PINNA 



There is a peculiarity observable in many Pinnae, 

 which has undoubtedly given rise to the appellation of suh- 

 quadrivalvis applied to one species by Lamarck, and that of 

 tetragona to another by Brocchi; it consists of a longitudi- 

 nal division of the internal pearly coat, commencing at the 

 anterior point within, and continuing rather more than 

 half way towards the centre of the posterior side : a cor- 

 responding angle is frequently to be seen on the outside ; 

 and it is remarkable that these shells readily break in the 

 direction of this line. 



We have represented at 



Fig. 1. The beautiful Pinna serrata of Solander, from the specimen in the 

 Tankerville Collection. 



2. The inside of a single valve of P. nigrina, to shew the muscular 

 impressions and the ligament. 



