AND OTHER FAMILIES. 187 



Symphynota discoidea. Plate XI. fig. 33. 



Testd subi-hombed, compressd, transversa, inxquilaterali, valviilis tenuissimis, 

 postice connatis ; natibus paiduni undulatis, compressis ; dentibus in valvulu 

 utrdque lineam simplicem facienlibus ; margaritd alba et iridescente. 



Shell subrhomboidal, compressed, transverse, inequilateral ; valves very thin, con- 

 nate behind ; beaks slightly undulated, compressed ; teeth in both valves forming a 

 simple line ; nacre white and iridescent. 



Hab * G. B. Sowerby. 



My Cabinet. 



Cabinet of Dr Burrough. 



Cabinet of W. Hyde. 



Diam. 1-2, Length 2-4, Breadth 3-9 inches. 



Shell subrhomboidal, compressed, transverse, inequilateral, finely 



wrinkled ; substance of the shell very thin ; posterior slope elevated 



into a moderately high wing, which is connate ; beaks very slightly 



undulated, compressed; ligament linear; epidermis dark brown; teeth 



in both valves forming a simple, continuous, fine curve line ; anterior 



and posterior cicatrices both distinct ; dorsal cicatrices situated in the 



centre of the cavity of the beaks; cavity of the beaks almost none; 



nacre white and iridescent. 



Remarks. — I owe to the kindness of G. B. Sowerby, Esq. the spe- 

 cimen here described. He procured it of " a dealer from Holland," 

 and its habitat is unknown. It has the characters of an eastern shell, 

 and probably came from Java. In the outline of the margin it resem- 

 bles the Symphynota magnifica (described in this memoir), but differs 

 from it in being compressed and in the possession of teeth. In the 

 teeth it has a stronger resemblance to the S. hialata (nobis) than to 

 any other species. It is, however, less defined, and the curve is less 

 regular, the posterior portion being nearly straight. In the elevation 

 of the wing it differs totally. Our present shell forms an interesting 



• Dr Burrough has recently obtained it in the rivers of China, and to him I ovre the fine 

 specimen figured. 



