LINGUI^A. 



Cwt*/er.— Annales du Mus. v. i. p. 69. 



'tESTA bivalvis, subaequivalvis, ffiquilatera, ovato-^ 

 oblonga, apice trimcata vel subtrimcata, paulunt 

 hiaiis^ hasi siibacata. hnpressiones musculares in 

 uti'aque valva duap. Ligamentu/u nullum. Car do 

 edeiitulus. 



Persuaded as we are that a connect knowledg-e of the 

 nature of slieUs is only to be obtained from the examination 

 and study of the animals which produce them, in a living 

 state, we only yield to the absolute general impossibility of 

 obtaining- the living animals, and the consequent necessity 

 of defining- our Genera in such a manner that they may 

 be recognized without that knowledge ; and therefore in 

 our Generic Character we have avoided taking any no- 

 tice of those accessary circumstances in this Genus, which 

 at once render it so interesting and apparently so anoma- 

 lous. 



The general form of this shell, when the tzoo valves are 

 closed, is an oblong oval, compressed, and much resembling 

 a duck's-bill, they are attached to each other ])y the inter- 

 nal muscles, being suspended to a cylindrical, fleshy, tendi- 

 nous peduncle. Tlie two valves are equilateral, ovately 

 oblong, truncate or subtruncate, and slightly gaping at 

 their apices and poiiited at tlieir base, but somewhat 

 different in their interior construction, one of them having 

 a projection between the two muscuhir isnpressions elon- 

 gated in the same direction as the shell, of which the other 

 valve is destitute, as well as of shelly mattf^r at the point of 

 the base. The muscular impressions are oblong, placed 

 near to each other and to the centre of the shells. A shin- 

 ing, homy epidermis coats both valves. There are no 



