COT^CUYLIA—DJTHYRJ. » 



Character genericus essentialis. 

 Essential generic character. 



A. 



Ligamentum nullum. 

 Ligament none. 



1. Pholas. — Testa transversa^ ovata. 



Shell transverse, oval. 



2. Teredo. — Testa orhictdai'is, hemis'pheerica. 



Shell orbicular, hemispherical. 



B. 



Ligamentum externum. 

 Liii'ament external. 



* Cardo edentulus. 

 Hinge without teeth. 



4. Saxicava. — Testa transversa, latere anfico huutle. 



Shell transverse, open at the anterior end. 

 33. Anodon. — -Testa transversa, sinu marginali antico. 



Shell transverse, with a marginal depression, 

 on the anterior side. 



• 2 A. 



