COlfCHIPEKA. 497 



furrowed; umbones anterior; surface granulated; ligament 

 external ; hinge with an obscure tooth or edentulous ; muscular 

 impressions faint ; pallial line deeply sinuated. 



Fossil, 50 species. Lower Silurian — Lower Chalk. United 

 States, Europe, South Africa. 



Suh-genera ? Goniomya, Agassiz. Mya literata, PI. XXII., 

 Fig. 16. (Lysianassa, Miinster, not M. Edwards.) Shell equi- 

 valve, thin, granulated; ligament external, short, prominent. 

 Fossil, 33 species. Upper Lias — Chalk. Europe. 



TelUnomya (nasuta), Hall; Silurian, United States, Europe. 

 Not characterised. 



? Grammysia, Yerneuil. Nucula cingulata, His. Upper 

 Silurian, Europe. Yalves with a strong transverse fold extend- 

 ing from the umbones to the middle of the ventral margin. 



? SedgwicMa (corrugata), M'Coy. = ? Leptodonus (senilis), 

 M'Coy. . Shell thin, ventricose, concentrically ftirrowed in 

 front ; escutcheon long and flat. Silurian — Carb. Europe. 



EiBEiElA, Sharpe, 1853. 



Shell gaping at both ends ; sub -ovate, rounded in front, elon- 

 gated and rather attenuated behind ; punctate-striate ; casts of 

 interior with a large umbonal impression (caused by a cartilage- 

 plate, as in Lyonsia ?) and a notch in front of it. 



Fossil. Lower Silurian. Portugal. 



Ceromya, Agassiz. 



Etymology, Jeeraos, horned, mya, mussel. 



Type, 0. concentrica (Isocardia) Sowerbv, Min. Con. 491, 

 Pig. 1. 



Shell Isocardia-shaped, slightly inequivalve f very thin, 

 granulated, often eccentrically furrowed; ligament external; 

 hinge edentulous ; right valve with an internal lamina behind 

 the umbo ; pallial line scarcely sinuated ? 



Fossil, 14 species. Inferior Oolite—. Greensand ? Europe. 



Sub-genus ? Oresslya (sulcosa) Ag. (Amphidesma and Unio, 

 species, Philippi). Shell oval, rather compressed; umbones 

 anterior, incurved, not prominent ; valves thin, close, smooth 

 or concentrically furrowed; pallial sinus deep. Fossil, 50 

 species. Lias — Portlandian. Europe. The lamina within the 

 posterior hinge-margin of the right valve produces a furrow in 

 the casts, which are more common than specimens retaining th© 

 shell. 



