CORBULA. 



formation in the Isle of Wight, agree with the recent 

 shell from the Rio de ]a Plata. 



The Corbulse may properly he described as inequi- 

 valve, (although one species is known whose valves are 

 very nearly alike,) nearly equilateral, transverse, gene- 

 rally gibbose, not gaping bivalves; but the Myae are 

 rather irregular though equivalve shells. A single, gene- 

 rally conical, pointed, recurved, (ascending) tooth in each 

 valve, with a small, sometimes very deep hollow by the 

 side of it for the reception of the ligament, or the tooth 

 of the opposite valve. Ligament internal, fixed to the 

 tooth of the smaller valve, and inserted in the hollow by 

 the side of the tooth in the larger. Muscular impressions 

 two, distant, lateral, rather irregular. Muscular impres- 

 sion of the mantle with a very small sinus ; and in this 

 respect it dilfers from Mya, in which Genus the sinus is 

 very large. 



The Corbulee are marine; the number of recent spe- 

 cies is rather considerable, but they are rare, except the 

 Corb. Nucleus, of Lam.; Mya inequivalvis of English 

 authors, which is frequent on many parts of our coasts : 

 one or two others are also inhabitants of the British Isles. 

 Fossil species are also rather numerous ; they occur in the 

 Green Sand, London Clay, and Crag, in England^^and iu 

 the corresponding formations in other countries. 



1 & 2. Corbula gallica. 'Sf^OT 



3, — Nucleus, : dni 



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