CONCHYLIX—DITHYRA. 33. 129 



the longer side ; inside cliesnut, with the margin plain : 

 hinge with two teeth in each valve, one of them large and 

 the other small. 



33. CRASSINA— Z.^M.4/2CK. 



Testa suborbicularis, €squivalvts, subcequilateralis, clausa 

 Cardo dentibns dnobus in utrdque valvd : lateralibus nullis. 

 Ligamentum externum, ad lahts longius. 



Shell somewhat orbicular, equivalve, nearly equilateral, closed. 

 Hinge with two teeth in each valve : lateral teeth none. Liga- 

 ment external, at the longer side. 



The general outline of this genus, more especially the position 

 of the ligament, will sufficiently distinguish it from the Capsa and 

 the Psammobia. 



=X< 31argine interno integerrimo. 1-2. 

 With the inner margin very entire. 



Crassina testd orbiculo-rhombed, antice truncatd, strus trans- subrhomboi- 

 versis rugosis longitudinalibusqne confertis. **" ' 



Shell orbicular-rhombic, truncate at the anterior side, with rough 

 transverse striae and close lon";itudinal ones. 



