COl^CHYUA—DITHYRA. xxxvii. 



3. exoleta, orhiculo-cordata depressa, striistransversis capillaceis. 

 orbicular heart-shaped and flattish, with trans- 

 verse capillary striae. 



1. sinuata, ohovato-cordata tumida, striis transversis capillaceis. 

 ohoval heart-shaped tumid, with transverse 

 capillar J' striae. 



5. Tigerina, orhiculo-cordata, striis decussatis. 



orbicular heart-shaped, with decussate striae, 



38. Arca. 



* 7nargine interno crenulato. 

 with the inner margin toothed. 



1. Noae, atignlo inarginis superi prodactiori. 



with the angle of the upper margin longer. 



2. fusca, augulo margitiis superi breviori. 



with the angle of the upper margin shorter. 



3. tetragona, suhtetragona, casta loiigitudinali. 



ticarly square, with a longitudinal rib. 



4. reticulata, costis longitndinalibus barbatis decussatis. 



with bearded decussate longitudinal ribs. 



** maroine interno inteoerrimo. 

 the inner margin very entire 



/). ])erforans, latere antico angvluto. 



angular at the anterior side. 



39. Pf.ctunculus. 



