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 carti- 

 lage 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 re- 

 curved teeth in each valve, and an 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. ARC A. Plate 9. 

 Animal, a Tethys. 



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

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

 terstices of the opposite valve. Muscular impressions two in each 

 valve. 



