CONCHIFERA. 497 
furrowed; umbones anterior; surface granulated; lgament 
external; hinge with an obscure tooth or edentulous; muscular 
impressions faint; pallial line deeply sinuated. 
Fossil, 50 species. Lower Silurian—Lower Chalk. United 
States, Hurope, South Africa. 
Sub-genera ? Goniomya, Agassiz. Mya literata, Pl. XXII., 
Fic. 16. (Lysianassa, Minster, not M. Edwards.) Shell equi~ 
valve, thin, granulated; ligament external, short, prominent. 
Fossil, 33 species. Upper Lias— Chalk. Europe. 
Tellinomya (nasuta), Hall; Silurian, United States, Hurope. 
Not. characterised. 
P Grammysia, Verneuil. Nucula cingulata, His. Upper 
Silurian, Europe. Valves with a strong transverse fold extend~ 
ing from the umbones to the middle of the ventral margin. 
? Sedgwickia (corrugata), M‘Coy. = ? Leptodonus (senilis), 
M‘Ooy. Shell thin, ventricose, concentrically furrowed in 
front ; escutcheon long and flat. Silurian—Carb. Jurope. 
RIBEIRIA, Sharpe, 1853. 
Sheli 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. 
_ Hiymology, keraos, horned, mya, mussel. 
Type, ©. concentrica (Isocardia) Sowerby, Min. Con. 491, 
Hic: 1. 
Shell Isocardia-shaped, slightly inequivalve? 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 ? Gresslya(sulcosa) Ag. (Amphidesma and Unio, 
species, Philippi). Shell oval, rather compressed; umbones 
anterior, incurved, not prominent; yalyes thin, close, smooth 
or concentrically furrowed; pallial sinus deep. Jossil, 50 
species. Lias—Portlandian. Hurope. The lamina within the 
posterior hinge-margin of the right valve produces a furrow in 
the casts, which are more common than specimens retaining the 
shell, 
