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The most remarkable species of the fresh-water shells 
is one recently discovered by Mr. Petterd, and belonging 
to the rare genns Gundlachia. It has been named Gund- 
lachia Petterdi. It is a very small species, not much unlike 
a small specimen of Ancylus lacustris with a portion of the 
mouth of the shell dilated widely like Ancylus fluviatilis. 
The texture of the shells is very similar to Ancylus lacus- 
tris, and it is found in similar habitats. 
Mr. P. exhibited specimens of the Tasmanian shells, and 
also spoke of several introduced European species which 
have become, or are becoming, naturalised in that country. 
Mr. Edwaed Collier, who was present as a visitor, men- 
tioned that the fresh-water species of shells of Tasmania 
were, with two exceptions, entirely different from those of 
Australia, which suggests that the separation of the two 
islands must have been remote. 
Mr. Plant, F.G.S., exhibited a slab of flexible sandstone 
12 inches long by wide and f thick. When supported 
at each extremity the deflection in the centre amounted to 
on one side, and when turned over to of an inch. It 
also had a sensible deflection when tested edgeways. 
Sandstones having this flexibility are obtained from 
Georgia, South Carolina, the gold and diamond districts in 
Brazil, and in the vicinity of Delhi, India. In Capt. 
Burton’s “ Highlands of Brazil,” vol. 1, p. 878, he thus 
states what he observed on the spot about the Brazilian 
variety of this stone. 
“The older writers apply the term ' Itacolumite ’ to a 
white or yellow sandstone, flexible like a plate of gutta- 
percha.” It greatly resembles that of the Lower Himalaya, 
in which thin layers of the silicious granular matter are 
associated with small plates of talc. The ‘Pedra Elastica’ was 
described two and a half centuries ago by Padre Anchieta. 
Dr. C. Wetherill (American Jour. Sci. Art.) declares that the 
