COKCnVLlA—DITHYRJ xxxiii. 



33. CrassiKa. 



* maroine interno mteserrimo. 

 witii the inner margin very entire. 



i, subrhoniboidea, aiitice truncata, transversim rugosd. 



truncate at the anterior side, and wrinkled 

 transversely. 



2. Scotica, orbicularis, costis transversis rotundatis. 



orbicular, with rounded transverse ribs. 



** margine interno denticulate. 



with the inner margin toothed. 



3. sulcata, orbiculuris, costis transversis rotundatis. 



orbi< iilar, with rounded transverse ribs. 



C4. Myrtea 

 1. spinifera, Myrtea. 



35. Cyprina. 



1 , Islandica, area ohsoletd, dentibus tribus own laterali remoto. 



the area obscure, with three teeth and a remote 

 lateral one. 



2. (jonipressa, transversim costata, dentibus duobus cum laterali. 



transversely ribbed, Avith two teeth and a lateral 

 one. 



i5. triangularis, Itcvis, valvu altera tridentatu. 



smooth, with three teeth in one valve, 

 * o 



