CONCIIIFEP.A. 323 



Shell thin, ventricose, concentrically furrowed in front ; escutcheon long and 

 flat. Silurian — Carb. Europe. 



Ceromya, Agassiz. 



Etym. Keraos horned, mya, mussel. 



Tijpe, C. concentrica (Isocardia) Sowerby, Min. Con. 491, fig. 1. 



Shell Isocardia-shaped, slightly inequivalve ? very thin, granulated, often 

 eccentrically fui-rowed; ligament external; hinge edentulous; right valve 

 with an internal lamina behind the umbo; pallial line scarcely sinuated? 



lossil, 14 sp. Inf. Oolite — . Green-sand ? Europe. 



Sub-genus ? Gresslya (sulcosa) Ag. (Amphidesma and Unio. sp. Phil.) 

 Shell oval, rather compressed ; umbones anterior, incurved, not prominent ; 

 valves thin, close, smooth or concentrically furrowed; pallial sinus deep. 

 Fossil, 17 sp. Lias — Portlandian. Europe. The lamina within the pos- 

 tei'ior hinge -margin o the right valve produces a furrow in the casts, which 

 are more common than specimens retaining the shell. 



? Cardiomorpha, Koninck. ^ 

 Tijpe, C. oblonga (Isocardia) Sby. (not Kon.) Carb. lime. 

 Shell Isocardia-shaped, smooth or concentrically furrowed, umbones pro- 

 minent, hinge edentulous ; hinge-margin with a narrow ligamental furrow, 

 and an obscm-e internal cartilage-groove. 



Fossil, 38 sp. L. Silurian — Carb. N. America, Europe. 



Edmondia, Koninck. 



Ex. E. sulcata. Ph. (T. Pal. Soc. 1850, PI. XX. fig. 5.) Carb. Brit. 



Syn. Allorisma, King (part). Sanguinolites, M'Coy (part). 



Shell oblong, equivalve, thin, concentrically striated, close ; umbones an- 

 terior; ligamental grooves narrow, external; hinge-line thin, edentulous, 

 furnished with large oblique cartilage-plates, placed beneath the umbones, 

 and leaving space for an ossicle ? pallial line simple ? 



Fossil, 4 sp. Carb. — Permian. Europe. 



Lyonsia, Turton, 1822 (not R. Brown). 



Syn. Magdala, Leach, 1827. Myatella, Brown. Pandorina, Scacchi. 



Type, L. Norvegica, PI. XXIII. fig. 10. 



Shell nearly equivalve, left valve largest, thin, sub-nacreous, close, trun- 

 cated posteriorly; cartilage plates oblique, covered by an oblong ossicle; 

 pallial sinus obscure, angular. Structure intermediate between Pandora and 

 Anatina ; outer layer composed of definite polygonal cells. 



Animal with the mantle closed ; foot tongue-shaped, grooved, byssiferous ; 

 siphons very short, united nearly throughout, fringed; lips large, palpi 

 narrow, triangular. 



Distr. 9 sp. Greenland, N. Sea, Norway, W. Indies, Madeira, India, 

 Borneo, Philippines, Peru. 



