ORBICtJLA. 



Orbicula et Discina. 

 Lam. Hist. Nat. des Anim. sans vert. 



TESTA insequivalvisj subirregularis, suborbicu- 

 laris, compressa, valvuld superiore pateiliformi ; 

 infer lore affixdy planulaid: impressioncs muscula" 

 res, in utraque valvula, quatuor, duce majus- 

 cul8e, approximatse, subcentrales, 6^?;^^^ minores, 

 posticae, siibmarginales, distantes. F is stir a 

 ligameiiti adha^sionis, in valvula inferiore, 

 subcentralis, processii obtiisiusciilo intus ter- 

 minata. Cardo edentuliis, Ligamentum carditis 

 nullum. 



The Genus Orbicula was established by Lamarck in 1801, 

 but as his character of it was taken entirely from Miiller's 

 plate of Patella Anomala in " Zoologia Danica^'^ and not 

 from the shell itself, it was necessarily very incomplete, 

 and Lamarck was himself almost unacquainted with his 

 own Genus. Subsequently we have had an opportunity of 

 examining many perfect specimens, which have enabled 

 lis to give an amended generic character and several 

 observations, which are published in the 13th vol. of the 

 Transactions of the Linnean Society/' where we have 

 also endeavoured to clear up some confusion which has 

 been created by the mistakes of several authors, and 

 where we have shown that Lamarck's new Genus Discina 

 ought to be entirely expunged, as being actually formed 

 from some specimens of OrUcula Norvegka vrhich we sent 

 to him. 



