The Cambridge natural history . t a comparatively small proportionare inequivalve. The dorsal margin is adjacent to, the ventral marfjin oppositet(j, the umhones. The anterior ix\\<\. jiostcrior margins are respec-tively the front and hinder edges of the shell. The muscles which serve to close the valves leave im^ircssionson tlie inner surface of each \;d\e. These, when both musclesare present, are known as the anterior and iiostcrlor adductor 2/0 PARTS OF THE SHELL IN BIVALVES imjyressioois. The impression produced by the muscular edge ofthe mantle, which ciu-ves downwards and backwards fr
The Cambridge natural history . t a comparatively small proportionare inequivalve. The dorsal margin is adjacent to, the ventral marfjin oppositet(j, the umhones. The anterior ix\\<\. jiostcrior margins are respec-tively the front and hinder edges of the shell. The muscles which serve to close the valves leave im^ircssionson tlie inner surface of each \;d\e. These, when both musclesare present, are known as the anterior and iiostcrlor adductor 2/0 PARTS OF THE SHELL IN BIVALVES imjyressioois. The impression produced by the muscular edge ofthe mantle, which ciu-ves downwards and backwards from theanterior adductor impression, is known as the imllial line. Inshells with only one muscle it is represented by an irregidar rowof small marks, or disappears altogether {Ostrect). The pfdlialsinus is produced by the muscles which retract the siphons,and is most marked in those genera in which the muscles arepowerful and the siphons large ( Tellina, My a). It is entirelyabsent in genera possessing no retractile Fig. 184—Left valve of Venus gnidia L. :A, anterior, B, i:)Osterior, C, dorsal,D, ventral margin, AB, length, CD,breadth of shell. , anterior ; ^).771., posterior adductormuscle ; 2h pallial line \ , pallial sinus;I, ligament ; hi, lunule ; u, umbo ; c,cardinal teeth ; a. I, anterior lateral tooth ;2^.1; posterior lateral tooth. Fig. —Eight valve of Lucina tigerinaL. : A, anterior, B, posterior, C, dorsal,D, ventral margin; AB, length, CD,breadth of shell. a. m, anterior ; }). in, posterior adductormuscles ; p, pallial line ; /, ligament ; n,umbo ; c, cardinal teeth : , , ante-rior and jiosterior lateral tooth. Right and Left Valve.—The simplest way of distinguishing thevalves as right and left is to hold the shell in such a way thatthe siphons point towards the observer, and the mouth awayfrom him ; in this position the valve to the right is called theright valve, and the valve to the left the left vcdve. If, however,the animal
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
