XTiii. COT^QBYLIA—DITHYRA. 



22. LuTRARiA. — Cardo dente cochleariformi, cum dente trigono 

 adjecto. 

 Hinge with a spoon-shaped tooth, and an addi- 

 tional triangular one. 



20. MoNTACUTA. — Testa (squivalvis, dentibus duobus cum fovea 

 interpositd. 

 Shell equivalve, with two teeth in each valve and 

 a cavity between them. 

 18. Ervilia. — Testa cequivalvis, dente unico inter duos obsoletos 

 penetrante. 

 Shell equivalve, with a single tooth closing between 

 two obscure ones. 



J 2. Pandora. — Valva altera dente longitudinali et foveold, altera 

 foveolis duabus longitud'malibus. 

 In one valve a longitudinal tooth and cavity, in the 

 other two longitudinal cavities. 

 1 1 . CoRBULA. — Valva altera dente conico, altera dente cochle- 

 ariformi. 

 In one valve a conic tooth, and a spoon-shaped 

 tooth in the other. 

 51. Teeebratula. — Valva superior umbone producto apice per- 

 forata. 

 The upper valve with the beak elongated and 

 perforated at the extremity. 



*** Cardo dentibus primariis et lateralibus. 



Hinge with both primary and lateral teeth. 



