CONCHOLOGY. 33 



ed ; covered with a dark yellowish epidermis ; inside white ; 

 wrinkled transversely. 



2. Anatina. The Duck's Bill. Ten species. 

 Shell elongated oval, very thin, fragile, semipellucid ; 

 much inflated at one end like a duck's bill, whence it de- 

 rives its common name ; equivalve, very inequilateral ; hinge 

 toothless ; the anterior side rounded and much longer than 

 the posterior ; ligament interior affixed to a bony spoonlike 

 process in each valve, and sustained by a lateral plate run- 

 ning obliquely into the interior of the shell. 



Anatina laterna. Anatina trapezoides. 



A. truncata. A. rugosa, 



A. subrostrata. A. imperfecta. 



A. longirostris. A. myalis. 



A. globulosa. A. rupicola. 



A. subrostrata. The beaklike Anatina. 



Species equivalve and regular. • 



A. myalis. The Mya-like Anatina. 

 Species inequivalve. 



A. trapezoides. The trapezium-shaped Anatina. PI. 

 12, fig. 5. 



Species with a moveable tooth or calcareous piece upon 

 the right valve, lodged in the angle formed by the spoonlike 

 process. 



FAMILY V. 



Mactracea. Seven genera. 



1. Lutraria. Eleven species. 

 This genus was taken from the Mactra, and is perfectly 

 distinct, as it wants the lateral teeth. It is called Lutricola 

 by De Blainville, from its lurking in sand or mud at the 

 mouths of large rivers. 



Shell inequilateral, orbicular, sub-triangular or trans- 

 E 



