454 Journ. of the Asiat. Soc. of Bengal. [Nov. & Dec., 1915, 
the study of the shells of the Lake of Tiberias, which has been 
undertaken by several conchologists and is summarized in Mr. 
vat - 
lake family by family, after making a few general remarks on 
their common peculiarities. 
common in lakes in similar latitudes (e.g. Limnaea, Planor- 
Physa tiberiadensis, which are common enough in the Jordan 
within a few hundred yards of the shores of the lake, find it 
difficult to live in its waters. Mr. Preston regards the thick- 
ness of the shells of the Mollusca that do so as being ‘‘ probably 
due to a surfeit of suspended mineral matter in the water of 
the Lake.’’ I am not quite sure what this means, but it seems 
to me improbable that the thickness of the shells is due to any 
preponderance of calcareous salts. Analyses do not show any 
great amount of free calcium in the water, and if they did it 
would not necessarily be utilized by the molluscs, most of which 
live also in water of more normal composition. There 1s 
no evidence in the case of widely distributed species that the 
shells of individuals from the lake are thicker than those from 
other localities. My own view is that there is something in 
c e 
noteworthy in the case of the Unionidae. Dead shells are 
frequently dredged up that have retained their natural form in 
1 Arch. Mus. @ Hist. nat, Lyon U1 inl 
- nat, »p. 108 (1883). Lortet refers mainly 
to dead shells found at great depth: | but Abas oo same phenomenon 
re wae nis: shallow water. I do not think that depth has anything to 
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