PINNA, Auctorum. 



TESTA aequivalvis, obliqua, longitudinals, cu- 

 neiformis, umbonibus anticfe terminalibus, acu- 

 tis, latere postieo plerumque truneato, hiante; 

 basi, margineque antieo (hiantulo) lineam con- 

 tinuam, reetam, obliquam formantibus; liga- 

 mento elongato, per totam dorsi longitudinem 

 continue. Impressiones musculares duae, pos- 

 tica maxima, subcentralis, antica tewninalis, 

 nonnunquam duplieata; impressio nxuscularis 

 pallii irregularis, sinu nuUo, 



Shell equivalve, longitudinal, oblique, wedgesliaped, 

 with the umhones forming a point anteriorly ^ posterior 

 side generally truncated, always gaping; the base and 

 anterior margin, which latter is also somewhat gaping for 

 the passage of the byssus, forming together a straight 

 continuous line : ligament very much lengthened, partly 

 internal, continuing along the whole dorsal margin. 

 Muscular impressions two, the posterior very large, nearly 

 central; the anterior terminal, sometimes double: mus- 

 cular impression of the mantle irregular, without any 

 sinus. 



The Genus Pinna appears to us to be one of the most 

 easily distinguished, indeed we do not know of any Genus 

 with which it can be confounded, except perhaps the La- 

 marckian Mytilus, which alone has the acute terminal 

 umhones so characteristic of Pinna. Mytilus may, hoV- 

 ever, be known by its closed posterior extremity and hy 

 the greater depth of its valves. The Pinned are rather 



