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XIII. Description of Seven new Species of Testacea. By William 
George Maton, M.D. F.R.S. & A.S. and V.P.L.S. 
Read Nov. 7, 1809. 
Tus shells which I am about to describe were referred to me by 
the Right Hon. Sir Joseph Banks, Bart., K.B., who received them 
from the estuary of the Rio de la Plata, and who, with his usual 
liberality, obligingly presented me with specimens, and permitted 
me to lay a description and figures of them before the Linnean 
Society. 
It is singular that so many new species should have been 
found collected together in one spot, and still more so, that no 
one species before described should have formed part of the as- 
semblage. I am induced to think that they were brought down 
together by some of the tributary streams of the Rio de la Plata, 
from interior parts of the South American continent not hitherto 
explored by conchologists; the name of one of these streams 
proves that it abounds with natural productions of this tribe, for 
it is called Rio di Conchas. Many of the bivalves were found 
enveloped in the gelatinous matrix (if it may be so denominated) 
in which they were first deposited, and to which probably all testa- 
ceous creatures remain attached (unless removed by mechanical 
violence) until the calcareous covering which is to form their pro- 
tection has acquired the requisite degree of firmness. In the 
present instance, this matriz, in its dry state, forms a tough, but 
VOL. X, 2U thin, 
