MALACOZOA. TKOPIOPODA. LAMKLLIUHANC'HIATA. 219 



GENUS 5. ANATIXA. Shell oval, inequivalve, inequi- 

 lateral, very thin, brittle, gaping and more or less trun- 

 cate behind ; umbones small ; hinge with an abrupt sinus 

 and a projecting spoon-shaped lamina. Anas, a duck ; 

 eaten by sea-ducks. Lamarck. 



1 . Anatina prcetenuis. Shell ovate, rather compressed, 

 the anterior end rounded, the posterior subtruncato- 

 rotundate and roughish with minute prominences. 

 Prcetenuis, very thin. 



2. Anatina truncdta. Shell subovate, rather com- 

 pressed, the anterior end rounded, the posterior narrowed, 

 subtruncate, and roughish with minute prominences. 

 Truncatus, cut short. 



GENUS 6. THRACIA. Shell ovato-oblong, inequivalve, 

 inequilateral, very thin, brittle, gaping and more or less 

 truncate behind; umbones rather prominent ; hinge with 

 a horizontal, oblique, concave tooth. Deshayes. 



1. Thrdcia dedivis. Shell oval, convex, very thin, 

 with the posterior end narrowed, compressed, roundly 

 truncate. Declivis, sloping. 



2. Thrdcia pub escens. Shell ovato-oblong, somewhat 

 compressed, very thin, with the posterior end truncate, 

 the surface very minutely punctulate, roughish behind. 

 Pubescens, downy. 



FAMILY II. MYINA. 



Animal elliptical, ovate or oblong, compressed, with 

 the mantle closed beneath, open in front for the foot, 

 and forming behind two long united or separated tubes ; 

 foot small, compressed, tapering ; shell elliptical, oval, 

 or oblong, generally inequivalve, gaping at both ends ; 

 the hinge with a concave tooth in one valve, and a cor- 

 responding depression in the other for the ligament. 



GENUS 1. MYA. Shell ovate or oblong, inequivalve, 

 inequilateral, convex, gaping at both ends ; umbones 

 small ; hinge strong, with a horizontal spoon-shaped 

 process ; ligament internal. Mva, a kind of shell-fish. 

 Linnaeus. 



