reach of the tide, and inhabits the mud flats 

 and ooze ; while the present species usually lives in ponds 

 and ditches into which the sea only flows at high water 

 or in spring tides. The habits of this species are more 

 active than those of H. ulvce; and I have observed that 

 when they are found together the latter may be seen 

 crawling slowly over the mud and Ulva at the bottom of 

 shallow pools, while the other seems to disport itself by 



