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XIII. Description of Seven new Species of Testacea. By William 

 George Maton, M.D. F.R.S. cj- A.S. and V.P.L.S. 



Read Nov. 7, I8O9. 



The 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 aestuary of the Rio de la Plata, and who, witli his usual 

 liberality, obligingly presented me Avith specimens, and permitted 

 me to lay a description and figures of tliem 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 matrix, in its dry state, forms a tough, but 



VOL. X. 2v thin, 



