THE LINNEAN GENERA. IX 



9. DONAX.— Plate 6. 

 Animal, a Tethys. 



Shell, bivalve, equivalve, of unequal sides, the anterior side very 

 short and very obtuse ; generally crenulated on the margin. 

 Hinge with two cardinal teeth, either on each valve, or on one 

 only : a single remote lateral tooth in the posterior side. 



10. VENUS.— Plate 7. 

 Animal, a Tethys. 



Shell, bivalve, equivalve, with a heart-shaped depression on the car- 

 tilage slope. Hinge with three approximate teeth in each valve, 

 the lateral ones inclining a little outwards. 



11. SPONDYLUS.— Plate 9. 

 Animal, a Tethys. 



Shell, bivalve; valves unequal, eared, spiny or rugged ; one convex, 

 the other rather flat and adherent. Hinge with two strong 

 recurved teeth in each valve, and au intermediate hollow for 

 the ligament. 



12. CHAMA.—Plate 9. 



Animal, a Tethys. 



Shell, bivalve, irregular; beaks recurved, unequal. Hinge with a 

 single oblique tooth, thick and coarse ; articulated into a cavity 

 in the opposite valve. Two muscular impressions in each valve. 



13. ARCA.— Plate 9. 

 Animal, a Tethys. 



Shell, bivalve, equivalve; beaks prominent, and separated by a chan- 

 nel. Hinge, composed of numerous teeth, inserted into the 

 interstices of the opposite valve. Muscular impressions two in 

 each valve. 



