PYRGOMA 



sliaped testaceous valve, striated or grooved perpendicu- 

 larly in tlie inside ; the operculum biparti^te, each part 

 composed of two valves, which are variable in form, the 

 posterior one being in some species very much elongated. 



There are many recent species of this Genus j those 

 we have represented are the P. crenatum, (Savignum cre- 

 natum, of Leach, in the Brit. Mus.,) and the P. anglicum 

 (Adna anglica, Leach, in 1. c.) the only one that is known 

 upon our coasts, and which is not unfrequently dredged 

 on the coast of Devonshire. 



No fossil species arc known. 



Fig. 1 to 6. Pyrgoma crenatum. 



7. anglicum^ 



