CO^GEYLIA—DITHYRA. xv. 



39. Pectunculus. — Cardo arcuatus, dentibus numerosis. 



Hinge in a curved line, with numerous teeth. 



*** Cardo dentibus primarus et later alibus. 



Hinge with both primary and lateral teeth. 



16. Amphidesma. — Dentes primaru cochleariformes. 



The primary teeth spoon-shaped. 

 56. Cyclas. — Dentes primaru minuti divergentes, lateralibus valvas 

 alterius didymis. 



The primary teeth minute and divergent, with the 



lateral teeth of one valve double. 

 55. Mysca. — Dentes primaru transversi crenulati, lateralibus valves 

 alterius didymis. 



The primary teeth transverse and notched, with 



the lateral teeth of one valve double. 



34. Myrtea. — Valva altera unidentata cum laterali utrinqu^, altera 



bidentata lateralibus obsoletis. 

 In one valve a single tooth and a lateral one each 

 side, in the other valve two teeth with the lateral 

 ones obscure. 



35. Cyprina; — Dentes primaru duo vel tres, laterali remoto. 



The primary teeth two or three, and a remote 

 lateral one. 

 31, Don AX. — Testa cuneata, ligamento ad latus brevissimurn. 



Shell wedge-shaped, with the ligament at the 

 shortest side. 



