atlgiilar disk of the liiiige of the lower valve, and to the 

 opposite cicatrice in the upper valve, but the ligament is 

 expanded on both sides, so as nearly to cover the triangular 

 disk in both valves. There is a single, large, suborbicular 

 muscular hnpression in each valve. 



The only species of this Genus at present known is the 

 Pedum spmiclf/loideum of Lam. Ostrea spondj/loidea of 

 Gmel. probably so named on account of the near resem- 

 blance of its hinge to that of Spondylus^ from which how- 

 ever it is sufficiently distinct. It approaches nearer io 

 Lamarck^ s Malleus^ particularly in its manner of attach- 

 ment, but the shell is destitute of the foliated substance 

 consisting of fine perpendicular fibres so characteristic of 

 that Genus as well as of Ostrea. It cannot be confounded 

 with any other Genus. 



From the Indian Ocean. No fossil species has yet been 

 discovered. 



