EXOGYRA. 417 



In the Cenomanian of France and other regions where this species is very 

 abundant it is found to be much more variable than it is in the South of England. 

 This variation is also seen in the specimens found in the Glauconitic Sandstone 

 of Antrim. Variation is particularly noticeable in the size of the left umbo, in the 

 extent of its curvature, the more or less inequilateral character of the shell and in 

 the distinctness of the carina. 1 



In the Cenomanian of Algeria and Tunis, specimens, usually known as Ostrea 

 Mermeti, Coquand, 2 are extremely abundant and very variable ; but Peron, after 

 comparison with numerous French specimens from the same horizon, refers these 

 North African forms without doubt to E. columba. 



Types. — From the Cenomanian of Le Mans. The specimens figured, by Sowerby 

 are in the British Museum ; fig. 1 (upper figure) and fig. 2 are from the Ceno- 

 manian of Le Mans ; fig. 1 (lower figure) is probably from the same locality 

 although labelled " Northampton." 



Distribution. — Upper Greensand (zone of Schloenbacliia rostrata) of Blackdown,. 

 the South Devon and Dorset coasts. Upper Greensand (zone of Pecten asper) of 

 the South Devon and Dorset coasts, Evershot, Askerswell, Eggardon Hill, Little- 

 bredy (Dorset) and Warminster. Chloritic Marl of Compton Bay, Isle of Wight. 

 Cenomanian (Meyer's beds 11, 12) of Beer Head. 



Exogyiia digitata (Soiverby), 1817. Text-figs. 249—252. 



1817. Chama digitata, J. Soiverby. Min. Conch., vol. ii, p. 165, pi. elxxiv, figs. 



1—4. 

 1840. Exogyra laciniata, H. B. Geinitz. Char. d. Schicht. u. Petvef. des siichs. 



Kreidegeb., pt. 2, p. 58. 



1849. Gryph^ea digitata. T.Brown. Ulustr.Foss.Conch. Gt. Brit, and Ireland, 



p. 149, pi. lx, fig. 16. 



1850. Exogyra digitata. H. B. Geinitz. Das Quadersandst. oder Kreidegeb. in 



Deutschland, p. 204. 

 1854. — — J. Morris. Cat. Brit. Foss., ed. 2, p. 166. 



1862. Ostrea Coquandi, Julien, in H. Coquand, Geol. et Pal. Constantine, ph 



xxxiii, figs. 10 — 12. 



1 It should be noted that the apparently small size of the left umbo in the specimens figured by 

 some authors (e. cj. Geinitz) is due to the fact that the specimens are internal casts from which the- 

 thick shell has been removed. 



2 0. Mermeti, Coquand, ' Geol. et Pal. Reg. sud Prov. Constantine' (1862), p. 234, pi. xxiii, figs. 

 3—5 ; Coquand, ' Mon. Ostrea, Terr. Cret,' (1869), p. 131, pi. lii, figs. 10—12 ; Lartet, ' Annal Sci. geol., 

 vol. iii (1873), p. 60, pi. x, figs. 8—16. 0. Larteti, Coquand, op. cit. (1869), p. 153, pi. Ixii, figs. 15, 

 16. 0. Luynesi, Lartet, op. cit. (1873), p. 64, pi. x, figs. 17, 18; Coquand, op. cit. (1869), p. 153, 

 pi. Ixii, figs. 17, 18. 



