?4 ALBIAtf FOSSILS DISCOVERED Al OKfiFORD FlfZPAINfi. 



EXOGYRA SINUATA, J. Sowerby. 

 PI. ii., figs. 2-3. 



Gryplicea sinuata, J. Sowerby : Mineral Conchology, 1822, 

 Vol. 4, PI. 336, p. 43. 



Exogyra aquila, Goldfuss : Petrefacta Germanise, 1833, Vol. 2, 

 PI. 87, fig. 3, p. 36. 



Exogyra sinuata, Leymerie : Bull. Soc. Geol. France, 1840, 

 Vol. 11, p. 124. 



Ostrea aquila, Orbigny : Paleontologie Francaise, Terrains 

 Cretaces, Laraellibranchia, 1846, PL 470. p. 706. Coquand : 

 Monographic Ostrea, Terrain Cretace, 1869, PI. 61, figs. 4-9, 

 p. 158. 



A well-known shell belonging to one of the most ponderous 

 forms of the Ostreidse, It possesses a very convex lower valve, 

 which is subcarinated in young specimens but rounder and more 

 massive in the adult stage, and bearing external sculpturing of 

 coarse lamellose lines of growth ; the right or upper valve is 

 depressed, operculiform, and much smoother than the other ; the 

 beaks of both valves are postero-laterally incurved and more or 

 less spiral, this latter feature being characteristic of Say's genus 

 Exogyra. 



E. Couloni, a closely related species, differs from E. sinuata in 

 possessing a lateral expansion when young, which, at a later stage, 

 disappears, the shell then becoming singularly narrow in the adult 

 stage ; the lower valve is more strongly carinated and sometimes 

 plicate ; it also characterizes a lower horizon, viz., the Hauterivian 

 division of the Neocomian system. 



Continental authors have endeavoured to suppress the familiar 

 specific name attached to this shell on account of Lamarck's usage 

 of Ostrea sinuata for a recent specimen in 1819, but as Sowerby 

 applied the generic title of Gryphcea, and not Ostrea, to his shell 

 it is obvious that no change in specific nomenclature is needed. 

 Dimensions. 120 by 120 millimetres 

 ( = specimen figured). 



RANGE OF SPECIES. Barremian to Albian. 



