A. lens. 



FAMILY XX. 



BnACHiopoQA. Three genera. 



1. Genus Orbicida. 



Aiiimal. Body much compressed and rounded ; mantle open 

 throughout its whole circumference ; two ciliated tentacular appen- 

 dages. 



Shell. Orbicular, much compressed, inequilateral, very inequi- 

 valve ; inferior valve very thin, adhering, imperforated, the superior 

 patelloid, with the summit more or less inclined towards the 

 posterior side. Inhabits the Norwegian seas. One living species. 

 Two fossil. 



Orbicula Norwegica. 



2. Genus Terebrattda. 

 Ardmal. Depressed, circular or oval, more or less elongated, 

 with two long pectinated labial tentacula. 



Shell. Thin, inequivalve, regular, subtrigonal ; one of the 

 valves larger and more dilated than the other, which is sometimes 

 operculiform ; hinge condyloid, in a straight line and formed by 

 two oblique articular surfaces in one valve placed between corres- 

 ponding projections in the other. Inhabits the sea at the Zetland 

 Islands. Twelve living species. Thirty-seven fossil. 



Terebratula dilatata. 



T. flavescens. 



T. dorsata. 



T. Vitrea. 



T. dentata. 



T. sanguinea. 



Terabratula globosa, 



T. caput-sorpentis. 



T. psittacea. 



T. rotunda. 



T. pisa. 



T. truncata.* 



