ALBIAtt FOSSILS DISCOVERED AT OKEFORD FlTZPAINE. 7 3 



OSTREA LEYMERIEI (Deshayes MS.) Leymerie. 

 PI. i, fig. 3. 



Ostrea Leymeriei, Leymerie : Mem. Soc. Ge*ol. France, 1842, 

 Vol. 5, part 1, PI. 13, fig. 4. p. 11. Forbes : Quart. Journ. Geol. 

 Soc., 1845, Vol. 1, p. 250. Orbigny : Paleontologie Franchise, 

 Terrains Cretaces, Lamellibranchia, 1846, PL 469, p. 704. Coquand : 

 Monographic Ostrea, Terrain Cretace, 1869, PI. 70, fig. 14-17 ; 

 PI. 71, figs. 6-7, p. 179. 



This is an oyster of variable shape, as it may be oval, oblong, or 

 subtrigonal ; the two latter varieties having been obtained at 

 Okeford Fitzpaine. The largest specimen, selected for figuring and 

 description, has both the valves in contact, though some of the 

 shell has been removed from the right or upper valve to show the 

 extent of the ligamental area. It is oblong and depressed ; 

 right valve smooth and bearing concentric lamellae of growth ; 

 left valve is thicker, more lamellose and irregular than the 

 other, besides bearing the fluted costse ; ligamental region 

 very wide, with a more excavated central depression in the lower 

 valve, and having a pointed dorsal termination which curves 

 anteriorly ; muscular impression (not seen in specimen under 

 description, but well marked in others from the same locality) 

 of large size, squarish outline, deeply cut, and near to posterior 

 side. 



This specimen is of great size, measuring 221 '5 by 180 

 millimetres. 



The species is characteristic of the " Argiles Ostreenes," a 

 deposit forming the base of the Barremian system of France, and 

 so named by Cornuel * in 1840 because of the profusion of this 

 oyster. 



KANGE OF SPECIES. Barremian to Albian. 



LOCALITIES. Atherfield, Sandgate, and in the Haute-Marne and 

 Aube districts of France. 



* Bull. Soc. Geol. France, 1840, Vol. 11, p. 126. Mem. Soc. Gcol, 

 France, 1840, Vol. 4, p. 335 (footnote). 



