CHAPTER IX: THE DUCK-BILL SHELLS 

 AND LANTERN SHELLS 



Family Anatinid^^ 



Shells thin, pearly within, granular outside; hinge toothless, 

 pitted; ligament thin, external, with free ossicle; siphons long, 

 united or free; mantle margins united; gills mostly single on each 

 side; foot finger-like; palpi long, narrow. 



A family represented as fossils in all the sedimentary rocks 

 and all over the world, though nowhere very numerous. Tryon 

 lists thirty-six genera. Of these over half are quite extinct, and 

 those with living species form but a scant remnant of the family. 

 Its highest development was reached during the Jurassic Period. 



Genus ANATINA, Lam. 



Shell thin, hyaline, silvery white, smooth, granular toward 

 margins; constriction forms a neck below the posterior, beak- 

 like extension which gapes widely to give exit to the united and 

 sheathed siphon tube; hinge has spoon-like process in each valve; 

 hinge ligament elastic. 



An Oriental genus of thirty species named from a fanciful 

 resemblance of the valve to a duck's bill. 



The Truncated Duck-bill Shell (A. truncata, Lam.), 

 abruptly squared at the posterior end, rounded in front, flat- 

 tened and somewhat incurving on the margin opposite the 

 hinge, is abundant in the Bay of Manila. It is about three 

 inches long. 



There is no American species of this genus. 



THE LANTERN SHELLS 



Genus PERIPLOMA, Schum. 



Shell oval, valves very unequal, left valve deeper, posterior 

 end contracted; lining pearly; hinge with narrow, oblique spoon- 



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